Considerations for Viral Disease Eradication Lessons Learned and Future Strategies: Workshop Summary (2002) / Chapter Skim
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2 Major Efforts for Disease Eradication
2 Major Efforts for Disease Eradication
Pages 33-63
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From page 33... ...
Data from the Americas show that measles transmission can be interrupted on entire continents; thus, eradication is technically feasible. Lack of sufficient political will is probably the greatest impediment to global measles eradication.
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From page 34... ...
Likewise, eradication of rubella by correct application of a measiesrubella or measles-mumps-rubella vaccine is feasible. However, a major challenge to congenital rubella syndrome (CRS)
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There were many factors that uniquely favored smallpox eradication: . No other disease has features that made diagnosis and surveillance for infection so easy.
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From page 36... ...
In 1967, when the global smallpox campaign began, there were a number of Latin American, east Asian, and African countries where smallpox transmission had been stopped. This was due in large part to the use of the air-dried vaccine or a new freeze-ctried product developed in the early 1950s.
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From page 37... ...
A major concern following eradication was the possible reintroduction of smallpox virus from a laboratory. Limiting the number of laboratories that retained smallpox virus was considered an important step in mitigating the risk of this occurring.
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In 1994, the TRIO Orthopoxvirus Committee, in a report to the Director General, recommended that the 1995 WHA pass a resolution calling for the destruction of all remaining stocks of smallpox virus in June 1995. By that time, representative strains of variola virus had been prepared as a cloned fragment library and sequenced.
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From page 39... ...
Moreover, experience has shown that failed eradication programs in most areas, although resulting in better control while special measures are in place, gradually revert to a pre-eradication status as special funds and interest fade. For sometime after the declaration of eradication, the only likely sources for the reintroduction of smallpox virus were from victims exhumed from the tundra or escape from the laboratory.
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From page 40... ...
Decides to authorize temporary retention up to not later than 2002 and subject to annual review by the World Health Assembly of the existing stocks of variola virus..." · It was evident during the smallpox program that a failed eradication effort could have serious repercussions for other global initiatives. Financial support for smallpox eradication was problematic throughout its course, largely because of a failed WHO-sponsored global malaria eradication program after the investment of more than $2 billion.
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From page 41... ...
Humans Critical for Transmission Humans are critical to the maintenance of measles virus transmission; humans are the only reservoir for measles virus, and virus survival in the environment is limited to several hours. The major cell receptor for measles virus, CD46, is found only in primate cells (and in transgenic laboratory animals)
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From page 42... ...
Failure to Prevent Transmission with a Single Dose Based on seroconversion and clinical effectiveness studies, a single dose of measles vaccine administered in the second year of life induces immunity in about 95°/0 of vaccinees. In the developing world, persistent transmission of measles virus and high infant morbidity and mortality have led to the recommendation that infants be vaccinated at nine months of age, even
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From page 43... ...
In recent years, major successes in measles elimination the interruption of indigenous measles transmission but with continued vaccination activities due to the threat of imported cases from large geographic areas suggest that global eradication is feasible. Because of its potential for eradication and because global eradication efforts would protect against measles importation, the United States has made measles a global health priority.
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There is optimism that the newly formed Global Alliance for Vaccines and Immunization will increase funding for measles vaccination coverage. Supplemental measles vaccination campaigns are increasingly being used to supplement routine immunization services and eliminate the buildup of susceptible populations.
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45 Percent coverage a)
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From page 46... ...
The African Region reported a routine vaccination coverage of 49°/0 in 1998, when an estimated 500,000 children died from measles. Efforts to accelerate measles control have been conducted since the mid-199Os and include: mass vaccination campaigns usually targeting children between nine months and five years of age; vitamin A supplementation administered on polio National Immunization Days (NIDs)
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From page 47... ...
47 Routine infant vaccination coverage o 0 0 0 0 0 oo ~ ~ c~ 0 L I I I 1 1 \ ~n ._ CO Q C' Q C' Cd 1 l O O O O o O O O O _ O O O O ~) O CO C~ C\l cn ._ Q o IL saseo pawJ!
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From page 48... ...
In contrast, PAHO-style nationwide campaigns which reach previously unvaccinated children are highly effective at interrupting measles transmission. They should be repeated at regular intervals and integrated with routine immunization services.
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However, none of these cities have the population density seen in cities like Bombay, Jakarta, and Lagos, all of which have population densities that are more than three times that of Mexico City. Thus, it remains to be demonstrated whether the immunity levels achieved through the PAHO mass campaigns using existing measles vaccines are capable of eliminating transmission in the population-dense urban areas of Africa and Asia.
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Measles eradication will require that the developed world realize that measles disease is worth preventing in their own countries so that they do not become reservoirs of the virus. Further, successful eradication will require the developed world to help finance developing country efforts.
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· The measles virus and potentially infectious materials would need to be contained in the laboratory (based on how the poliovirus was biocontained)
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Nevertheless, the available scientific and programmatic information is encouraging, and we believe someday there will be a goal of measles eradication. Meanwhile, the regional efforts to eliminate measles should be supported, and research should be encouraged to address the potential impediments to global eradication of measles.
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From page 53... ...
Avidity determinations on IgG antibody is another useful diagnostic tool but it can only be performed in sophisticated laboratories and it is not well suited to public health uses. Thus, the most sensitive diagnostic techniques are not suited to or available for field use, and diagnoses often rely on clinical criteria.
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From page 54... ...
In one study (Best et al., 1987) , 70% of seronegatives challenged with rubella virus developecl viremia, and 100% developed viral excretion; 0°/O of seropositive and vaccinated individuals developed viremia, and 5% of seropositive and vaccinated individuals developed viral excretion.
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Immunization rates are increasing in the eastern Mediterranean, Southeast Asia, and western Pacific regions. However, the worId's two most populous countries, India and China, do not use rubella vaccine routinely, nor do Africa and large parts of Asia.
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From page 56... ...
Nonetheless, potential eradication efforts face several challenges: · Although the administration cost would be the same, adding the mumps andlor rubella components to the measles vaccine would increase the price of the vaccine to approximately 30 to 50 cents per dose. · Vaccine supply needs to meet demand, which would require encouraging manufacturers to increase production, and also would lead to .
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Instead, Sabin proposed mass OPV immunization, which has proven to be the most effective strategy for the control of poliomyelitis epidemics in the developing world Cabin, 19851. Global eradication is the natural outcome.
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From page 58... ...
Much work remains to be done to mop up poliovirus types 1 and 3 in the Middle East and southeast Asia and Africa, especially in areas of civil conflict and in countries with weak or non-existent health infrastructure. The goal of eradication by 2000 was not met, but the original goal of certifying the world as polio-free by 2005 may still be within reach.
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From page 59... ...
Each of these three criteria is addressed below. Assurance of eradication' The world will be certified polio-free when the Global Commission for the Certification of Polio Eradication is satisfied that all six Regional Commissions and their national committees have provided adequate data to document the absence of wild poliovirus transmission after at least three years of high-quality post-eradication surveillance (WHA, 1988~.
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From page 60... ...
In December 1999, WHO published the WHO Global Action Plan for Laboratory Containment of Wild Polioviruses (WHO, 1999; ~WHO, 2000~. The first step in this wiclely reviewed plan requires that each nation survey all laboratories that may possess wild poliovirus infectious or potentially infectious materials, encourage the disposition of unneeded materials, and prepare a national inventory of all laboratories that retain such materials.
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From page 61... ...
Maintaining adequate vaccine coverage levels will not be easy in the absence of wild poliovirus, during a time of changing public perception of OPV risk/benefits, and in an era of decreased international funding. Option 2, stopping OPV after synchronized global immunization days, is based on the observations in Cuba and elsewhere that circulation of OPV strains ceases in a well-immunized population about three months after the last NID (PAHO, 1985~.
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From page 62... ...
Rubella and congenital rubella syndromeUnited States, 1994-1997. Morbidity and Mortality Weekly Report 46(16)
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From page 63... ...
2000. Guidelines for Implementing the Pre-Eradication Phase of the Global Action Plan for Laboratory Containment of Wild Polioviruses.
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