Considerations for Viral Disease Eradication Lessons Learned and Future Strategies: Workshop Summary (2002) / Chapter Skim
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Currently, there are three infectious viral disease candidates for global eradication- polio, measles, and rubella each of which closely satisfies necessary preconditions for eradication as outlined by the 1997 Dahiem Conference on Disease Eradication: (1) no animal reservoir for the virus is known or suspected; (2)
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. Smallpox had a higher average age at infection prior to wide-scale vaccination and thus was less transmissible than either polio or measles.
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As the title of this report suggests, the focus of this workshop was post-era~ication challenges. However, certification of eradication for other infectious diseases besides smallpox may be years off.
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This is best achieved through a two-close immunization strategy: once at nine months of age and then again in the second year of life. Major success in prolonged interruption of measles transmission in the Americas using this two-dose immunization strategy, supplemented with nationwide "catch-up" and "follow-up" campaigns targeting susceptible populations and geographic reservoirs, provides evidence for the feasibility of global eradication.
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Indeed, data from the Americas show that measles transmission can be interrupted on entire continents, which means that interruption is technically possible, given the necessary political commitment. While the United States has made measles eradication a public health priority, some of the lowest measles vaccine coverage rates are found among the world's richest countries, where measles is not seen as a problem.
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vaccine; ant! repeat mass vaccinations clirectect at children nine to fourteen years of age.
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Ideally, a new, non-infectious vaccine that produces mucosal immunity like OPV would be developed as an end-strategy for immunization against polio—perhaps a DNA or some other vectored vaccine—although it is unrealistic to expect either the private or public sector to invest in the development and production of such a vaccine this close to eradication. Different ways of combining OPV and IPV strategies have been considered for use in the post-eradication era, but no decision has been reached about which strategy would offer the best protection against OPV-derived viral disease.
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We have no experience with the consequences of a reintroduction or reemergence of previously eradicated organisms. We do not know how viruses will evolve in the future; if and how current vaccines would be able to protect us from disease caused by newly evolved viral variants; and if and how our immune system may change as the selective pressures previously imposed by eradicated viruses are lifted or altered.
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Bioterrorism is generally considered the greatest risk of smallpox reintroduction, even though it was initially dismissed as a possibility since all countries had actively participated in eradication efforts. By the mid-199Os, however, U.S.
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The creation of new reservoir hosts, cross-species transfer of infectious agents, rise of antimicrobial resistance, and immune evasion are all potential sources for the emergence of novel viral variants. Important and often overlooked, mass vaccination itself can also exert tremendous selective pressures and lead to the evolution of new infectious agents.
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DETECTION AND SURVEILLANCE Continued surveillance, improved surveillance methods, and assistance to lesser developed countries in their efforts to implement national surveillance campaigns are essential for the rapid detection of disease outbreaks. Given the biological variability of vaccine strains, and the innumerable array of samples in frozen storage, it is not a question of whether disease outbreaks will occur in the post-eradication era, but, rather, when and where.
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Ideally, the IHR revision process should involve broad consensus with all WHO member states; better working relationships among WHO, member states, and other international agencies whose work is related to the IHR need to be established. The IHR are a set of global regulatory guidelines for how to respond to international disease threats and are currently the only binding set of regulations established on global surveillance for infectious diseases by WHO member states.
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In anticipation of polio eradication in the early 1990s, for example, polio research laboratories were told they would be soon required to cease poliovirus research and destroy all virus and infectious DNA stocks. The unfortunate consequence was that many research programs that could have contributed valuable information on new vaccines, new antiviral drugs, and animal models for virus transmission were shut down.
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Viral genes could readily be synthesized from nucleic acid sequences, and viruses themselves could probably be reconstituted from sequences or clones, thus precluding the need for continued storage of intact viruses. Importantly, however, individuals or organizations with bioterrorist intentions could do this just as well as legitimate research labs.
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issued a contract for the production of a new national vaccine stockpile in 2000, the vaccine reserve was not only deficient but had clecayed over time. The vaccine program infrastructure had deteriorated; vaccine technology used previously for smallpox vaccine production was outdated; and standards of vaccine production had changed.
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Probiotic bacteria living microbes introduced into the body to improve intestinal microbial balance- have great potential to sustain an immune response in the post-vaccine era and may prove useful in strengthening the immune response in immunocompromised individuals who are at risk for chronic infection. For example, recent studies have shown that probiotic lactobacilli can have a beneficial effect on the immune response in HIV-infected children.
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Drawing on the lessons learned from smallpox eradication and as summarized above and discussed in detail throughout this report, a responsible post-eradication strategy must include provisions for vaccine reserves and contingency planning in case the disease re-emerges; continued surveillance and diagnostic activities; and research on and development of new vaccines and antiviral therapeutic drugs. The federal government will play a key role in supplying these provisions in the
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The intelligence, arms control, law enforcement, and defense communities must be adequately prepared since they are all likely to be involved in the event of a disease outbreak with national security consequences. Intelligence information may be required to help determine if the outbreak was a natural or deliberate occurrence; evidence may need to be collected for legal or arms control issues; recurrence of disease outbreak will need to be prevented; and those responsible will need to be held accountable.
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Too often in the developing world, global eradication priorities override local health priorities. In the polio eradication effort, for example, countries have been pressured to focus on global priorities (to immunize everyone, for example, even if polio is not a disease that the people have witnessed)
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empowering communities with the resources to address their own problems in a self-reliant way is the best framework for clearing with disease outbreaks in a post-eradication era. However, building local health infrastructure does not necessarily mean implementing the "cloc-in-the-box" western model of primary health care centers.
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With respect to polio eradication efforts, for example, a major selling point to political leaders was the potential post-eradication cost savings. But if we had known that immunization would likely need to be continued even in the post-eradication era, would the level of political commitment have been the same?
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Director, Division of Vaccines and Immunization Pan American Health Organization, Washington, D.C. HISTORY AND PROSPECTS FOR DISEASE ERADICATION The concept of "disease eradication" originated in the late 18th century, when Edward lenner inoculated lames Phipps with the cowpox virus and subsequently infected him with the lethal smallpox virus.
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Eradication: the absence of a disease agent in nature in a defined geographic area; control measures can be discontinued once the risk of importation of the agent is no longer present; · Extinction: the specific disease agent no longer exists in nature or the laboratory. With these definitions, the term eradication can be used in different geographic levels, such as "eradication of a disease in a given area or country," "eradication from a region or regions of the world," and, ultimately, the "eradication of a disease globally." PRECONDITIONS FOR DISEASE ERADICATION Several preconditions must be met before eradication can be considered.
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Smallpox eradication was an extraordinary initiative which set the example for future disease eradication programs. The smallpox eradication program was initially based on the premise that mass vaccination campaigns would stop transmission, but the program managers soon recognized that this strategy was not sufficient to achieve the objective.
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LESSONS FROM RECENT EXPERIENCES: POLIO AND MEASLES ERADICATION IN THE AMERICAS The lessons learned from smallpox eradication were subsequently applied to the Pan American Health Organization (PAHO) initiatives to eraclicate both poliomyelitis and measles from the Americas.
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Third, as the program was winding down in Brazil, an outbreak of poliovirus type-3 was cletected. Analysis of the outbreak indicated that the composition of the trivalent vaccine did not contain adequate quantities of poliovirus type-3; therefore, the manufacturers were asked to reformulate the vaccine.
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Disease outbreaks occurred every one and a half to two years, as new cohorts of susceptible children were introduced into the population. As the outbreaks occurred, the population of susceptibles diminished and the disease subsided, until a new cohort of susceptibles again fueled transmission of the infectious agent.
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These "keep-up" vaccination programs generally target 90-95 °/O coverage.
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It has also accelerated control of other diseases, such as neo-natal tetanus, and the launching of other disease eradication initiatives. For example, at the end of the first day of polio immunizations cluring the three-day campaign to halt the vaccinederived polio outbreak in the Dominican Republic in December 2000, the government of the Dominican Republic realized that there would be vaccine shortage in view of the high campaign turn-out.
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A final lesson from the polio and measles eradication efforts in the Americas is that the polio eradication effort in particular had a very positive impact on strengthening the health systems/services infrastructure. This is well documented by a study conducted in several countries in the Americas by the Commission on the Impact of the Expanded Program on Immunization and the Polio Eradication Initiative on Health Systems in the Americas, chaired by Dr.
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Plus, the health infrastructure among developing countries is not strong enough to maintain high vaccination coverage in all birth cohorts, which means that the required frequency of mass immunization campaigns is high and the associated cost enormous. CONCLUSION The global eradication of smallpox, the eradication of poliomyelitis from the Americas and its near-global eradication, and the near-eradication of measles from the Americas demonstrate the tremendous progress achieved in disease eradication efforts.
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1998. The Eradication of Infectious Diseases (Report of the Dahlem Workshop on the Eradication of Infection Diseases, Berlin, March 16-22, 1997)
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