increased with successive booster injections. The study reported that three people had brief and mild fever.

Brachman Study

Brachman and colleagues (1962) conducted the only randomized clinical trial of vaccination with a protective antigen anthrax vaccine. Although the vaccine used in this study was similar to the current vaccine (used to immunize Gulf War troops and currently available in the United States) in that it was a PA vaccine, the manufacturing process has since changed and a different strain of anthrax bacillus is now used (GAO, 1999c).

The clinical trial was conducted among 1,249 eligible workers6 at four goat hair processing mills in which some raw materials were contaminated by anthrax bacilli. Both cutaneous and airborne anthrax were endemic; approximately one case of anthrax occurred per 100 employees per year in these mills. After the initial series of three injections, the study had to be terminated at the largest mill, which employed nearly half of the subjects, because of an outbreak of inhalation anthrax that required the vaccination of all employees. At the remaining mills, 480 participants completed the series of injections (230 of whom were randomized to receive active vaccinations and 250 to receive placebo injections) and 81 participants did not complete the series.7 The study subjects did not know whether they had received the active vaccine or placebo; the article does not state whether the investigators were also blinded to the allocation.

The report of the study does not always clearly state whether the results in the three mills apply only to the 480 subjects who completed the vaccination series or also included results from the 81 subjects who did not complete the series. Neither does it state whether the results apply only to the 480 subjects in the three mills who completed the series or whether the results include the subjects from the largest mill who had been randomized, received the initial injections, and were partially evaluated prior to the decision to withdraw the mill’s employees from the study.

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 (there was further monitoring for the vaccine’s efficacy).

Of the 230 actively vaccinated subjects who completed the inoculations, one individual (0.4 percent) developed anthrax. Of the 250 individuals receiving placebo, 12 (4.8 percent) developed anthrax. The great majority of cases of an-


Employees who had a previous case of anthrax were not eligible for the study. Of the 1,249 employees eligible for participation, 340 refused to participate in the study.


The authors state that there was a gradual decline in participation in the study, partly because of changes in the nature of the textile business and partly because some of the employees withdrew from the program. Reasons for withdrawal were not stated.

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