Rapidly distributing antibiotics to people exposed to anthrax spores during a bioterrorist attack, could by itself, prevent about 70 percent of anthrax infections from occurring, according to researchers from the Johns Hopkins Bloomberg School of Public Health.
To increase the prevention rate to 90 percent, their study found that at least 63 percent of the population would need to be immunized with vaccine before an anthrax attack, which might not be practical. However, the study found that anthrax vaccination given even after an attack could be beneficial in reducing the length of time antibiotic treatment would be needed. These findings could be an important tool for policymakers who must develop effective strategies for containing an anthrax outbreak. The study is published in the December 16, 2004, edition of Nature.
The Hopkins researchers developed a probability model to predict how many cases of anthrax could be prevented under varying conditions. The study found that about 70 percent of anthrax cases could be prevented if antibiotics were distributed within 6 days after exposure and patients were to take them for 60 days. Prevention rates dropped below 50 percent if antibiotics were delayed more than 10 days. In 2001, some postal workers did not begin taking antibiotics until 9 days after exposure.
The current licensed anthrax vaccine requires six doses over an 18-month period to provide immunity. The researchers looked at what impact a new and improved anthrax vaccine could have, and evaluated a range of vaccine characteristics, which could begin to provide immunity ranging between 7 and 28 days. When vaccine was distributed along with antibiotics after an attack, the researchers calculated that vaccine prevented few additional cases from occurring when compared to just rapid use of antibiotics. However, they found that if the vaccine is 95 percent effective, it could reduce the time that antibiotics would be needed up to 43 days.