The role of surveillance in polio eradication and identification of emerging viral encephalitis.

In 1988, when the World Health Assembly resolved to eradicate paralytic poliomyelitis, polio was endemic in 125 countries on 5 continents with an estimated 350,000 cases annually. By 2002, the number of countries was reduced to 7 and the number of cases by greater than 99%. Instrumental in this extraordinary progress is the timely detection and investigation of all cases of acute flaccid paralysis and the examination of stool samples in an accredited WHO Global Network laboratory. The Network consists of 124 National Poliovirus Laboratories, 15 Regional Reference Laboratories, and 7 Global Specialized Laboratories. Network Laboratories are held accountable to rigid performance standards for quality and timeliness in testing more than 60,000 stool samples annually. The Network is a hierarchical system in which polioviruses are isolated and identified in National Laboratories, differentiated as to wild or vaccine origin in Regional Reference Laboratories, and sequenced in Specialized Laboratories. Findings are promptly relayed to Regional and national program managers for immunization strategic planning, monitoring surveillance quality, and assessing eradication progress. Lessons from the Polio Laboratory Network demonstrate the value of a central coordinating body, an effective communication infrastructure, and full partnerships with peer epidemiology and medical sectors. Post-eradication polio surveillance will continue for many years. The Network legacy for other public health initiatives is access to an existing laboratory infrastructure and human resources with the proven ability to achieve technology transfer and quality laboratory performance even in resource-poor countries.

Stopping poliovirus vaccination after eradication: issues and challenges.

Since 1988 reported polio cases worldwide have declined by about 85% and the number of known or suspected polioendemic countries has decreased from over 120 to less than 50. With eradication of poliomyelitis approaching, issues potentially affecting when and how vaccination against poliovirus can be stopped become extremely important. Because of the potential risks and benefits inherent in such a decision, the best available science, a risk-benefit analysis, contingency plans, a stock pile of poliovirus vaccines, and the endorsement by the global policy-making committees will all be needed before vaccination can be discontinued. The scientific basis for stopping polio immunization has been reviewed by WHO. This Round Table article summarizes the current state of knowledge, provides an update on the processes and timelines for certification, containment, and stopping vaccination, and highlights some of the unanswered scientific questions that will be addressed by further research. These include whether transmission of vaccine-derived poliovirus strains could be sustained so that poliomyelitis could re-emerge in a future unvaccinated population and whether prolonged excretion of vaccine-derived poliovirus from individuals with immune deficiencies could be a mechanism through which this could occur.

Influenza A virus recycling revisited.

Current textbooks link influenza pandemics to influenza A virus subtypes H2 (1889-91), H3 (1990), H1 (1918-20), H2 (1957-58) and H3 (1968), a pattern suggesting subtype recycling in humans. Since H1 reappeared in 1977, whatever its origin, some workers feel that H2 is the next pandemic candidate. This report reviews the publications on which the concept of influenza A virus subtype recycling is based and concludes that the data are inconsistent with the purported sequence of events. The three influenza pandemics prior to 1957-58 were linked with subtypes through retrospective studies of sera from the elderly, or through seroarchaeology. The pandemic seroarchaeological model for subtype H1 has been validated by the recent recovery of swine virus RNA fragments from persons who died from influenza in 1918. Application of the model to pre-existing H3 antibody among the elderly links the H3 subtype to the pandemic of 1889-91, not that of 1900 as popularly quoted. Application of the model to pre-existing H2 antibody among the elderly fails to confirm that this subtype caused a pandemic in the late 1800's, a finding which is consistent with age-related excess mortality patterns during the pandemics of 1957 (H2) and 1968 (H3). H2 variants should be included in pandemic planning for a number of reasons, but not because of evidence of recycling. It is not known when the next pandemic will occur or which of the 15 (or more) haemagglutinin subtypes will be involved. Effective global surveillance remains the key to influenza preparedness.

Poliomyelitis eradication.

Since the poliomyelitis eradication program began in 1988, the number of poliovirus infected continents and countries have decreased from five to two and from greater than 100 to 53, respectively. A nearly 90% reduction in the incidence of polio has been achieved with a corresponding decrease in virus genomic heterogeneity. Major challenges to eradication remain in south Asia and Africa in those areas with hot and humid climates, high population density, and high birth rates. Of particular concern are countries with ongoing social unrest and poor health infrastructure. With the approaching eradication of polio, post-eradication issues are now being addressed. The World Health Organization (WHO) draft plan for containment of wild polioviruses has been published for comment. Commissions and committees for certification of eradication have been established. Still under discussion is the question of the appropriate strategy for stopping oral polio vaccine (OPV) immunization. Studies are underway to determine whether vaccine-derived polioviruses will continue to circulate after OPV cessation and the potential disease consequences of that circulation.

The principles of disease elimination and eradication.

The Dahlem Workshop discussed the hierarchy of possible public health interventions in dealing with infectious diseases, which were defined as control, elimination of disease, elimination of infections, eradication, and extinction. The indicators of eradicability were the availability of effective interventions and practical diagnostic tools and the essential need for humans in the life-cycle of the agent. Since health resources are limited, decisions have to be made as to whether their use for an elimination or eradication programme is preferable to their use elsewhere. The costs and benefits of global eradication programmes concern direct effects on morbidity and mortality and consequent effects on the health care system. The success of any disease eradication initiative depends strongly on the level of societal and political commitment, with a key role for the World Health Assembly. Eradication and ongoing programmes constitute potentially complementary approaches to public health. Elimination and eradication are the ultimate goals of public health, evolving naturally from disease control. The basic question is whether these goals are to be achieved in the present or some future generation.

Pandemic influenza: confronting a re-emergent threat. The 1976 experience.

The Swine Influenza Immunization Program began in January 1976 with an outbreak of swine influenza among trainees at Ft. Dix, New Jersey. The program ended in December 1976 after an increased incidence of Guillain-Barre syndrome was attributed to the vaccine. The issues and events of 1976 provide valuable lessons for the future. A thorough and objective review of the swine flu program should be a prerequisite for influenza pandemic planning. Strong consideration should be given to creating separate structures for risk assessment and risk management. Risk assessment estimates the probability of a pandemic, the options available for control, and the relative benefits of those options as situations change. Risk management is the political response to that assessment.

Poliovirus surveillance: building the global Polio Laboratory Network.

A network of virologic laboratories has been established by the World Health Organization to conduct surveillance for wild poliovirus and to provide evidence for the certification of poliomyelitis eradication. The network consists of >60 national laboratories isolating and identifying polioviruses within countries; 16 regional reference laboratories, providing intratypic differentiation of wild and vaccine strains and assisting with quality assurance and training; and 6 global specialized laboratories, conducting research, preparing reference reagents, and providing genomic sequencing of wild polioviruses, advanced training, and expert virologic advice. Laboratories collaborate with national eradication programs in the detection, reporting, clinical investigation, and virologic testing of stool specimens obtained in connection with cases of acute flaccid paralysis and, where indicated, from healthy children and the environment. A quality assurance system, leading to World Health Organization accreditation, involves training in standardized techniques, use of centrally prepared typing antisera, annual proficiency testing and follow-up action, and monitoring of standard performance indicators.

The biologic principles of poliovirus eradication.

The biologic principles for the global eradication of poliomyelitis are as follows: Poliovirus causes acute, nonpersistent infections, virus is transmitted by infectious humans or their waste, survival of virus in the environment is finite, humans are the only reservoir, and immunization with polio vaccine interrupts virus transmission. These principles appear to be sound. The potential for prolonged virus excretion by immunocompromised patients requires further definition, although there is no epidemiologic evidence of a threat to eradication. Survival of poliovirus in the environment is highly variable, but viral inactivation is usually complete within months. Higher primates may be infected with poliovirus, but they are unlikely reservoirs in nature. The only poliovirus reservoir remaining after eradication will be laboratory stocks. Serious attention must be given to reducing this potential source of infection. Polio eradication through immunization is evidenced by the documented absence of poliomyelitis in an increasing number of countries and the progressive disappearance of poliovirus genotypes.

Quest for life-long protection by vaccination.

Life-long protection from disease through immunization can be accomplished through individual or community protection. Individual protection is the goal for vaccination against diseases that have inanimate or animal reservoirs or that pose risks for certain populations. Community protection is the goal for vaccination against diseases that are transmitted only from human to human. Community protection afforded by childhood vaccines has been highly successful against measles, rubella, mumps, and polio. However, outbreaks of measles, rubella, and mumps continue to occur, primarily because of inadequate immunization of children under age 2. Simplification of vaccination regimens, provision of incentives to care providers and parents, and increased access to care should improve vaccination rates in the United States. Better protection requires better use of available vaccines. Eradication of disease through vaccination is the ultimate goal of community protection. Elimination of the infectious agent is the most effective means of achieving life-long protection. The World Health Organization's (WHO) smallpox eradication campaign eliminated a serious disease as well as the need for a vaccine with frequent and severe adverse reactions. The discontinuation of smallpox vaccination in the United States has produced a savings of over $3 billion. Polio has been targeted by WHO for eradication by the year 2000. The eradication of polio and the elimination of the need for polio vaccination in the United States should result in a savings of $110 million per year in vaccine costs alone. Strong United States support is crucial for WHO to reach its goal. Any of the vaccine-preventable childhood virus diseases could be eradicated with sufficient national and international will. Measles and hepatitis B should be high priorities. The ultimate goal of vaccination is life-long protection of all individuals. Any disease of sufficient public health importance to warrant routine vaccination is of sufficient importance to warrant eradication wherever judged to be possible.

The epidemiology of AIDS: current status and future prospects.

The reported incidence of acquired immune deficiency syndrome (AIDS) continues to increase in countries throughout the world. On the basis of a polynomial model for extrapolation, the cumulative number of cases diagnosed and reported since 1981 in the United States is expected to double during the next year with over 12,000 additional cases projected to be diagnosed by July 1986. The annual incidence rates for single (never-married) men in Manhattan and San Francisco, intravenous drug users in New York City and New Jersey, and persons with hemophilia A ranged from 261 to 350 per 100,000 population during 1984. For single men aged 25 to 44 years in Manhattan and San Francisco, AIDS was the leading cause of premature mortality in 1984 as measured by years of potential life lost. Infection with HTLV-III/LAV is considerably more common than reported AIDS in high-risk populations and can persist at least for several years, so the presence of specific antibody should be considered presumptive evidence of current infection. The screening of donated blood and plasma for antibody to HTLV-III/LAV and use of safer clotting factor concentrates should greatly reduce HTLV-III/LAV transmission through blood and blood products. Most HTLV-III/LAV infections occur through sexual transmission, use of contaminated needles, and as a result of infected mothers passing the virus to newborns. Continued research commitment is needed to develop an HTLV-III/LAV vaccine and therapy for this infection. In the interim, widespread community efforts are needed to minimize transmission.

Surveillance and control of infectious diseases: progress toward the 1990 objectives.

Great progress has been made in the United States in reducing infectious disease mortality. However, infectious diseases remain the greatest cause of morbidity in this country. Newer infectious diseases or agents have been recognized, but newer tools for surveillance and control have also been made available. Specific objectives for the reduction of infectious diseases by 1990 have been set by the Public Health Service. The opportunities appear to be good for achieving by 1990 objectives for nosocomial infections, Legionnaires' disease, tuberculosis, and surveillance and control of infectious diseases. Achievement of the 1990 objectives for hepatitis B, pneumococcal pneumonia, and bacterial meningitis, however, will require both scientific advances and additional resources.