Anthrax Vaccine Approved for Postexposure Protection

November 24, 2015

The US Food and Drug Administration (FDA) has repurposed a 45-year-old vaccine against anthrax for postexposure protection.

Anthrax vaccine adsorbed (BioThrax, Emergency BioDefense Operations) was approved in 1970 to prevent the disease in individuals at high risk for exposure. The FDA announced Monday that it was adding a new indication to prevent anthrax after suspected or confirmed exposure to Bacillus anthracis, the disease-causing bacterium, in individuals from 18 to 65 years of age. Clinicians should order the vaccine in conjunction with recommended antibiotic treatment.

If not treated promptly, anthrax is often fatal, especially when a person develops the inhalation form of the disease after breathing in anthrax spores.

"Anthrax is considered one of the more likely agents to be used in a biological attack, primarily because its spores are very stable and easy to disperse," the FDA said in a news release. The agency noted that people on rare occasions may contract the disease through contact with infected animals or contaminated food.

The agency based the decision in part on studies of rabbits that were exposed to B anthracis. Those treated with the vaccine together with antibiotics had a survival rate between 70% and 100%, depending on the vaccine dose. Survival rates slipped to 44% and 23%, respectively, in two other studies in which exposed rabbits received only antibiotics.

Another study conducted by the federal government looked at the antibody response to BioThrax in humans, along with the vaccine's safety. Two hundred healthy adults received subcutaneous injections in three doses over the course of 4 weeks. In most study participants, the antibody response correlated to a 70% probability of survival seen in the rabbit study.

Adverse reactions in the human study resembled those observed when the vaccine is used for preexposure protection against anthrax. Tenderness, pain, swelling, redness at the injection site, and limited arm movement made up the majority of localized adverse reactions. The most common systemic ones were muscle ache, headache, and fatigue.

More information on today's FDA decision is available at the agency's website.


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