Rapid response with antibiotics would be a more effective way of handling an anthrax terror attack than a preemptive mass vaccination program, scientists said on Wednesday.

They estimate that if people exposed to anthrax spores received antibiotics within six days, 70 percent of infections could be prevented. Delaying treatment 10 days or more however would cut the figure to less than 50 percent.

“Strengthening the public health infrastructure to improve early detection and rapid response is going to be a better use of resources to improve disease surveillance and to get drugs out to people quicker than a mass pre-attack vaccine program,” said Ron Brookmeyer, of the Johns Hopkins Bloomberg School of Public Health in Baltimore, Maryland.

He and his colleagues developed a probability model to predict how an anthrax outbreak could be contained with different antibiotic and vaccination strategies before and after an attack. Their research is reported in the science journal Nature.

They found that only a vaccine program aimed at immunizing the majority of people would significantly increase the prevention rate over and above what could be done with a rapid response after an attack. But getting those levels of vaccine coverage may not be feasible.

Brookmeyer told Reuters that having an improved anthrax vaccine on hand is still important because if people are exposed to high doses of spores, a vaccine given after an attack could reduce the course of antibiotics people would need to take.

Anthrax, a disease of wild animals and livestock, is considered a likely bioterror weapon because its microscopic spores are easy to produce and their release could cause widespread disease and panic.

Five people died in the United States in 2001 when anthrax spores were used in a series of letter attacks. Brookmeyer said some of the U.S. postal workers who were infected did not begin taking antibiotics until nine days after they were exposed.

The researchers concluded that widespread immunization with the current licensed anthrax vaccine is not practical because it must be given in six doses over 18 months to produce immunity.

California vaccine maker VaxGen Inc is working on a new, improved version of the vaccine that should be available within three years.

At least 64 percent of the population would have to be immunized before an attack to reach a prevention rate of 90 percent, according to the scientists.

They estimated that if a vaccine were 95 percent effective and given after exposure it could cut the time antibiotics would be needed. It would also prevent cases if an antibiotic resistant strain of anthrax were used.

“Shortening the duration of time before we get drugs to people and detecting outbreaks quicker would be a more effective use of our resources,” Brookmeyer added.

Anthrax can be transmitted through inhalation of the spores, through a cut in the skin, or by eating contaminated beef. Inhaled anthrax is the deadliest form because by the time symptoms appear it is often too late for treatment.

SOURCE: Nature, December 16, 2004.