Several countries are believed to have biological weapons programs capable of causing widespread devastating illness among unprotected individuals. Bacillus anthracis, the causative agent of anthrax, is one of the most likely pathogens used. The decision by Secretary of Defense William S. Cohen to vaccinate the U.S. Armed Forces against anthrax, using a licensed vaccine with which most civilian and military medical personnel were unfamiliar, prompted this review of the evidence of the safety and efficacy of the vaccine (anthrax vaccine adsorbed, AVA). Data collected on the safety of AVA by active monitoring after vaccination indicated that mild local reactions, consisting of 1-to 2-cm erythema plus slight local tenderness, occurred in approximately 30 percent of recipients. Moderate local inflammatory reactions occurred in 4 percent of recipients of the second injection. More severe local reactions occurred less frequently and consisted of extensive edema of the forearm in addition to the local inflammatory reaction. Systematic reactions occurred in less than 0.2 percent of recipients and were characterized by malaise and lassitude, and less frequently by fever and chills. Evidence for the efficacy of the licensed AVA is based on data from both humans and animal models. Efficacy was evaluated in a placebo-controlled, single blind study carried out in goat hair mill workers in four New Hampshire mills from 1955 to 1959, at risk for cutaneous anthrax. Cutaneous anthrax continued to occur, but several months after the study began, there was an outbreak of inhalational anthrax. Vaccination resulted in a statistically significant reduction in the incidence of anthrax in the vaccinated compared with the placebo group. In nonhuman primates, the model that best approximates inhalational anthrax in humans, AVA provided close to 100 percent protection against an aerosol challenge with the Ames strain. The risks associated with anthrax immunization must be weighed against the risk of no intervention, namely, the possibility of large numbers of fatalities after biological attack. The potential benefit to members of the armed forces is the prevention of death from a well-recognized, lethal battlefield or terrorist threat versus the known risk of transient, predominantly local adverse effects. The Department of Defense Anthrax Vaccine Immunization Program is in place to protect military personnel from a significant biological threat. This policy is based on the assessment of the threat, the almost uniformly fatal nature of inhalational anthrax in unprotected individuals, and the availability of an FDA licensed vaccine. References