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Anthrax booster expanded to 3 years for moderate-risk groups



A booster dose for pre-exposure prophylaxis with an anthrax vaccine may be given at 3 years after an initial series for individuals not currently at risk who wish to maintain protection, according to the Centers for Disease Control and Prevention’s Advisory Committee on Immunization Practices.

Carolina K. Smith, MD/

In a unanimous 15-0 vote at the February meeting, ACIP committee members agreed on the recommendation after adjusting the wording to reflect a permissive, rather than mandated, guidance.

William Bower, MD, of the CDC’s National Center for Emerging and Zoonotic Infectious Diseases (NCEZID), presented data on Anthrax Vaccine Adsorbed (AVA) to support its protective effects over a longer booster dose interval.

The recommendations apply to persons aged 18 years or older who are not currently at high risk of exposure to Bacillus anthracis, but who might need to deploy to a high-risk area quickly, such as military personnel, Dr. Bower said.

In addition, data suggest that adults who have started, but not completed the pre-exposure priming series, can transition to the postexposure schedule prior to entering a high-risk area, he noted.

The previous pre-exposure anthrax vaccination schedule was a three-dose priming series at 0, 1, and 3 months, followed by a booster at 12 months and 18 months, then annually.

Data from several human immunogenicity studies showed a robust immune response following a delayed anthrax booster dose, with “sustained immunological memory to at least month 42,” and suggested that even longer intervals between boosters may be possible, Dr. Bower said.

A dosing schedule of intramuscular injections at 0 and at 1 month and 6 months, with a booster at 42 months yielded survival estimates of approximately 84%-93%.

Dr. Bower noted that a new vaccine, AV7909, has demonstrated safety and effectiveness similar to AVA and could be used for pre-exposure prophylaxis if AVA is not available. AVA remains the preferred option, but ultimately will be replaced by AV7909, when the current AVA stockpile is exhausted.

Additional safety data on AV7909 will be reviewed by ACIP as they become available, and future guidance from the CDC will include statements on dosing for special populations including pregnant and breastfeeding women, said Dr. Bower.

“We anticipate that this [anthrax vaccine] work group will reconvene in 2021 to review data from pending studies” of AV7909, he said.

The ACIP members had no financial conflicts to disclose.

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