Medical Readiness:

Issues Concerning the Anthrax Vaccine

T-NSIAD-99-226: Published: Jul 21, 1999. Publicly Released: Jul 21, 1999.

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Kwai-Cheung Chan
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Pursuant to a congressional request, GAO discussed the results of its work on the anthrax vaccine, focusing on: (1) the extent to which data support the need for six initial shots and an annual booster of the anthrax vaccine; (2) the relative merits and weaknesses of a passive surveillance system in determining adverse events; (3) the available data on differences in adverse reaction rates between men and women receiving the anthrax vaccine; and (4) the disadvantages of the vaccine and the status of federal efforts to develop an improved anthrax vaccine.

GAO noted that: (1) no studies have been done to determine the optimum number of doses of the anthrax vaccine; (2) a study done during the early 1950s showed that animals could be protected against cutaneous anthrax using a three-dose schedule; (3) however, the number of doses was increased to six when three people who had received three doses of the vaccine were infected after exposure to anthrax; (4) in a study of the vaccine's human efficacy published in 1962, a six-dose schedule was used, and the researchers concluded that the vaccine provided protection against cutaneous exposure to anthrax; (5) in 1998, the manufacturer of the vaccine submitted a Food and Drug Administration (FDA) application to determine whether the number of shots in the initial schedule could be reduced from six to five; (6) although annual boosters are given, the need for this frequency and the amount of the booster dose has also not been evaluated; (7) Department of Defense (DOD) submits data on adverse events associated with the anthrax vaccine to the Vaccine Adverse Events Reporting System; (8) this system has several advantages; (9) it alerts FDA and Centers for Disease Control and Prevention (CDC) to previously unreported or unexpected increases in reported adverse events; (10) it is also a relatively affordable way to supplement the data collected on vaccines before they are licensed; (11) however, it is a passive surveillance system, which means that FDA and CDC must rely on vaccine recipients or their health care providers to report any adverse events after receiving the vaccine; studies show that adverse events are reported significantly less than they would be in an active surveillance system; (12) DOD has conducted three efforts to actively collect data on adverse reactions after servicemembers received the anthrax vaccine; (13) data from these efforts show that women reported twice the rate of adverse reactions than men for both local and systemic reactions; (14) a higher proportion of women than men reported making an outpatient medical visit after a vaccination, and more than twice the percentage of women reported that they missed one or more duty shifts after their vaccinations than did men; (15) the anthrax vaccine has several disadvantages; (16) the amount of protective antigen in the vaccine cannot be precisely measured, and it varies from lot to lot; and (17) also, the requirement for a six-dose schedule and annual booster shots, rather than a smaller number of doses, complicates the logistics of inoculating all of DOD's troops and increases the cost of the vaccine program.

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