public, the health-care providers, and the public-health community. Such acceptance is enhanced the closer the vaccine comes to meeting the ideal set of characteristics previously mentioned. Much discussion about vaccines is devoted to assuring efficacy, but safety is equally as important. Widespread acceptance of vaccines can only be assured if the public believes vaccines will not harm them. Concerns about vaccine safety led to marked drops in pertussis vaccine coverage in Japan and the United Kingdom in the 1970s, with resultant major epidemics of whooping cough (2, 3). The quest for life-long protection needs to be accompanied by a quest for completely safe products.

Even though no vaccine today is perfectly safe or perfectly effective, with the right strategy less-than-perfect vaccines can be powerful prevention tools. Diseases can be eradicated with a strategy for vaccine use tailored to both the characteristics of the vaccine and the epidemiology of the disease.

PROTECTION THROUGH VACCINATION

Life-long protection from disease through vaccination can be accomplished in two ways: (i) individual protection—assuring a life-long immune response capable of repelling challenges individuals may receive at any time in their lives, and (ii) community protection—reducing or even eliminating the possibility that nonimmune individuals will be exposed to the infectious agent.

All vaccines are given to protect individuals. Individual protection is the only way to assure life-long protection against certain diseases with inanimate or animal reservoirs for infectious agents, such as tetanus and rabies (4, 5). For these diseases, vaccinated humans do not help to protect unvaccinated humans. All susceptible persons are at risk, and that risk is not modified by reducing the number of susceptibles through vaccination. Individual protection is also the only protection available when vaccines are recommended for selected populations whose behaviors place them at increased risk of disease exposure. These are vaccines needed for international travel, special life-styles, selected occupations, and other special uses. Included among these are Japanese encephalitis (6), yellow fever (7), typhoid (8), adenoviruses 4 and 7 (9), anthrax (9), cholera (10), rabies (11), and meningococcal (12) vaccines.

While influenza and pneumococcal vaccines are recommended for all adults ≥65 years of age and selected others with high-risk medical conditions, these vaccines do not substantially reduce population exposure to the organism (13, 14).

For each of these diseases, temporary or life-long protection can only be obtained through vaccination of each individual at risk. The ability to



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