Smallpox vaccination program 2003

The terrorist attacks on the World Trade Center and the Pentagon on 9/11, and the anthrax attacks that followed shortly thereafter, served to focus attention on the threat of bioterror. Smallpox, for reasons delineated above, is widely considered to be a high priority threat agent, and one for which an effective vaccine exists, although not in sufficient quantity for broad application. In late 2002 the Federal Government authorized the implementation of a smallpox vaccination program for over half-a-million operational military personnel, and a second program, presided over by the states, to vaccinate civilian "smallpox response teams" comprising health-care workers and other emergency response personnel (Faden et al., 2003).

Routine use of smallpox vaccine ceased in 1972, at which point it was determined that the potential risk of vaccine-associated adverse events significantly outweighed the risk of smallpox (Fenner et al., 1988). Because smallpox vaccine may be associated with a number of potentially life-threatening toxicities, and at the time the programs were implemented there was no clearly definable risk of a smallpox exposure, the decision to proceed with pre-event vaccinations provoked a vocal national debate, raising a number of statistical, scientific, political, legal, and ethical issues that informed public health response planning in general.

Many of the issues were controversial and complex: whether vaccination of health-care workers is preferable to mass vaccination of the public (Kaplan et al., 2002; Bozzette et al., 2003); and the risk-to-benefit ratio for health-care workers, and how to compensate them in the event of vaccine-related injury (Faden et al., 2003). While these and other issues sparked useful discussion, the most significant development related to the smallpox vaccination program was probably the recognition of hitherto unrecognized toxicity information concerning the vaccine itself.

Smallpox vaccine has a well-described toxicity profile that includes such serious but predictable complications as post-vaccinial encephalitis, a rare, potentially fatal neurologic syndrome generally seen in young children; progressive vaccinia, frequently fatal and seen in immunocompromised hosts; generalized vaccinia; eczema vaccinatum, dissemination of the vaccine virus seen in hosts with eczema or atopic disease; and contact transmission of vaccinia to an unvaccinated host (Artenstein, 2004b). Historically, 1 per million vaccinees developed a fatal complication (Lane et al.., 1970). The vaccination program was designed to screen participants carefully in order to minimize the potential for serious sequelae (CDC, 2003); in general it was successful in this regard, with over 730,000 military personnel and 40,000 civilian volunteers vaccinated, and very low rates of predictable, serious adverse events noted (Grabenstein and Winkenwerder, 2003; Poland et al, 2005).

Because of the questions concerning risk outweighing benefit in the pre-event setting, the vaccine program was subjected to more rigorous scrutiny than historical smallpox mass vaccination. As may be seen with such large, well-studied datasets, novel and unanticipated effects were observed. Ischemic cardiac events occurred in 24 military and 9 civilian vaccinees; in retrospect, most had underlying coronary artery disease, and the incidence of ischemia did not exceed the level expected in an age-matched, unvaccinated population (Poland et al., 2005). On the other hand, 86 cases of myopericarditis in military vaccinees and 22 cases among civilians were recognized, leading an expert panel to conclude that smallpox vaccination is casually related to myopericarditis and increases the risk of this complication (Poland et al., 2005). Thus, data gleaned from preparations for a potential bioterrorist attack using smallpox will inform future vaccine efforts for smallpox (Artenstein et al., 2005) as well as other areas of biodefense.

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