Vaccinating an entire population against anthrax before there is an immediate threat of a biological warfare attack is not cost-effective, results of statistical analysis suggest.

If an attack does occur, mass vaccinations plus administration of antibiotics would be the best strategy, Dr. Robert A. Fowler at the University of Toronto in Canada and colleagues explain in their report in the Annals of Internal Medicine.

The authors compared the costs, harms and benefits of offering vaccination or antibiotics to a hypothetical cohort of people in a large metropolitan city.

They assumed that the yearly probability of an attack is 1 percent, that 10 percent of the population would have sufficient exposure to anthrax spores to cause clinical disease, and that 95 percent of these would develop severe inhalational anthrax unless given antibiotics or a vaccine.

A combination strategy of three vaccinations administered 2 weeks apart and antibiotics after an attack would prevent more cases of Anthrax and more deaths than either approach alone, the team calculated. It would also save $355 per person compared with vaccination alone.

No preventative measures at all would be the most expensive strategy, the investigators note, because of the high cost of treating inhalational anthrax.

“These findings highlight the critical need for distribution systems that can rapidly provide prophylaxis and vaccination for hundreds of thousands, perhaps millions, of exposed people,” Fowler and colleagues conclude.

Dr. Glenn F. Webb, at Vanderbilt University in Nashville, Tennessee, says in an accompanying editorial that the researchers did an excellent job analyzing the policy issues of an attack, but “they may underestimate the incalculable societal impact of such an attack,” which might result in social panic and chaos.

Webb says measures such as implementation of technology to detect the release of anthrax spores, stockpiling of emergency supplies, and scientific research into the development of vaccines, antibiotics, and antidotes “are imperative.”

SOURCE: Annals of Internal Medicine, April 19, 2005.