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Eradication 

Eradication
Chapter:
Eradication
Author(s):

Andrew Cliff

and Matthew Smallman-Raynor

DOI:
10.1093/med/9780199596614.003.0005
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date: 18 September 2020

  1. 5.1 Introduction [link]

    • Defining Eradication [link]

    • Indicators of Eradicability [link]

    • Spatial Strategies for Eradication [link]

  2. 5.2 Smallpox Eradication [link]

    • The Eradication Campaign [link]

    • Smallpox as a Model for Eradication [link]

  3. 5.3 The Global Polio Eradication Initiative [link]

    • Progress Towards Eradication (1988–2010) [link]

    • Obstacles to Eradication [link]

    • Global Eradication and the Strategic Plan 2010–12 [link]

    • The Long-Term Benefits of Eradication [link]

  4. 5.4 Other Global Eradication Campaigns [link]

    • Campaigns Underway: Dracunculiasis [link]

    • Failed Campaigns [link]

  5. 5.5 Prospects for Future Eradication [link]

    • International Task Force for Disease Eradication (ITFDE) [link]

    • Regional Elimination Campaigns: Measles [link]

  6. 5.6 Hostile Threats: Disease Eradication and Bioterrorism [link]

  7. 5.7 Towards Extinction [link]

    • The Destruction of Known Variola Virus Stocks [link]

  8. 5.8 Conclusion [link]

5.1 Introduction

Future nations will know by history only that the loathsome smallpox has existed and by you has been extirpated.

Thomas Jefferson, A Tribute of Gratitude (letter)

to Edward Jenner (14 May 1806, cited in Stanwell-Smith, 1996, p. 509)

As I look back, I realise that smallpox eradication was achieved, but was just barely achieved. Had the biological and epidemiological characteristics of the disease, or the world political situation, been even slightly more negative, the effort might have failed.

Frank Fenner (1986, [link])

The idea of eradicating a disease has a long and chequered history (Table 5.1). While the vision of a smallpox-free world was articulated in President Thomas Jefferson’s well-known letter of gratitude to Edward Jenner in 1806, the first deliberate effort to eliminate a communicable disease at the national level awaited the early twentieth century and the establishment of the Rockefeller Foundation’s Sanitary Commission for the Eradication of Hookworm Disease in the United States. Several years later, in 1915, the Rockefeller Foundation established the Yellow Fever Commission with the view to eradicating yellow fever globally. This was the first of six campaigns for the global eradication of human pathogens to be launched over the last 100 years (Table 5.2), of which only one (smallpox) has so far achieved the eradication goal (Figure 5.1). Elsewhere, in the animal kingdom, the successful eradication of rinderpest (a viral disease of cattle and other ruminants) was declared by the Food and Agriculture Organization (FAO) in October 2010 (Centers for Disease Control and Prevention, 1993b; Roeder, 2011).

Table 5.1 Milestones in the eradication of human diseases, 1800–2010

Period

Disease

Milestones/events

1800–99

Smallpox

1806: President Thomas Jefferson refers to the ‘extirpation’ of smallpox in his letter to Edward Jenner

Tuberculosis

1888: Charles V. Chapin urges eradication of TB

Rabies

1896: Rabies eliminated from England

1900–49

Yellow fever

1901: Yellow fever eliminated from Havana, Cuba

Hookworm disease

1907: Rockefeller Foundation establishes Sanitary Commission for the Eradication of Hookworm Disease in the USA

Yellow fever

1915: Rockefeller Foundation establishes Yellow Fever Commission to eradicate the disease

Tuberculosis

1917: Decision to eliminate bovine TB from USA

Hookworm disease

1922: Rockefeller Foundation’s hookworm campaign begins to phase out owing to limited success

Yellow fever

1923: Yellow fever reappears in Brazil after an absence of almost one year

Yellow fever

1928–29: Additional outbreaks of yellow fever in Brazil

Yellow fever

1934: Proposal to eliminate Aedes aegypti from Brazil

Tuberculosis

1937: W.H. Frost reports that human tuberculosis is being eliminated from the USA and other countries

Malaria

1941: Anopheles gambiae eliminated from Brazil

Yellow fever

1943: Bolivia is first country to proclaim the elimination of Aedes aegypti

Malaria

1945: Anopheles gambiae eliminated form Egypt

Yellow fever

1947: PAHO adopts proposal for elimination of Aedes aegypti from Americas

1950–99

Smallpox

1950: Pan American Sanitary Conference approves goal of smallpox elimination in the Americas

Yaws

1950: Pan American Sanitary Conference approves goal of yaws elimination in the Americas

Malaria

1951: Malaria eliminated in Sardinia

Yaws

1954: WHO declares goal to eradicate yaws

Malaria

1955: Eighth World Health Assembly adopts goal of global malaria eradication

Smallpox

1958: Eleventh World Health Assembly adopts goal of global smallpox eradication

Smallpox

1966: Nineteenth World Health Assembly adopts goal of intensified smallpox eradication by 1976

Malaria

1969: WHO changes malaria eradication policy to one of malaria control

Smallpox

1970: Smallpox eliminated from the Americas

Malaria

1975: Europe declared free of malaria

Smallpox

1977: Smallpox eradicated worldwide

Measles

1978: USA announces goal to eliminate measles by 1982

Smallpox

1980: WHO declares the global eradication of smallpox

Dracunculiasis

1980: India begins national dracunculiasis elimination programme

Poliomyelitis

1985: PAHO sets goal of poliomyelitis elimination in the Americas by 1990

Measles

1985: Europe sets goal of measles elimination by 2000

Dracunculiasis

1986: Th irty-ninth World Health Assembly declares goal of dracunculiasis elimination

Poliomyelitis

1988: Forty-fi rst World Health Assembly declares goal of global poliomyelitis eradication by 2000

Dracunculiasis

1988: WHO Africa Region sets goal of drancunculiasis elimination from Africa by 1995

Dracunculiasis

1991: Forty-fourth World Health Assembly declares goal of global dracunculiasis eradication by 1995

Poliomyelitis

1991: Last case of indigenous wild virus poliomyelitis in the WHO Americas Region

Onchocerciasis

1991: PAHO resolves to eliminate onchocerciasis morbidity from the WHO Americas Region by 2007

Poliomyelitis

1994: WHO Americas Region certifi ed poliomyelitis-free

Measles

1994: PAHO sets target for measles elimination from the WHO America Region by 2000

Poliomyelitis

1997: Last case of indigenous wild virus poliomyelitis in the WHO Western Pacifi c Region

Measles

1997: WHO Eastern Mediterranean Region sets target for measles elimination by 2010

Poliomyelitis

1998: Last case of indigenous wild virus poliomyelitis in the WHO Europe Region

2000–10

Poliomyelitis

2000: WHO Western Pacifi c Region certifi ed poliomyelitis-free

Poliomyelitis

2002: WHO Europe Region certifi ed poliomyelitis-free

Measles

2002: Indigenous measles virus transmission interrupted in WHO Americas Region

Measles

2003: WHO Western Pacifi c Region sets target for measles elimination by 2012

Measles

2005: WHO Europe Region sets target for measles elimination by 2010

Measles

2008: WHO Africa Region sets a pre-elimination goal for measles

Source: based on Centers for Disease Control and Prevention (1993b, Table 2, [link][link]).

Table 5.2 Eradication initiatives for human disease agents

Disease

Category of agent(s)

Years of eradication effort

Outcome

Yellow fever

Virus

1915–77

Unsuccessful

Yaws

Bacterium

1954–67

Unsuccessful

Malaria

Protozoa

1955–69

Unsuccessful

Smallpox

Virus

1967–79

Successful

Poliomyelitis

Virus

1988–present

Ongoing1

Dracunculiasis

Helminth

1991–present

Ongoing1

Notes: 1 As of January 2012.

Source: based in part on Aylward, et al. (2000, Table 1, p. 1516).

Figure 5.1 The global eradication of smallpox. Statue erected outside the entrance to the main World Health Organization (WHO) building in Geneva, Switzerland. The bronze and stone statue was unveiled on 17 May 2010 by Dr Margaret Chan, Director-General of the WHO, to commemorate the thirtieth anniversary of the WHO’s declaration of the global eradication of smallpox. The statue depicts four persons, one of whom is a girl who is about to be vaccinated by a health worker with a bifurcated needle (inset). The bifurcated needle was designed to hold freeze dried smallpox vaccine between two prongs, with the vaccine administered by a technique (multiple puncture vaccination) that involved up to 15 insertions delivered in rapid succession in a circle of about 5 mm in diameter. The base of the statue shows the continents, while the plaques surrounding the statue (written in the six official languages of the WHO) state that the eradication of smallpox was made possible through the collaboration of nations.

Figure 5.1
The global eradication of smallpox. Statue erected outside the entrance to the main World Health Organization (WHO) building in Geneva, Switzerland. The bronze and stone statue was unveiled on 17 May 2010 by Dr Margaret Chan, Director-General of the WHO, to commemorate the thirtieth anniversary of the WHO’s declaration of the global eradication of smallpox. The statue depicts four persons, one of whom is a girl who is about to be vaccinated by a health worker with a bifurcated needle (inset). The bifurcated needle was designed to hold freeze dried smallpox vaccine between two prongs, with the vaccine administered by a technique (multiple puncture vaccination) that involved up to 15 insertions delivered in rapid succession in a circle of about 5 mm in diameter. The base of the statue shows the continents, while the plaques surrounding the statue (written in the six official languages of the WHO) state that the eradication of smallpox was made possible through the collaboration of nations.

Inevitably, the popularity of eradication as a human disease control strategy has waxed and waned with the successes, setbacks and failures of previous and ongoing campaigns. Many lessons have been learnt from the past (Aylward, et al., 2000) and disease eradication is again at the forefront of global health policy (World Health Organization, 2010b). In the remainder of this introductory section, we define eradication, outline the principal indicators of disease eradicability, and summarise the spatial strategies that may be employed to achieve eradication. In subsequent sections, we chart the successful eradication of smallpox (Section 5.2), the long-running effort to eradicate poliomyelitis (Section 5.3) and the obstacles encountered in other ongoing (dracunculiasis) and failed (yellow fever, yaws and malaria) eradication programmes (Section 5.4). We then look to the prospect of measles eradication (Section 5.5), the issues posed by bioterrorism (Section 5.6) and the outlook for the ultimate extinction of eradicated disease agents (Section 5.7). The chapter is concluded in Section 5.8.

Defining Eradication

As applied to an infectious disease agent, the term eradication has been defined in the literature in a variety of ways and, at times, has been confused with the related term, elimination. To achieve uniformity in the definition and application of terms, the Dahlem Workshop on the Eradication of Infectious Diseases, held in March 1997, defined eradication as the

permanent reduction to zero of the worldwide incidence of infection caused by a specific disease agent as a result of deliberate efforts (Dowdle, 1998, [link]).

Within this definition, the term eradication is reserved for the complete and permanent worldwide cessation of the natural transmission of a disease agent. Eradication thus represents a distinct stage in disease intervention and is distinguished from the related concepts of control, elimination and extinction as defined in Table 5.3.

Table 5.3 Definitions of stages of control of infectious agents and their implications for control programmes

Stages of control

Control

Elimination

Eradication

Extinction

Definition1

“The reduction of disease incidence, prevalence, morbidity and mortality to a locally acceptable level as a result of deliberate efforts.”

Disease: “Reduction to zero of the incidence of a specified disease in a defined geographical area as a result of deliberate efforts”.

Infection: “Reduction to zero of the incidence of infection caused by a specific agent in a defined geographical area as a result of deliberate efforts”.

“Permanent reduction to zero of the worldwide incidence of infection caused by a specific disease agent as a result of deliberate efforts.”

“The specific infectious agent no longer exists in nature or in the laboratory.”

Implication

Continued intervention measures are required to maintain reduction.

Continued intervention measures are required to prevent re-establishment of infection and disease.

Intervention measures no longer needed: all interventions can be halted after certification of eradication.

1 Definitions formulated at the Dahlem Workshop on the Eradication of Infectious Diseases (March 1997), cited in Dowdle (1998, p.23).

Indicators of Eradicability

Following Dowdle (1998) and Aylward, et al. (2000), the potential of a disease agent for eradication can be assessed on the basis of three principal indicators: (1) biological and technical feasibility; (2) costs and benefits; and (3) societal and political considerations. We consider each indicator in turn.

(1) Biological and technical feasibility

The feasibility of eradicating a disease agent is dependent on a range of biological and technical considerations. These include: (i) the availability of an effective means of interrupting the transmission of the disease agent (e.g. a safe and effective vaccine); (ii) the availability of diagnostic tools of sufficient sensitivity and specificity to detect levels of infection that may result in transmission of the disease agent; and (iii) the absence of a non-human vertebrate reservoir and the inability of the disease agent to amplify in the environment.

(2) Costs and benefits

The decision to eradicate a disease agent is contingent on the costs and benefits of the eradication programme, over and above the costs and benefits arising from alternative intervention scenarios. Costs and benefits can be defined in terms of direct effects (i.e. cessation of morbidity and mortality) and consequent effects (i.e. impact on healthcare systems). As eradication programmes are closely related to other health programmes, emphasis should be placed on the costs and benefits to overall health services.

(3) Societal and political considerations

The success or otherwise of eradication programmes is crucially dependent on societal, political and associated financial commitment to their success. The target disease must be recognised as being of public health importance; eradication must be recognised as a worthy goal by society; and political commitment to eradication is required at the highest level throughout the duration of the eradication programme.

Spatial Strategies for Eradication

Viewed in geographical terms, eradication is the last stage in the progressive spatial contraction of a disease and its causative agent. Drawing on the spatial concepts of disease control in Section 1.4, Cliff and Haggett (1989) discuss a stage-by-stage schema of possible contraction strategies, stressing the ways in which geographical considerations impinge upon control by vaccination. These different spatial control strategies are illustrated in Figure 5.2. In the first stage, local elimination, the emphasis is on breaking, in some particular location, the infection chain by vaccination. The theoretical basis of disease elimination through vaccination is discussed in Section 4.3, and is illustrated by the mass vaccination programmes for poliomyelitis and measles elimination in the United States in Section 4.5.

Figure 5.2 Schematic diagram of four spatial and aspatial control strategies to prevent epidemic spread. Infected areas are shaded; disease-free areas are unshaded. The strategies of defensive isolation (B) and offensive containment (C) have already been encountered in Figure 1.20 and are reproduced here as part of the broader suite of spatial control strategies.

Figure 5.2
Schematic diagram of four spatial and aspatial control strategies to prevent epidemic spread. Infected areas are shaded; disease-free areas are unshaded. The strategies of defensive isolation (B) and offensive containment (C) have already been encountered in Figure 1.20 and are reproduced here as part of the broader suite of spatial control strategies.

Source: redrawn from Cliff and Haggett (1989, Figure 2, p. 318).

Once an area is free from the indigenous transmission of a disease agent, then there is need for the establishment of spatial barriers to disease transmission in the form of defensive isolation and offensive containment. These barrier concepts are described in Section 1.4but, in essence, both seek to limit the spatial spread of a disease agent into disease-free areas.

The final stage of global eradication would arise in principle from a combination of the previous three methods: infected areas would be progressively reduced in size, and the coalescence of such disease-free areas would lead, eventually, to the elimination of the disease on a worldwide basis. For vaccine-preventable diseases, eradication therefore rests on a globally coordinated vaccination programme to reduce the sizes of geographically distributed at-risk populations to levels at which the chains of infection cannot be maintained. In terms of the Bartlett model (Section 1.4), this means systematically reducing the wave order of different communities from I to II, and from II to III, eventually bringing the Type III waves into phase so that disease fade-out in all the remaining disease-active areas coincides.

5.2 Smallpox Eradication

At the time of writing, smallpox is the only human disease to have been eradicated globally. As described by Fenner, et al. (1988), the practical reality of devising, coordinating and financing a field programme involving more than 30 national governments, as well as some of the world’s most complex cultures and demanding environments, proved to be of heroic proportions. Until the mid-1960s, control of smallpox was based primarily upon mass vaccination to break the chain of transmission between infected and susceptible individuals by eliminating susceptible hosts. Although this approach had driven the disease from the developed world, the less developed world remained a reservoir area. Thus between 1962 and 1966, some 500 million people in India were vaccinated, but the disease continued to spread. Between 5–10 percent of the population always escaped the vaccination drives, concentrated especially in the vulnerable under-15 age group. Nevertheless, the susceptibility of the virus to concerted action had been demonstrated and led to critical decisions at the Nineteenth World Health Assembly in 1966.

The Eradication Campaign

The Nineteenth World Health Assembly committed the World Health Organization (WHO) to a 10-year global smallpox eradication programme which was launched in 1967. As we noted in Section 2.7, the eradication campaign started with mass vaccination, but the importance of surveillance and selective control was soon recognised. Contacts of smallpox cases were traced and vaccinated, as well as the other individuals in those locations where the cases occurred. The success of these strategies may be judged from Figure 5.3. By 1970, retreat was under way in parts of Africa. By 1973, smallpox had been eliminated in the Americas while, by 1976, the disease had been pushed out of Southeast Asia and only a part of East Africa remained to be cleared. The world’s last naturally occurring case of smallpox was finally tracked down to the Somalian town of Merka in late October 1977 (Figure 5.4). After a two-year period during which no further cases (other than laboratory accidents) were recorded, WHO formally announced at the end of 1979 that the global eradication of smallpox was complete (Figure 5.5).

Figure 5.3 Global eradication of smallpox under the WHO Intensified Programme, 1967–77. Countries with smallpox cases for the year in question are marked in black.

Figure 5.3
Global eradication of smallpox under the WHO Intensified Programme, 1967–77. Countries with smallpox cases for the year in question are marked in black.

Source: Cliff, et al. (1998, Figure 7.25, pp. 374–[link]), redrawn from Fenner, et al. (1988, Figure 10.4 and Plates 10.42–10.51, pp. 516–[link] passim).

Figure 5.4 The last ‘natural’ case of smallpox. Ali Maow Maalin, the last case of naturally occurring smallpox in the world, developed a rash on 26 October 1977, in the town of Merka, Somalia.

Figure 5.4
The last ‘natural’ case of smallpox. Ali Maow Maalin, the last case of naturally occurring smallpox in the world, developed a rash on 26 October 1977, in the town of Merka, Somalia.

Source: Fenner, et al. (1988, Plate 22.10, p. 1066).

Figure 5.5 Global smallpox eradication document. The official parchment certifying the global eradication of smallpox, dated 9 December 1979. This is arguably the most important document in the history of twentieth-century medicine.

Figure 5.5
Global smallpox eradication document. The official parchment certifying the global eradication of smallpox, dated 9 December 1979. This is arguably the most important document in the history of twentieth-century medicine.

Source: Fenner, et al. (1988, Frontispiece).

Smallpox as a Model for Eradication

It is important to consider how far smallpox is a useful control model for the eradication of other communicable diseases. For whatever the huge difficulties in practice, in principle, smallpox was well suited to global eradication. Fenner (1986) has summarised the biological and socio-political characteristics of smallpox that facilitated global eradication (Table 5.4). First and foremost among the biological features, smallpox was such a severe disease that it was clearly worth the effort required for eradication. Second, variola virus was a specific human virus; there is no animal reservoir. Third, sub-clinical infections were virtually unknown, and those that did occur excreted very little virus and were of no epidemiological importance. Fourth, spread usually resulted from direct face-to-face contact with patients with a rash; patients were not infectious during the incubation period or the pre-eruptive phase. If cases were isolated as soon as the rash was apparent, in a setting in which they had contact only with vaccinated or immune persons, the chain of transmission could be broken. Fifth, neither a prolonged carrier state nor recurrence of clinical illness with associated infectivity ever occurred in smallpox; hence the disappearance of acute infections meant that the chance of transmission had been eliminated. Sixth, there was only one serotype of variola virus – over centuries of time and all over the world – and, seventh, since the time of Jenner, there has been an effective live-virus vaccine against smallpox. Additionally, in the 1950s, a freeze-dried vaccine was developed that was stable even under the most adverse conditions (Fenner, 1986).

Table 5.4 Biological and socio-political features which favoured the global eradication of smallpox

Biological features

1. A severe disease, with high mortality and serious after-effects

2. No animal reservoir of variola virus

3. Very few sub-clinical cases

4. Cases became infectious at time of onset of rash

5. Recurrence of infectivity never occurred

6. Only one serotype existed

7. An effective, stable vaccine was available

Socio-political features

8. Earlier country-wide elimination showed that global eradication was an attainable goal

9. There were few social or religious barriers to the recognition of cases

10. The costs of quarantine and vaccination for travellers provided a strong financial incentive for wealthy countries to contribute

11. The Intensified Smallpox Eradication Unit of the WHO had inspiring leaders and enlisted devoted health workers

Source: Cliff, et al. (1993, Table 16.2, p. 422), originally from Fenner (1986, Table 1, [link]).

In addition to the biological features of smallpox, several socio-political factors were also crucial to the success of the eradication campaign. Point 10 in Table 5.4 argues that smallpox imposed a heavy financial burden on the industrialised countries, as well as on those where smallpox was endemic. Quite apart from the disease and death from smallpox itself, the cost of vaccination, plus that of maintaining quarantine barriers, is calculated to have been about US$1,000 million per annum in the last years of the virus’s existence in the wild (Fenner, 1986).

5.3 The Global Polio Eradication Initiative

Although significant differences in the characteristics of smallpox and poliomyelitis render the eradication of poliomyelitis a potentially more difficult task than was the case for smallpox (Table 5.5), the feasibility of global poliomyelitis eradication on biological grounds is established in principle (Table 5.6). On this basis, the Forty-first World Health Assembly (May 1988) adopted the historic Resolution WHA41.28 that committed the WHO to the global eradication of poliomyelitis by the year 2000 (article 1). The eradication effort was to be pursued in a manner which strengthened the development of the Expanded Programme on Immunization (EPI) and the health infrastructure of member states more generally (article 2). Member states in which at least 70 percent of target populations had already received poliovirus vaccine were invited to formulate plans for the elimination of indigenous wild poliovirus (article 3), while member states with vaccine coverage of less than 70 percent were encouraged to surpass that level as soon as possible (article 4). Member states in which absence of the disease had already been confirmed were requested to sustain their efforts and to share their technical expertise and resources (article 5), while all member states were urged to intensify surveillance for poliomyelitis and to provide rehabilitation services for as many children as possible who were crippled by the disease (article 6) (World Health Organization, 1988).

Table 5.5 Biological and socio-political characteristics that favoured the global eradication of smallpox: comparisons with poliomyelitis and measles

Features

Smallpox

Poliomyelitis

Measles

Biological

1. Reservoir host in wildlife

No

No

No

2. Persistent infection occurs

No

No

No

3. Number of serotypes

1

3

1

4. Antigenic stability

Yes

Yes

Yes

5. Vaccine effective

Yes

Yes

Yes

Cold chain necessary

No

Yes

No

Number of doses

1

4

1

6. Infectivity during prodromal

No

Yes

Yes

7. Sub-clinical cases occur

No

Yes

No

8. Early containment of outbreak possible

Yes

No

No

Socio-political

9. Country-wide elimination achieved

Yes

Yes

Yes

10. Incentive for industrialised countries to assist

Strong

Weak

Weak

11. Records of vaccination required

No

Yes

Yes

12. Improved sanitation required

No

Yes

No

Source: Cliff, et al. (1993, Table 16.3, p. 423), originally from Fenner (1986, Table 2, [link]).

Table 5.6 Biological principles for the global eradication of poliomyelitis

Biological principle

Notes

Poliovirus causes acute, non-persistent infection

The lack of a long-term or persistent carrier state is a key characteristic of poliomyelitis which underpins the feasibility of global eradication. In rare instances, however, persons with primary immunodeficiency disorders have been shown to excrete vaccine virus for six months or more. The long-term excretors have significant implications for when and how OPV use should cease in the wake of the certification of poliomyelitis eradication.

Poliovirus is transmitted only by infectious humans or their waste

Poliovirus is transmitted by droplet spread from the pharynx or by the faecal contamination of hands, eating utensils, food or water. Epidemiological evidence suggests that at least 80 percent of infections with poliovirus are person-to-person (faecal–oral or oral–oral) and that vectors play only a very limited, if any, role in epidemic propagation.

Survival of poliovirus in the environment is finite

While poliovirus may contaminate soil, sewage and surface water, the presence of virus in the environment is the direct result of the recent presence of virus in the human population. Environmental survival is finite; even under favourable conditions, the virus is inactivated in months.

Humans are the only reservoir of poliovirus

Although poliovirus has been identified in shellfish, the virus does not replicate in these organisms and only remains as long as the surrounding waters are polluted. No evidence of infection with poliovirus has been found in domestic and peridomestic animals, while non-human primates are unlikely reservoirs in nature.

Vaccination interrupts poliovirus transmission

Oral poliovirus vaccine (OPV) produces both intestinal and serological immunity to poliovirus, thereby serving to halt the transmission of wild virus in highly vaccinated populations.

Source: based on Dowdle and Birmingham (1997).

Progress Towards Eradication (1988–2010)

The Global Polio Eradication Initiative is founded upon approaches and processes that were developed by the Pan American Health Organization (PAHO) for the elimination of poliomyelitis in the Americas. As summarised in Table 5.7, there are four main strands to the global programme: high routine immunisation coverage; national immunisation days (NIDs); acute flaccid paralysis surveillance; and intensive ‘mopping-up’ immunisation campaigns. Oral poliovirus vaccine (OPV) is the vaccine of choice for both routine and mass immunisation.

Table 5.7 Strategies for the global eradication of poliomyelitis

Eradication strategy

Notes

High routine infant immunisation coverage with OPV

The aim is to immunise, through routine vaccination services, ≥ 90 percent of infants with four doses of OPV by one year of age. In order to prevent the re-establishment of wild poliovirus through importation, high levels of routine immunisation should also be maintained in poliomyelitis-free regions.

National immunisation days (NIDs)

Supplementary immunisation activities in the form of NIDs provide an effective vehicle for the rapid and massive dissemination of vaccine strains of poliovirus. The aim of NIDs is to interrupt the circulation of wild poliovirus by immunising all members of the target group (generally children aged < 5 years), regardless of prior immunisation status. National immunisation days are conducted in two rounds, separated by 4–6 weeks, with each round being completed as quickly as possible (usually 1–3 days) and with logistic and biological considerations favouring the delivery of rounds in the cool/dry season. Annual NIDs, conducted over 3–5 consecutive years, are generally required to eradicate wild poliovirus in areas where routine immunisation is low. ‘Synchronised’ NIDs, with immunisation days coordinated between countries, provide an effective platform for international interventions.

Acute flaccid paralysis (AFP) surveillance

The syndromic surveillance strategy, requiring the immediate reporting and rapid laboratory-based investigation of all cases of AFP in children aged < 15 years serves in the detection of typical and atypical cases of poliomyelitis due to both wild and vaccine-derived strains of poliovirus. In addition, AFP surveillance provides a basis for assessment of the quality of disease surveillance for certification purposes. Molecular epidemiologic methods have enhanced the precision and reliability of laboratory-based poliomyelitis surveillance, allowing wild viruses to be classified into genetic families from which inferences on the geographical source of isolates can be drawn.

‘Mopping-up’ immunisation campaigns

‘Mopping-up’ immunisation campaigns are used to interrupt the final chains of poliovirus transmission in the last remaining reservoirs, or suspected reservoirs, of wild poliovirus. These localised campaigns involve the delivery of two doses of OPV to all children aged < 5 years in the target area, with the doses separated by one month. To ensure maximum coverage of the target population, vaccine administration is undertaken on a house-to-house basis.

Source: based on Hull, et al. (1997).

The Global Picture

Although the original WHO target date for poliomyelitis eradication (2000) was missed, and there have been further disappointments along the way, substantial progress towards the ultimate goal of poliomyelitis eradication has been made over the years. As Figure 5.6 shows, the global count of reported poliomyelitis cases tumbled with the continued rise in vaccination coverage, from 34,597 cases (1988) to 1,413 cases (2010). The associated sequence of poliomyelitis retreat over these years is mapped by country according to a three-category classification of disease status (endemic, non-endemic and certified poliomyelitis-free) in Figure 5.7. During the course of the 23-year observation interval, the number of poliomyelitis-endemic countries was whittled down from 125 (1988) to four (2010). Wild poliovirus transmission was interrupted in the Americas in 1991 (Figure 5.8), the Western Pacific in 1997 and Europe in 1998, with certification of the poliomyelitis-free status of these regions in 1994, 2000 and 2002 respectively (see Figure 4.4). Elsewhere, the scaling up of eradication activities from the mid-to-late 1990s resulted in a marked contraction of the disease in Africa, the Eastern Mediterranean and South-East Asia so that, by 2010, endemic activity had been pushed back to a handful of strongholds in West Africa (Nigeria) and South Asia (Afghanistan, India and Pakistan) (Figure 5.7). By this time, the global transmission of wild poliovirus type 2 had been interrupted, and all reported cases of wild virus infection were associated with poliovirus types 1 and 3.

Figure 5.6 Global series of poliomyelitis cases, 1974–2010. The bar chart plots the annual count of poliomyelitis cases as reported to the World Health Organization (WHO). Black bars identify the period covered by the Global Polio Eradication Initiative (1988–2010). Line traces plot WHO/UNICEF estimates of the global coverage of infants with a third dose of poliovirus vaccine (Pol3).

Figure 5.6
Global series of poliomyelitis cases, 1974–2010. The bar chart plots the annual count of poliomyelitis cases as reported to the World Health Organization (WHO). Black bars identify the period covered by the Global Polio Eradication Initiative (1988–2010). Line traces plot WHO/UNICEF estimates of the global coverage of infants with a third dose of poliovirus vaccine (Pol3).

Source: data from the World Health Organization (www.who.int).

Figure 5.7 Progress towards the global eradication of poliomyelitis, 1988–2010. Countries are classified as endemic (black shading), non-endemic (grey shading) and certified poliomyelitis-free (unshaded). In recognition of the persistent spread (> 12 months) of imported wild polioviruses in some formerly non-endemic countries of the WHO Africa and Eastern Mediterranean Regions, the additional category of re-established transmission is indicated on the map for 2010. Note that re-established transmission was suspected (but not confirmed) for Sudan. The bar chart shows the number of countries that reported cases of poliomyelitis to WHO each year.

Figure 5.7
Progress towards the global eradication of poliomyelitis, 1988–2010. Countries are classified as endemic (black shading), non-endemic (grey shading) and certified poliomyelitis-free (unshaded). In recognition of the persistent spread (> 12 months) of imported wild polioviruses in some formerly non-endemic countries of the WHO Africa and Eastern Mediterranean Regions, the additional category of re-established transmission is indicated on the map for 2010. Note that re-established transmission was suspected (but not confirmed) for Sudan. The bar chart shows the number of countries that reported cases of poliomyelitis to WHO each year.

Source: data from the World Health Organization (www.who.int).

Figure 5.8 The elimination of poliomyelitis in the Americas. This evocative photograph, taken in 1995, shows Luis Fermín Tenorio of Junín, Peru, the last recorded case of wild virus poliomyelitis in the WHO Region of the Americas.

Figure 5.8
The elimination of poliomyelitis in the Americas. This evocative photograph, taken in 1995, shows Luis Fermín Tenorio of Junín, Peru, the last recorded case of wild virus poliomyelitis in the WHO Region of the Americas.

Source: WHO/PAHO (photograph by A. Waak).

Obstacles to Eradication

International Importations and Re-Established Transmission

Throughout the eradication campaign, poliomyelitis-free countries have been under threat from the importation of poliovirus from the remaining endemic regions. The threat has been especially pronounced in those poliomyelitis-free developing countries that, following the cessation of supplementary immunisation activities, have experienced a declining level of immunity to the disease. Sample importations of wild poliovirus into poliomyelitis-free countries are illustrated for the period 1999–2003 in Figure 5.9. While the map highlights the particular role of India as the source of wild poliovirus in a number of European, Middle Eastern and East Asian states, the resurgence of poliovirus activity in connection with the West African state of Nigeria has proved particularly problematic in recent years. As described in Section 4.6, the temporary suspension of immunisation activities in several states of Nigeria in 2003–4 contributed to the spread of wild polioviruses to other countries of the WHO Africa Region and beyond. By 2010, re-established poliovirus transmission (defined as > 12 months of persistent transmission of imported wild polioviruses) was observed in Angola, Chad, Democratic Republic of Congo and, possibly, Sudan (Figure 5.7). To these countries can be added others that recorded outbreaks associated with imported polioviruses in 2010 and 2011, including countries of the WHO Western Pacific (China) and Europe (Kazakhstan, Russian Federation, Tajikistan and Turkmenistan) Regions that had been certified free of wild virus poliomyelitis in earlier years (Table 5.8).

Figure 5.9 Sample importations of wild poliovirus into poliomyelitis-free areas, 1999–2003. Countries in which wild poliovirus was endemic at the end of the observation period are identified by the diagonal shading category. Countries in which importations of wild poliovirus were recorded are identified by the grey shading category.

Figure 5.9
Sample importations of wild poliovirus into poliomyelitis-free areas, 1999–2003. Countries in which wild poliovirus was endemic at the end of the observation period are identified by the diagonal shading category. Countries in which importations of wild poliovirus were recorded are identified by the grey shading category.

Source: redrawn from Smallman-Raynor, et al. (2006, Figure 12.17, p. 607), originally from World Health Organization (2003, Figure 9, [link]).

Table 5.8 Wild poliovirus cases reported to WHO in 2010 and 2011

Country

2010

20111

Endemic

Afghanistan

25

59

India

42

1

Nigeria

21

45

Pakistan

144

167

Re-established transmission

Angola

33

5

Chad

26

125

DR Congo

100

87

Outbreak countries

Central African Republic

0

2

China

0

18

Guinea

0

3

Kenya

0

1

Côte d’Ivoire

0

36

Niger

2

2

Mali

4

7

Congo

441

1

Gabon

0

1

Uganda

4

0

Russian Federation

14

0

Liberia

2

0

Nepal

6

0

Kazakhstan

1

0

Tajikistan

460

0

Turkmenistan

3

0

Senegal

18

0

Mauritania

5

0

Sierra Leone

1

0

Total

1,352

560

Notes: data reported to WHO as of 5 December 2011.

Source: Global Polio Eradication Initiative (www.polioeradication.org).

Conflict and Security

Wars, particularly in Central America, South Asia and sub-Saharan Africa, have consistently posed one of the single greatest obstacles to the effective implementation of the Global Poliomyelitis Eradication Initiative. In some countries, the war-related disruption of immunisation services has triggered major outbreaks of poliomyelitis and other vaccine-preventable diseases. In the Russian Federation, for example, an outbreak of poliomyelitis in Chechnya during the mid-1990s was consequent upon three years of severe disruption to the health services. Likewise, in Iraq, an outbreak of poliomyelitis in 1999 was associated with continuing unrest in the north of the country (Bush, 2000; Tangermann, et al., 2000). Among those countries in which wild polioviruses continued to be endemic in 2010–11, limited access to conflict-affected areas of Afghanistan (South Region) and Pakistan (Afghan border area) poses a substantial and ongoing threat to the success of the Global Polio Eradication Initiative (Centers for Disease Control and Prevention, 2011d).

Ceasefires and ‘periods of tranquillity’ have occasionally been negotiated between hostile factions to allow the implementation of disease control and eradication initiatives in conflict-affected areas. Indeed, such health-inspired breaks in fighting have been viewed not only as a means of permitting the delivery of disease intervention measures but also as an informal channel of communication and peace brokering (Bush, 2000). Examples of states in which ceasefires, periods of tranquillity and various unofficial truces have been negotiated for the purposes of poliomyelitis immunisation include Afghanistan, Angola, Cambodia, El Salvador, Iraq, Myanmar, Sri Lanka and Sudan (World Health Organization, 1997; Tangermann, et al., 2000; Centers for Disease Control and Prevention, 2011d).

Circulating Vaccine-Derived Polioviruses (cVDPVs)

One long-standing public health concern over the use of OPV – the potential for attenuated Sabin strains of poliovirus to revert to the neurovirulence of wild poliovirus and to persist, circulate and cause poliomyelitis outbreaks – was thrown into sharp focus at the turn of the millennium. Between July 2000 and September 2001, 21 cases of paralytic poliomyelitis were identified in the Caribbean island of Hispaniola. The causative agent of the outbreak, which affected both the Dominican Republic (13 cases) and Haiti (8 cases), was found to be a type 1 circulating vaccine-derived poliovirus (cVDPV) – a variant of an attenuated (Sabin) type 1 strain that demonstrated evidence of prolonged replication. With heightened global surveillance for vaccine-derived polioviruses, further outbreaks of cVDPVs have been documented in, among other countries, Afghanistan, Ethiopia, India, Madagascar and the Philippines (Kew, et al., 2004; Centers for Disease Control and Prevention, 2011b).

Global Eradication and the Strategic Plan 2010–12

To capitalise on the achievements of the previous 20 years, the Global Polio Eradication Initiative’s (2010) Global Polio Eradication Strategic Plan 2010–12 lays out the milestones to the end of 2012 for the global interruption of wild poliovirus transmission. These milestones include: (1) the interruption of wild poliovirus transmission following importation in countries with outbreaks in 2009 by mid-2010; (2) the interruption of wild poliovirus transmission in countries with re-established transmission (Angola, Chad, Democratic Republic of the Congo and, possibly, Sudan) by the end of 2010; (3) the interruption of wild poliovirus transmission in at least two of the remaining four endemic countries (Afghanistan, India, Nigeria and Pakistan) by the end of 2011; and (4) the interruption of wild poliovirus transmission in all countries by the end of 2012. An interim assessment of progress towards these milestones, provided by the Global Polio Eradication Initiative’s Independent Monitoring Board in March–April 2011, concluded that Milestone (1) was ‘on track’, Milestone (2) had been ‘missed’, while Milestones (3) and (4) were ‘at risk’ (World Health Organization, 2011b). At a subsequent meeting, in September 2011, the Board concluded from the evidence that

The GPEI [Global Polio Eradication Initiative] is not on track to interrupt polio transmission by the end of 2012, as had been planned. Indeed…there is substantial risk that stopping transmission will take much longer than the period that remains between now and the end of 2012 (World Health Organization, 2011d, pp. 557–[link]).

Looking Forwards: Post-Wild Virus Eradication

Assuming that the global interruption of wild poliovirus transmission will be achieved at some future date (Figure 5.10), the Strategic Plan 2010–12 outlines the activities that will be required to certify the achievement and to minimise risks that may arise from two main sources:

  1. (1) vaccine-derived polioviruses, resulting in (i) vaccine-associated paralytic poliomyelitis (VAPP) either in single cases or outbreaks, (ii) outbreaks due to circulating vaccine-derived polioviruses (cVDPVs) and (iii) long-term excretion of VDPVs by individuals with primary immunodeficiency disorders (iVDPVs);

  2. (2) wild polioviruses, resulting from (i) unintentional release from a contained facility (laboratory or vaccine manufacturing site) or (ii) intentional release due to an act of bioterrorism or biological warfare.

Figure 5.10 Rotary International and the Global Polio Eradication Initiative. Rotary International is one of the four spearheading partners of the Global Polio Eradication Initiative, the others being WHO, US Centers for Disease Control and Prevention and UNICEF. Rotary International established the PolioPlus programme in 1985 and, since that time, the organisation has contributed over US$700 million to the eradication initiative. The poster looks forward to a world without polio.

Figure 5.10
Rotary International and the Global Polio Eradication Initiative. Rotary International is one of the four spearheading partners of the Global Polio Eradication Initiative, the others being WHO, US Centers for Disease Control and Prevention and UNICEF. Rotary International established the PolioPlus programme in 1985 and, since that time, the organisation has contributed over US$700 million to the eradication initiative. The poster looks forward to a world without polio.

Source: Rotary International (www.rotary.org).

Risk minimisation in the post-wild virus transmission era is planned to involve the three stages depicted in Figure 5.11, namely:

Figure 5.11 Timeline of activities for minimising long-term poliovirus risks following the global interruption of wild poliovirus transmission. AFP = acute flaccid paralysis; OPV = oral poliovirus vaccine; (c) VAPP = (circulating) vaccine-associated paralytic poliomyelitis; VDPV = vaccine-derived poliovirus; WPV = wild poliovirus.

Figure 5.11
Timeline of activities for minimising long-term poliovirus risks following the global interruption of wild poliovirus transmission. AFP = acute flaccid paralysis; OPV = oral poliovirus vaccine; (c) VAPP = (circulating) vaccine-associated paralytic poliomyelitis; VDPV = vaccine-derived poliovirus; WPV = wild poliovirus.

Source: redrawn from Global Polio Eradication Initiative (2010, [link]).

Stage 1: Wild Poliovirus Containment and Certification. This stage involves the destruction or safe storage of infectious or potentially infectious materials, along with the certification of the interruption of global transmission and the containment of wild poliovirus stocks.

Stage 2: VAPP/VDPV Elimination Phase. This stage will begin the eventual cessation of the routine use of trivalent OPV in order to eliminate VAPP and the risks of virus re-emergence associated with cVDPVs. AFP surveillance and poliovirus outbreak response capacity will have to be maintained during this phase.

Stage 3: Post-OPV Era. This stage is the final stage of the Global Polio Eradication Initiative and will begin with the verification that VDPVs are no longer in circulation.

Ultimately, the Strategic Plan 2010–12 envisages the transition of existing human resources, physical infrastructure and institutional arrangements away from the Global Polio Eradication Initiative to other priority areas in disease surveillance and control. While the preparatory work for this ‘mainstreaming’ process can be traced to the 1990s, efforts have been accelerated since 2004 and will continue into the eradication era.

The Long-Term Benefits of Eradication

Economic Benefits

Given the massive investment of time and resources in the Global Polio Eradication Initiative, a fundamental question arises as to the long-term financial benefits that will accrue once the disease has been finally extinguished (cf. Section 6.5). Based on the projected eradication of poliomyelitis by 2005, a cost–benefit analysis by Bart, et al. (1996) placed the ‘break-even’ point – the point at which the financial benefits of eradication exceed the costs – in 2007, with a cumulative global saving of US$13.6 billion by 2040. In a more recent analysis, undertaken for the interval 1970–2050 and with an assumed cessation of poliovirus vaccination after eradication in 2010, Khan and Ehreth (2003) estimate the cumulative global costs of vaccination at US$73 billion and the associated savings in medical care costs at US$129 billion – a net saving of over US$55 billion. Incremental net benefits of a similar order of magnitude (US$40–50 billion) for the period 1988–2035, based on the assumed interruption of wild poliovirus transmission in 2012, have been projected by Duintjer Tebbens, et al. (2011).

Human Benefits

Apart from the direct economic benefits of the Global Polio Eradication Initiative, the final elimination of poliomyelitis will relieve the world of a major cause of human suffering and death. Some impression of the magnitude of the long-term human benefits can be gained from Table 5.9. Again assuming an eradication date of 2010, the table suggests that poliomyelitis control and eradication efforts will avert some 42 million poliomyelitis cases and 855,000 poliomyelitis deaths in the eight decades to 2050. Recognising the crippling nature of poliomyelitis, the avoided morbidity and mortality translates into a long-term saving of 39.6 million disability-adjusted life years (DALYs) (Khan and Ehreth, 2003).

Table 5.9 Estimated number of poliomyelitis cases and deaths averted, and disability-adjusted life years (DALYs) saved, by routine poliomyelitis immunisation and eradication, 1970–2050

WHO region

Poliomyelitis cases averted (millions)

Poliomyelitis deaths averted (thousands)

DALYs saved (thousands)

Africa

6.89

131

4,426

Americas

9.33

193

10,262

Eastern Mediterranean

4.33

90

3,896

Europe

4.21

88

7,066

South-East Asia

9.05

188

6,762

Western Pacific

7.92

165

7,201

World

41.73

855

39,613

Source: information from Khan and Ehreth (2003, Table 2, p. 704).

5.4 Other Global Eradication Campaigns

This section examines the several other eradication initiatives that, at various times over the last century, have been launched against human infectious diseases (Table 5.2). We begin with the ongoing campaign to eradicate one of the WHO’s ‘neglected tropical diseases’, dracunculiasis. We then consider the failed efforts to eradicate yellow fever, yaws and malaria.

Campaigns Underway: Dracunculiasis

Dracunculiasis (Guinea worm disease) is a tropical infection of subcutaneous and deeper tissues by the large nematode Dracunculus medinensis. Humans are the only known reservoir of D. medinensis, with transmission occurring through the ingestion of water from infested wells and ponds. Improving standards of water supply in the first half of the twentieth century reduced the distribution of dracunculiasis. Deliberate campaigns eliminated it from the southern area of the Soviet Union in the 1930s and from Iran in the 1970s. The United Nations-sponsored International Drinking Water Supply and Sanitation Decade of the 1980s called further attention to the disease, and a number of endemic countries (for example, India) began national elimination campaigns. Framed by these developments, the Thirty-ninth World Health Assembly (1986) adopted a resolution calling for the elimination of the disease on a country-by-country basis. This resolution was reinforced when the Forty-fourth World Health Assembly (1991) committed the WHO to the global eradication of dracunculiasis by 1995.

Eradication Feasibility and Strategies

As described by Hopkins and Ruiz-Tiben (1991), a series of biological and socio-political factors make the eradication of dracunculiasis feasible. These include: (1) the easy and unambiguous recognition of the condition; (2) the restriction of the intermediate host (copepods) to water bodies; (3) the availability of simple and cost-effective interventions; (4) the limited geographical distribution and seasonal nature of disease transmission; (5) the absence of an animal reservoir for D. medinensis; and (6) the availability of political commitment to the eradication initiative. The principal strategies for eradication are based around the education of at-risk populations, close surveillance and case containment in known endemic villages and the implementation or specific interventions to ensure access to safe water, including the use of filters and the control of copepod populations through the use of temephos insecticide (Figure 5.12).

Figure 5.12 Dracunculiasis (Guinea worm disease). A hoarding to promote public awareness of the dracunculiasis eradication campaign in the WHO Africa Region. Note the request for information on actual and suspected cases of the disease, with a view to enhancing surveillance and case containment activities.

Figure 5.12
Dracunculiasis (Guinea worm disease). A hoarding to promote public awareness of the dracunculiasis eradication campaign in the WHO Africa Region. Note the request for information on actual and suspected cases of the disease, with a view to enhancing surveillance and case containment activities.

Source: World Health Organization (www.who.int).

Progress of the Eradication Campaign

Progress towards the global eradication of dracunculiasis is summarised for the period 1991–2010 in Figures 5.13 and 5.14. At onset of the eradication initiative in 1991, almost 548,000 cases of the disease were reported from a band of 20 endemic countries that extended from West Africa to the Indian subcontinent (Figure 5.13A). Although the number of reported cases fell rapidly in subsequent years (Figure 5.14), the original eradication target date (1995) was missed and the disease still remained endemic in 13 countries of sub-Saharan Africa at the turn of the millennium (Figure 5.13B). Commitment to the eradication campaign was maintained throughout the first decade of the twenty-first century such that, by 2010, 180 countries worldwide had been certified free of the disease; indigenous transmission was limited to just five African states (Chad, Ethiopia, Ghana, Mali and Sudan; see Figure 5.13D), with Sudan accounting for the majority of reported cases (Figure 5.14). As of mid-2011, endemic activity had been pushed back to Ethiopia, Mali and the newly-created South Sudan, with insecurity (sporadic violence and civil unrest) in the latter two countries being viewed as the greatest threat to the success of the campaign (Hopkins, et al., 2011).

Figure 5.13 Progress towards the global eradication of dracunculiasis, 1991–2010. The situation is shown for the period immediately preceding the onset of the eradication campaign (A) and at the start of 2000 (B), 2005 (C) and 2010 (D). Shading categories identify countries as endemic (black) or certified dracunculiasis-free (grey); other countries (unshaded) were at the precertification stage or were not known to have dracunculiasis but had yet to be certified.

Figure 5.13
Progress towards the global eradication of dracunculiasis, 1991–2010. The situation is shown for the period immediately preceding the onset of the eradication campaign (A) and at the start of 2000 (B), 2005 (C) and 2010 (D). Shading categories identify countries as endemic (black) or certified dracunculiasis-free (grey); other countries (unshaded) were at the precertification stage or were not known to have dracunculiasis but had yet to be certified.

Source: World Health Organization (www.who.int).

Figure 5.14 Dracunculiasis, 1991–2010. (Bar chart) Annual count of reported cases of dracunculiasis worldwide. (Inset) Annual count of reported cases of dracunculiasis, Sudan and the rest of the world, 1996–2010.

Figure 5.14
Dracunculiasis, 1991–2010. (Bar chart) Annual count of reported cases of dracunculiasis worldwide. (Inset) Annual count of reported cases of dracunculiasis, Sudan and the rest of the world, 1996–2010.

Source: data from the World Health Organization (www.who.int).

Failed Campaigns

Of the eradication initiatives in Table 5.2 that have so far been concluded, three (yellow fever, yaws and malaria) ended in failure. The critical factors that contributed to these unsuccessful outcomes are summarised in Table 5.10 and include: (i) lack of biological and technical feasibility (yellow fever, yaws and malaria); (ii) lack of detailed economic analyses to justify or support the eradication effort (yellow fever and yaws); and (iii) lack of broad-based societal and political support (yellow fever, yaws and malaria) (Aylward, et al., 2000). In the remainder of this section, we review the failed Global Malaria Eradication Programme of 1955–69. Our account draws on Cliff, Smallman-Raynor, Haggett, et al. (2009, pp. 243–[link]).

Table 5.10 Factors contributing to the failure of disease eradication campaigns

Factor

Yellow fever (1915–77)

Yaws (1954–67)

Malaria (1955–69)

Biological and technical feasibility

Not feasible: animal (non-human primate) reservoir of yellow fever virus.

Not feasible: prevalence and importance of inapparent latent infections was underestimated.

Not feasible: widespread development of vector resistance to insecticides.

Costs and benefits

Economic analyses to justify the campaign were not undertaken until the 1970s.

Economic analyses to justify the campaign were lacking in specific detail.

1

Societal and political considerations

Broad-based political support for eradication was difficult to secure.

Broad-based political support for eradication was difficult to secure.

Political support was secured through the World Health Assembly, although many Member States were not fully aware of their commitments.

Notes: 1 Economic analyses played an important role in justifying the malaria eradication campaign.

Source: based on information in Aylward, et al. (2000, pp. 1515–16).

The Global Malaria Eradication Programme (1955–69)

The development of the insecticide DDT (dichloro–diphenyl–trichloroethane) revolutionised the post-war control of malaria mosquitoes. With the combined virtues of low cost, ready availability and high and long-lasting potency for insects, early reports of the residual application of DDT in parts of southern Europe and the Americas demonstrated the potential for the insecticide to interrupt malaria transmission in endemic areas. Thus prompted, the Eighth World Health Assembly (1955) resolved that the WHO should spearhead a programme for the global eradication of malaria. The resolution was informed by mounting evidence that anopheline mosquitoes were developing resistance to DDT in parts of the world where malaria control programmes had already been implemented, and a desire to achieve worldwide eradication before insecticide resistance became general or widespread (Wright, et al., 1972).

Phases and progress of the campaign

For a given malarious country or region, the eradication campaign was implemented in four phases: (a) preparatory phase, characterised primarily by geographical reconnaissance and staff training; (b) attack phase, with total coverage spraying of insecticides (DDT and, later, other insecticides); (c) consolidation phase, during which total coverage spraying ceased and surveillance was carried out; and (d) maintenance phase from the time malaria was eliminated. In addition, anti-larval measures such as marsh draining were used to restrict mosquito breeding grounds, while improved therapeutic and prophylactic drugs were also administered.

By 1959, elimination programmes had been launched in 60 of the 148 countries and territories that were classified as malarious, with a further 24 undertaking necessary preparatory work for the launch of elimination initiatives (Figure 5.15). Some indication of the subsequent progress of the eradication campaign can be gained from Figure 5.16. Between 1959 and 1970, the total population of areas classified in the maintenance phase (malaria eliminated) of the programme grew from ~280 million to ~710 million while, in any given year, a further 500–700 million were resident in areas classified within the consolidation and attack phases (Wright, et al., 1972). Although issues of the feasibility of eradication resulted in the exclusion of most countries of sub-Saharan Africa from the global campaign, large tracts of subtropical Asia and Latin America were all but free of infection by 1965 (Learmonth, 1988; Trigg and Kondrachine, 1998).

Figure 5.15 The global campaign to eradicate malaria, 1955–69. Poster prepared by the Malaria Eradication Programme, India, c. 1960. The image, which depicts a man spraying insecticide on a larger-than-life mosquito, captures the main strategy of the Global Malaria Eradication Programme in the 1950s and 1960s: the use of DDT and other insecticides to rid the world of malaria mosquitoes.

Figure 5.15
The global campaign to eradicate malaria, 1955–69. Poster prepared by the Malaria Eradication Programme, India, c. 1960. The image, which depicts a man spraying insecticide on a larger-than-life mosquito, captures the main strategy of the Global Malaria Eradication Programme in the 1950s and 1960s: the use of DDT and other insecticides to rid the world of malaria mosquitoes.

Source: courtesy of the US National Library of Medicine, History of Medicine Division. Copyright owner not known.

Figure 5.16 Annual distribution of population in areas originally classified as malarious, by phase of the WHO Global Malaria Eradication Programme, 1959–1970. The category ‘no eradication activities’ includes countries with anti-malaria activities that were not classified as eradication operations.

Figure 5.16
Annual distribution of population in areas originally classified as malarious, by phase of the WHO Global Malaria Eradication Programme, 1959–1970. The category ‘no eradication activities’ includes countries with anti-malaria activities that were not classified as eradication operations.

Source: redrawn from Cliff, Smallman-Raynor, Haggett, et al. (2009, Figure 4.33, p. 246), originally from Wright, et al. (1972, Figure 1, [link]).

The termination of the eradication programme

By the late 1960s, a number of technical and other obstacles to the global eradication of malaria had become apparent. These obstacles included the emergence of substantial vector resistance to DDT and other chlorinated hydrocarbons (Figure 5.17), the development of drug-resistant strains of the malaria parasite, logistic difficulties relating to both manpower and the accessibility of areas for insecticide spraying, along with a broad array of other technical, administrative, financial and political issues. In 1969, the Twenty-second World Health Assembly re-examined the eradication strategy, with the conclusion that the aims of the programme should be switched from eradication to control. The effective ending of the malaria eradication initiative resulted in a considerable reduction in financial support for anti-malaria programmes, with the problems compounded by the rise in price of insecticides and anti-malaria drugs with the world economic crisis of the early 1970s (Bruce-Chwatt, 1987; Trigg and Kondrachine, 1998). The epidemic rebound that followed on these developments is illustrated for one country (India) in Figure 5.18.

Figure 5.17 Documented resistance to chlorinated hydrocarbon insecticides (DDT group and HCH-dieldrin group) in malaria vectors by 1970. Countries in which vector resistance had been detected (circles) are shown against the global distribution of malaria transmission at the onset of the eradication initiative (shading). Resistant Anopheles species in a given country are named.

Figure 5.17
Documented resistance to chlorinated hydrocarbon insecticides (DDT group and HCH-dieldrin group) in malaria vectors by 1970. Countries in which vector resistance had been detected (circles) are shown against the global distribution of malaria transmission at the onset of the eradication initiative (shading). Resistant Anopheles species in a given country are named.

Source: redrawn from Cliff, Smallman-Raynor, Haggett, et al. (2009, Figure 4.35, p. 250), based on information in Wright, et al. (1972).

Figure 5.18 The resurgence of malaria in India, 1965–76. Maps (A)–(E) plot the annual parasite index (number of malaria cases per 1,000 population per year) by malaria control area for sample years. The annual incidence of malaria in India is plotted in graph (F). From residual foci of disease activity in central, northeastern and western parts of India in 1965, the map sequence displays a spatial resurgence of malaria activity that, in the words of Chapin and Wasserstrom (1983, p. 273), constituted a “major ecological disaster”. Widespread tolerance to organochlorines in some important malaria vectors has been identified as one of the factors that contributed to the resurgence (Chapin and Wasserstrom, 1983; Learmonth, 1988; Sharma, 1996).

Figure 5.18
The resurgence of malaria in India, 1965–76. Maps (A)–(E) plot the annual parasite index (number of malaria cases per 1,000 population per year) by malaria control area for sample years. The annual incidence of malaria in India is plotted in graph (F). From residual foci of disease activity in central, northeastern and western parts of India in 1965, the map sequence displays a spatial resurgence of malaria activity that, in the words of Chapin and Wasserstrom (1983, p. 273), constituted a “major ecological disaster”. Widespread tolerance to organochlorines in some important malaria vectors has been identified as one of the factors that contributed to the resurgence (Chapin and Wasserstrom, 1983; Learmonth, 1988; Sharma, 1996).

Source: redrawn from Cliff, Smallman-Raynor, Haggett, et al. (2009, Figure 4.34, p. 248), based on Learmonth (1988, Table 10.1 and Figure 10.9, pp. 210, 212–[link]).

Recent Global Initiatives: The Roll Back Malaria Partnership

Action against malaria has been ramped up in recent years. In 1998, the Roll Back Malaria Partnership (RBM) was launched by the WHO, UNICEF, UNDP and the World Bank with the purpose of coordinating the global response to malaria. The Partnership launched the Global Malaria Action Plan (GMAP) in 2008 as “a blueprint for the control, elimination and eventual eradication of malaria”, with the specific objective of reducing the number of preventable deaths from malaria worldwide to “near zero by 2015” and with the overall vision of a ‘world free from the burden of malaria’ (World Health Organization, 2011e, [link]) (Figure 5.19). Malaria control also forms a key target of the UN Millennium Development Goal 6 – to halt and to begin to reverse the incidence of malaria and other major diseases by 2015 (Target 6.C). As we describe in the following section, malaria is not deemed to be eradicable with current technology, although there are aspects of its occurrence that are susceptible to elimination.

Figure 5.19 The Roll Back Malaria Partnership. (Left) The Roll Back Malaria Partnership was formed in 1998 as the global framework for implementing coordinated action against malaria. This promotional poster shows a man holding a long-lasting insecticidal net (LLIN), treated with insecticide and designed to be draped over a bed to protect the user against malaria mosquitoes. (Right) Treated bed nets form a key element in efforts to control malaria transmission in endemic areas.

Figure 5.19
The Roll Back Malaria Partnership. (Left) The Roll Back Malaria Partnership was formed in 1998 as the global framework for implementing coordinated action against malaria. This promotional poster shows a man holding a long-lasting insecticidal net (LLIN), treated with insecticide and designed to be draped over a bed to protect the user against malaria mosquitoes. (Right) Treated bed nets form a key element in efforts to control malaria transmission in endemic areas.

Source: World Health Organization (www.who.int).

5.5 Prospects for Future Eradication

International Task Force for Disease Eradication (ITFDE)

The ITFDE was established in 1988 by a grant from the Charles A. Dana Foundation to the Carter Center at Emory University, Atlanta, with the remit of evaluating diseases as potential candidates for future eradication. Following the cessation of funding in the 1990s, the group was reconstituted with the support of the Bill and Melinda Gates Foundation in 2000. By April 2008, the ITFDE had conducted detailed assessments of 34 infectious diseases. Endorsing existing WHO target diseases for global eradication, the ITFDE concluded that seven diseases (dracunculiasis, lymphatic filariasis, measles, mumps, poliomyelitis, rubella and taeniasis/cysticercosis) were eradicable or potentially eradicable with current technology, while aspects of a further eight diseases could be eliminated (Table 5.11). The remaining 19 diseases were variously deemed by the ITFDE not to be eradicable under the present circumstances (e.g. diphtheria, tuberculosis and yellow fever) or not to be eradicable (e.g. African trypansomiasis and Buruli ulcer) (Table 5.12).

Table 5.11 International Task Force for Disease Eradication: candidate diseases for eradication or elimination (status: April 2008)

Disease

Annual toll worldwide

Chief obstacles to eradication

Conclusion

Eradicable and potentially eradicable diseases

Dracunculiasis

<10,000 infected; few deaths

Sporadic insecurity

Eradicable

Lymphatic filariasis

120 million cases

Weakness of primary healthcare systems in Africa; increased national/international commitment needed

Potentially eradicable

Measles

780,000 deaths

Lack of suitably effective vaccine for young infants; cost; public misconception of seriousness

Potentially eradicable

Mumps

Unknown

Lack of data on impact in developing countries; difficult diagnosis

Potentially eradicable

Poliomyelitis

2,000 cases of paralytic disease; 200 deaths

Insecurity; low vaccine coverage; increased national commitment needed

Eradicable

Rubella

Unknown

Lack of data on impact in developing countries; difficult diagnosis

Potentially eradicable

Taeniasis/cysticercosis

50 million cases; 50,000 deaths

Demonstration of elimination on national scale

Potentially eradicable

Diseases/conditions of which some aspects could be eliminated

American trypanosomiasis

10–12 million infections

Difficult diagnosis, treatment; animal reservoirs

Not eradicable; can stop vector-borne transmission to humans in some areas

Hepatitis B

250,000 deaths

Carrier state; infections in utero not preventable; need routine infant vaccination

Not now eradicable, but could eliminate transmission over several decades

Malaria

> 300 million cases; > 1 million deaths

National and international commitment; weak primary healthcare systems; drug and insecticide resistance; non-specific diagnoses

Not now eradicacable; elimination possible in Hispaniola

Neonatal tetanus

560,000 deaths

Inexhaustible environmental reservoir

Not now eradicable, but could prevent transmission

Onchocerciasis

37–40 million cases; 340,000 cases of blindness

Lack of macrofilaricide and test for living adult worms

Could eliminate associated blindness in Africa, and probably transmission in the Americas

Rabies

52,000 deaths

No effective way to deliver vaccine to wild animals that carry the disease

Could eliminate urban rabies

Trachoma

150 million cases; 6 million cases of blindness

Link to poverty; inadequate rapid assessment methodology and diagnostic test for ocular infection

Could eliminate associated blindness

Yaws and other endemic treponematoses

Unknown

Lack of political will; inadequate funding; weaknesses in primary healthcare systems

Could eliminate transmission nationwide, as illustrated by India

Source: information from Centers for Disease Control and Prevention (1993b, Table 3, [link][link]) and the International Task Force for Disease Eradication (www.cartercenter.org).

Table 5.12 International Task Force for Disease Eradication: diseases deemed not to be eradicable (status: April 2008)

Disease

Annual toll worldwide

Chief obstacles to eradication

Diseases that are not eradicable under the present circumstances

Ascariasis

1 billion infections; 20,000 deaths

Eggs viable in soil for years; laborious diagnosis; widespread

Cholera

Unknown

Environmental reservoirs; strain differences

Diphtheria

Unknown

Difficult diagnosis; multiple-dose vaccine

Hookworm disease

740 million cases; 10,000 deaths

Increased national and international commitment; monitoring impact of interventions

Leprosy

225,000 cases

Need for improved diagnostic tests and chemotherapy; social stigma; potential animal reservoir

Meningococcal meningitis

614,000 cases; 180,000 deaths

Lack of serogroup A conjugate vaccine; cost

Pertussis

40 million cases; 400,000 deaths

High infectiousness; early infections; multiple-dose vaccine

Rotaviral enteritis

80 million cases; 870,000 deaths

Inadequate vaccine

Schistosomiasis

200 million infections

Reservoir hosts; increased snail-breeding sites; need simple diagnostic test for intestinal disease

Tuberculosis

8–10 million new cases; 2–3 million deaths

Need for improved diagnostic tests, chemotherapy and vaccine; wider application of current therapy

Visceral leishmaniasis

500,000 cases

Inadequate surveillance, drug supply and knowledge of vector breeding sites; weak primary healthcare systems

Yellow fever

> 10,000 deaths

Sylvatic reservoir; heat-labile vaccine

Diseases that are not eradicable

African trypanosomiasis

300,000–600,000 infections

Reservoir hosts; difficult treatment and diagnosis

Amoebiasis

500 million cases; 40,000–110,000 deaths

Asymptomatic infections; difficult diagnosis, treatment

Bartonellosis

Unknown

Asymptomatic infections; difficult diagnosis, treatment

Buruli ulcer

Unknown

Inadequate surveillance, early detection and treatment; need field diagnostic test and orally administered treatment

Clonochiasis

Unknown (20 million cases in China)

Animal reservoir; asymptomatic infections; carrier state

Enterobiasis

Unknown

Widespread; mild disease

Varicella zoster

Unknown (3 million cases in USA)

Latency of virus; inadequate vaccine

Source: information from Centers for Disease Control and Prevention (1993b, Table 3, [link][link]) and the International Task Force for Disease Eradication (www.cartercenter.org).

Regional Elimination Campaigns: Measles

In addition to those infectious diseases listed in Table 5.2 that are subject to ongoing global eradication campaigns, concerted action against a number of other diseases (including lymphatic filariasis, malaria, measles, onchocerciasis and yaws) has resulted in their retreat from large areas of the globe. Of these diseases, special attention has focused in recent years on measles as a potential candidate for global eradication.

The Regional Elimination of Measles

Prior to the widespread availability of measles vaccine in the world’s poorer countries, an estimated 2.6 million people died of the disease each year. This situation changed as the WHO’s Expanded Programme on Immunization (EPI) was rolled out from the 1970s and 1980s (Section 4.4). Between 1980 and 2010, the annual number of notified measles cases worldwide fell from 4.21 million to 0.33 million – a decline that was accompanied by a similarly sharp reduction in the WHO’s estimates of global measles deaths. Five of the WHO Regions have used these developments as a springboard for regional elimination initiatives. In 1994, the WHO Americas Region established the target of eliminating measles from the Western Hemisphere by 2000. Similar elimination initiatives have subsequently been established in the WHO Regions of Europe (elimination target date: 2010), Eastern Mediterranean (2010), Western Pacific (2012) and Africa (2020), with only South-East Asia having yet to establish a target date for elimination.

Progress towards the WHO regional elimination goals is illustrated in Figures 5.20 and 5.21. The elimination of measles in the Americas was achieved in 2002, albeit with subsequent small outbreaks associated with measles virus importations. Major setbacks to measles elimination have been encountered elsewhere, however, including numerous and prolonged outbreaks of measles in Africa and Europe and the continued high burden of the disease in some parts of South-East Asia. These developments have been attributed to sub-optimal coverage with measles-containing vaccine (see, for example, Section 4.6) and to the deleterious impact of funding gaps on vaccination campaigns (Bellini and Rota, 2011).

Figure 5.20 Measles trends in the WHO regions. Annual count of notified cases of measles in each WHO region, 1980–2010. See Figure 2.31 for a map of the regions.

Figure 5.20
Measles trends in the WHO regions. Annual count of notified cases of measles in each WHO region, 1980–2010. See Figure 2.31 for a map of the regions.

Source: data from the World Health Organization (www.who.int).

Figure 5.21 World maps of measles incidence. Maps plot the average annual count of measles cases reported by WHO member states. (A) 1991–95. (B) 2006–10.

Figure 5.21
World maps of measles incidence. Maps plot the average annual count of measles cases reported by WHO member states. (A) 1991–95. (B) 2006–10.

Source: data from the World Health Organization (www.who.int).

Integrated approaches: measles and rubella elimination in the Americas

In the drive to eliminate measles from the Americas, the Pan American Health Organization (PAHO) recommended that measles vaccines should also contain rubella antigen. In September 2003, having successfully interrupted the indigenous transmission of measles virus, PAHO adopted a target for the regional elimination of rubella by 2010. The rubella elimination strategy has used a combined measles-rubella vaccine, with the dual function of increasing population immunity to rubella virus whilst maintaining high levels of immunity to measles virus. The last endemic case of rubella in the Americas was detected in 2009 (Andrus, et al., 2011) (Figure 5.22).

Figure 5.22 The elimination of measles (sarampión) and rubella (rubéola) in the Americas. (Left) Pan American Health Organization poster, “Borders free from measles and rubella.” (Right) Cuban Ministry of Health poster, “Consolidating the elimination of measles and rubella in Cuba, 2007.” Cuba had eliminated measles in 1993 and rubella in 1995 through the implementation of routine vaccination and two mass vaccination campaigns in 1985 and 1986 that targeted children, adolescents and adults. In response to a mumps outbreak, a vaccination campaign with measles, mumps and rubella (MMR) vaccine was launched in 2007. Coverage of the target group (males and females aged 12–24 years) was 97 percent and contributed to the maintenance of measles and rubella elimination. The lower graph relates to rubella and shows vaccination coverage (line trace, right-hand axis) and the number of reported cases (bar graph, left-hand axis).

Figure 5.22
The elimination of measles (sarampión) and rubella (rubéola) in the Americas. (Left) Pan American Health Organization poster, “Borders free from measles and rubella.” (Right) Cuban Ministry of Health poster, “Consolidating the elimination of measles and rubella in Cuba, 2007.” Cuba had eliminated measles in 1993 and rubella in 1995 through the implementation of routine vaccination and two mass vaccination campaigns in 1985 and 1986 that targeted children, adolescents and adults. In response to a mumps outbreak, a vaccination campaign with measles, mumps and rubella (MMR) vaccine was launched in 2007. Coverage of the target group (males and females aged 12–24 years) was 97 percent and contributed to the maintenance of measles and rubella elimination. The lower graph relates to rubella and shows vaccination coverage (line trace, right-hand axis) and the number of reported cases (bar graph, left-hand axis).

Source: Castillo-Solórzano, et al. (2009, unnumbered plates, [link], [link]).

Accelerated Measles Control and Eradication

The Measles Initiative was established in 2001 as a collaborative effort of the WHO, UNICEF, the American Red Cross, the United States Centers for Disease Control and Prevention (CDC) and the United Nations Foundation to support governments and communities in the implementation of measles vaccination campaigns and surveillance (Figure 5.23). With an effective global partnership in place, the Sixty-third World Health Assembly resolved in May 2010 to move towards the eventual eradication of measles. Although no date for the eradication of the disease was set, the Assembly did endorse a series of targets to be realised by 2015 for accelerated measles control. These targets include: > 90 percent coverage with a first dose of measles-containing vaccine at the national level, and > 80 percent coverage at the regional level; reduction of annual measles incidence to < 5 cases per million with this level to be maintained; and, within the framework of Millennium Development Goal 4 (MDG 4 – to reduce child mortality), to reduce measles mortality by 95 percent as compared with estimated levels for 2000 (Bellini and Rota, 2011).

Figure 5.23 Poster for the Measles Initiative. The Measles Initiative was established in 2001 as a collaborative effort of the WHO, UNICEF, the American Red Cross, the United States Centers for Disease Control and Prevention (CDC) and the United Nations Foundation to promote the global control of measles.

Figure 5.23
Poster for the Measles Initiative. The Measles Initiative was established in 2001 as a collaborative effort of the WHO, UNICEF, the American Red Cross, the United States Centers for Disease Control and Prevention (CDC) and the United Nations Foundation to promote the global control of measles.

Source: Castillo-Solórzano, et al. (2009, unnumbered plate, [link]).

Feasibility of global measles eradication

Although measles does not share all the criteria of the smallpox eradication ‘model’ (Table 5.5), the feasibility of global measles eradication is endorsed by the ITFDE (Table 5.11). Humans are the sole reservoir of the virus; accurate diagnostic tests for measles virus infection exist; and an effective and affordable intervention (vaccine) is available (Bellini and Rota, 2011; Moss and Strebel, 2011). The elimination of measles from the Americas has demonstrated the programmatic and operational feasibility of the interruption of measles virus transmission over large geographical areas (Figures 5.20 and 5.21), while economic and health system analyses also validate the feasibility of measles eradication. To these criteria can be added the broad platform of support that has already been established for an eradication initiative (World Health Organization, 2010b; Keegan, et al., 2011). The principal challenges to measles eradication are likely to be logistical, political and financial, with rapid urbanisation and increasing population density, wars and conflicts serving as major obstacles (Keegan, et al., 2011; Moss and Strebel, 2011).

5.6 Hostile Threats: Disease Eradication and Bioterrorism

Once a disease agent has been eradicated, strategies are required to minimise the risk of the reintroduction of the agent into the human population. Recognising that certain international terrorist groups have a declared intent to develop unconventional (Chemical, Biological, Radiological and Nuclear or CBRN) weapon capabilities, the identification of bioterrorism as one of the foremost risks for national and global security has highlighted the threat that attaches to the deliberate release of disease agents (Morens, et al., 2004). Although a large number of viral, bacterial and other disease agents have been posited as possible agents for biological weapons and bioterrorist attacks (World Health Organization, 2004e), a series of factors (including cultivation and effective dispersal, transmission dynamics, environmental stability, infectious dose size and availability of prophylactic and therapeutic measures) suggests that relatively few agents have strategic potential. Among these, smallpox (variola) virus has received particular attention in the literature (Smallman-Raynor and Cliff, 2004).

Smallpox

The Emergency Preparedness and Response (EPR) Program of the US Centers for Disease Control and Prevention (CDC) classifies variola major virus (smallpox) alongside Bacillus anthracis (anthrax), Clostridium botulinum toxin (botulism), Yersinia pestis (plague), Francisella tularensis (tularemia) and the viruses associated with certain haemorrhagic fevers (Ebola, Lassa, Machupo and Marburg) as Category A agents for use in biological attacks (Centers for Disease Control and Prevention, 2008). These agents are considered to pose a high-priority risk to national security because they can be easily disseminated or transmitted from person-to-person; they can result in high mortality rates; they have the potential for major public health impacts that might cause public panic and social disruption; and they require special action for public health preparedness.

Particular concern attaches to variola major virus as a Category A biological weapons agent on account of the status of smallpox as an eradicated disease. Routine vaccination against smallpox ceased on the eradication of the disease in the late 1970s, and global immunity has consequently waned in the ensuing years. Under such circumstances, smallpox bioweapons have the potential to spark pandemic transmission of the viral agent, even more so given the lack of familiarity with the disease among recent generations of physicians.

Planning for a Deliberate Smallpox Release: The United Kingdom

In the United Kingdom, guidelines for smallpox response and management in the event of a deliberate smallpox release were published by the Department of Health in 2003. The guidelines detail the establishment of nine Regional Smallpox Diagnosis and Response Groups (RSDRGs) in England, one for each public health region, and one each for Scotland, Northern Ireland and Wales. The groups are headed by a Regional Epidemiologist, with each group having at least five Smallpox Management and Response Teams (SMART) to respond to suspected and probable cases of smallpox. Designated Smallpox Care Centres will provide observation and treatment facilities for suspected and confirmed cases. Designated Smallpox Vaccination Centres will deliver vaccine to target groups while, to assist the implementation of vaccination strategy and other actions, a six-level system of smallpox alert has been established (Figure 5.24).

Figure 5.24 Alert levels for a deliberate release of smallpox virus in the United Kingdom. The Department of Health’s Guidelines for Smallpox Response and Management in the Post-Eradication Era (2003) identify six levels of alert in the event of a deliberate release of smallpox, with each level associated with a specific vaccination strategy and other actions to contain and control the event. Vaccination activities at Levels 0 and 1 centre on the maintenance of immunity in key healthcare workers and other personnel. Levels 2 and 3 are associated with the implementation of ring vaccination strategies in outbreak-affected areas (Section 4.3 Vaccination Strategies and Disease Control4.3). If ring vaccination fails to control the outbreak, Level 4 marks the possible implementation of mass vaccination. Finally, Level 5 is associated with the continuing maintenance of immunity in key healthcare workers and other personnel in the post-outbreak period.

Figure 5.24
Alert levels for a deliberate release of smallpox virus in the United Kingdom. The Department of Health’s Guidelines for Smallpox Response and Management in the Post-Eradication Era (2003) identify six levels of alert in the event of a deliberate release of smallpox, with each level associated with a specific vaccination strategy and other actions to contain and control the event. Vaccination activities at Levels 0 and 1 centre on the maintenance of immunity in key healthcare workers and other personnel. Levels 2 and 3 are associated with the implementation of ring vaccination strategies in outbreak-affected areas (Section 4.3). If ring vaccination fails to control the outbreak, Level 4 marks the possible implementation of mass vaccination. Finally, Level 5 is associated with the continuing maintenance of immunity in key healthcare workers and other personnel in the post-outbreak period.

Source: redrawn from Smallman-Raynor and Cliff (2012, Figure 11.21, [link]), based on Department of Health (2003).

Control under different transmission scenarios

Spatial forecasts of smallpox transmission from initial seedings in the vicinity of central London, generated for three representative scenarios (low, medium and high) of the average number of secondary infections generated by an infected person in a susceptible population, are provided by Riley and Ferguson (2006) (Figure 5.25, located in the colour plate section). Their results imply that rapid isolation of cases on presentation of rash would be sufficient to bring low- and medium-transmission scenarios under control. Regional or national mass vaccination would only need to be considered for the highest transmission scenarios. A rather different problem would arise if the smallpox release occurred elsewhere in the world and the virus spread to the United Kingdom as a result of multiple independent importations that were dispersed over time. Under such circumstances, mass vaccination may become a more attractive scenario.

Figure 5.25. Smallpox and bioterrorism. The maps show the predicted spread of smallpox following a deliberate release in the vicinity of central London. They give the average number of cumulative infections per square kilometre during the first 75 days of the outbreak under (A) low, (B) medium, and (C) high transmission scenarios. Simulations suggest that case isolation and contact tracing with vaccination would cause rapid cessation of virus transmission under most scenarios. The costs of mass vaccination should only be contemplated at the highest end of the transmission scenarios.

Figure 5.25.
Smallpox and bioterrorism. The maps show the predicted spread of smallpox following a deliberate release in the vicinity of central London. They give the average number of cumulative infections per square kilometre during the first 75 days of the outbreak under (A) low, (B) medium, and (C) high transmission scenarios. Simulations suggest that case isolation and contact tracing with vaccination would cause rapid cessation of virus transmission under most scenarios. The costs of mass vaccination should only be contemplated at the highest end of the transmission scenarios.

Source: redrawn from Smallman-Raynor and Cliff (2012, Figure 11.1, [link]), originally from Riley and Ferguson (2006, Figure 3, p. 12640).

Poliomyelitis

Unlike smallpox, poliomyelitis is not generally viewed as representing an immediate bioterrorist threat because of the currently high levels of immunity to poliovirus. This situation will, however, change with OPV cessation in the post-certification era (Sutter, et al., 2004). While the containment of poliovirus stocks, with a view to limiting both the accidental and intentional release of the virus, forms a central component of the Global Polio Eradication Initiative’s Strategic Plan 2010–2012 (Section 5.3), the ability to synthesise poliovirus from stretches of mail-order DNA on the basis of a genetic blueprint from the Internet (Cello, et al., 2002) has raised fresh concerns over the bioterrorist threat:

As a result of the World Health Organization’s vaccination campaign to eradicate poliovirus, the global population is better protected against poliovirus than ever before. Any threat from bioterrorism will arise only if mass vaccination stops and herd immunity against poliomyelitis is lost. There is no doubt that technical advances will permit the rapid synthesis of the poliovirus genome, given access to sophisticated resources (Cello, et al., 2002, p. 1018).

“The potential for viral synthesis,” Cello, et al. conclude, “is an important additional factor for consideration in designing the closing stages of the poliovirus eradication campaign” (ibid.).

5.7 Towards Extinction

Table 5.3 draws a fundamental distinction between eradication and extinction, the latter term describing the state in which a disease agent no longer exists in nature or the laboratory. To date, only smallpox (variola) virus has reached the status of a disease agent on the brink of extinction.

The Destruction of Known Variola Virus Stocks

WHO-sanctioned stocks of variola virus are currently held in the laboratories of the CDC in Atlanta, USA, and the State Research Centre for Virology and Biotechnology in Koltsovo, Russian Federation. A long-running debate over the ultimate fate of these last known virus stocks has been informed by a range of scientific, political and ethical considerations, with the potentially calamitous consequences of a release – accidental or otherwise – forming one line of argument for their destruction (Butler, 2011; Lane and Poland, 2011). Following a major review of variola virus research by the WHO Advisory Committee on Variola Virus Research (ACVVR) in 2010, the Sixty-fourth World Health Assembly (2011) endorsed the decision of previous Assemblies that existing virus stocks should be destroyed once vital research has been completed. In the light of a further review of variola virus research, a possible date for the destruction of WHO-sanctioned stocks will be considered at the Sixty-seventh World Health Assembly in 2014. While the destruction of these stocks would mark a step towards virus extinction in the terms of Table 5.3, the possible existence of other (undeclared) laboratory stocks of live variola virus cannot be ruled out. The situation is further complicated by the recognition that variola virus, like poliovirus, can be reconstructed in the laboratory from published gene sequences (Lane and Poland, 2011).

5.8 Conclusion

The concept of disease eradication has had a chequered history, occasionally finding favour and then falling into disrepute as a global health strategy over the last 100 years (Table 5.1). Commenting on the eradication concept in the 1990s, the International Task Force for Disease Eradication (ITFDE) observed that

The main obstacle to the concept’s current acceptance is that if the concept of eradication is invoked against inappropriate or unattainable targets, it can be brought into disrepute. The declared targets of ‘elimination’ of neonatal tetanus by 1995 and of leprosy by 2000 are potential examples of such dangers. Care should be taken to reserve use of the terms ‘eradication’ and ‘elimination’ only for carefully chosen diseases that have a high likelihood of being eradicated (Centers for Disease Control and Prevention, 1993b, [link]).

As we have seen in this chapter, the success or otherwise of a global eradication campaign is contingent not only on issues of biological and technical feasibility, but also on issues of economic costs and benefits and, crucially, societal and political commitment. Historically, these criteria have determined the failure of some campaigns (yellow fever, yaws and malaria), the success of others (smallpox) and, on the basis of these past experiences, the judicious selection of target diseases for the future. From the list of potentially eradicable diseases identified by the ITFDE, measles was singled out by the 2010 World Health Assembly as a likely successor to poliomyelitis and dracunculiasis for global eradication. But successful eradication campaigns raise fresh dilemmas. Once a disease has been eradicated, difficult decisions need to be made over the ultimate fate of the remaining laboratory stocks of the associated pathogen – a dimension of disease eradication that the global community has been grappling with in respect of smallpox virus for three decades.