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The newspaper of The Johns Hopkins University December 20, 2004 | Vol. 34 No. 16
Study Models Impact of Anthrax Vaccine

By Tim Parsons
Bloomberg School of Public Health

Rapidly distributing antibiotics to people exposed to anthrax spores during a bioterrorist attack could, by itself, prevent about 70 percent of anthrax infections, 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 policy-makers who must develop effective strategies for containing an anthrax outbreak. The study is published in the Dec. 16 edition of Nature.

The Johns 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 six 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 nine 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 that could begin to provide immunity ranging between seven 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 by up to 43 days.

An 80 percent effective vaccine could reduce time on antibiotics by up to 23 days. The vaccine also could prevent cases if an antibiotic-resistant strain of anthrax were used in an attack.

"Our study highlights the need for rapid distribution of antibiotics to minimize casualties from an anthrax outbreak," said Ron Brookmeyer, lead author of the study and professor in the Department of Biostatistics. "But a long course of antibiotics is not ideal, and a new, improved anthrax vaccine could be especially helpful in reducing duration of antibiotic treatments."

The study was written by Ron Brookmeyer and Elizabeth Johnson, in Biostatistics at the Bloomberg School, and Robert Bollinger, in the Division of Infectious Diseases at the School of Medicine. The research was funded by the Fogarty International Center and the National Institute of Allergy and Infectious Diseases.


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