nonendemic areas was principally to close family members, even when a high proportion of the population had not been vaccinated [13, 14]. Although the human-to-human transmission rate of the disease can be high, an individual infected patient did not have numerous close contacts unless he or she was in a large household, a hospital, or some other institution (homes for elderly, for example, suffered in recorded outbreaks). This experience suggests that a future outbreak of smallpox would infect people of all ages, but that the epidemic would not become explosive, as would be the case with a disease transmitted prior to the onset of illness.

Control Strategies

Herd immunity (a large number of immune individuals in the exposed population) limits the spread of diseases transmitted by subclinically infected persons or patients who are fully mobile. It is less important for smallpox, since once infectious, patients are typically confined to bed. Hindsight reveals that the vast majority of vaccinations during the panics associated with smallpox outbreaks in the past were unnecessary since transmission was limited mainly to close contacts within the household or hospital. Prompt diagnosis, isolation, and vaccination of close contacts is of much greater importance. This was essentially the strategy employed in the global eradication program.

Given that the disease would probably be transmitted to the second generation of patients before being diagnosed, however, suitable antiviral therapies would be of great value. Yet, as discussed in Chapter 6, no currently available antiviral agent is effective against variola virus infection, development of such an agent would be time-consuming and costly, and its therapeutic effectiveness would remain unproven until an outbreak occurred.

A smallpox outbreak would be a medical emergency. Criteria for contraindications to vaccination and for the type of vaccine to be used would need to be less strict than in the absence of the disease. Rapidity of response would probably be of greater immediate concern than safety. Nevertheless, the considerable number of individuals immunocompromised as a result of the AIDS epidemic and increased organ transplant and chemotherapy procedures constitute a special risk since inoculating these individuals with the traditional live vaccinia vaccine is not acceptable (see also Chapter 7).

The lessons of the past can help us prepare for future smallpox outbreaks. At the same time, however, the techniques of the past need to be augmented by the best contemporary knowledge available.



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