The primary use of the anthrax vaccine in humans was initially for the protection of occupationally exposed individuals (e.g., persons working with animal hair or hide, including goat hair mill workers, tannery workers, and veterinarians). Protective antigen, one of the three toxin proteins produced by the anthrax bacillus, is the immunogenic component of both the U.S. and the U.K. vaccines. The U.S. vaccine is an aluminum hydroxide-adsorbed cell-free culture filtrate of an unencapsulated anthrax strain (Pile et al., 1998). Product licensure for Anthrax Vaccine Adsorbed was granted on November 10, 1970. It is estimated that 68,000 doses of the U.S. anthrax vaccine were distributed from 1974 to 1989, 268,000 doses in 1990, and 1.2 million doses from 1991 to July 1999 (Ellenberg, 1999). The exact number of people who received the vaccine is not known. The current dosing schedule is 0.5 ml administered subcutaneously at 0, 2, and 4 weeks and 6, 12, and 18 months, followed by yearly boosters.
In December 1997, the Secretary of Defense announced that all U.S. military forces would receive anthrax vaccinations for protection against the threat of biological warfare. The Anthrax Vaccine Immunization Program began vaccinations in March 1998.
There is a paucity of published peer-reviewed literature on the safety of the anthrax vaccine. Brachman and colleagues (1962) conducted the only randomized clinical trial of vaccination with a protective antigen anthrax vaccine.6 The clinical trial was conducted among eligible workers at four goat hair processing mills in which some raw materials were contaminated by anthrax bacilli. Participants were examined 24 and 48 hours following each vaccination to assess both local and systemic reactions to the vaccine. There were no reports of subsequent active or passive surveillance for possible adverse effects beyond 48 hours after each vaccination (however, there was further monitoring for the vaccine’s efficacy). The typical reaction is described as a ring of erythema (1–2 cm in diameter) at the injection site, with local tenderness that lasted 24–48 hours. Some subjects (a number was not given) reported more extensive edema, erythema (more than 5 cm in diameter), pruritus, induration, or small painless nodules at the injection site (lasting up to several weeks). Twenty-one individuals had moderate local edema that lasted up to 48 hours. The only systemic reactions were reported in two individuals (0.9 percent of the actively vaccinated subjects) who experienced “malaise” lasting 24 hours following vaccination. The study notes that three individuals who received the placebo (0.1 percent