BioEd Online

Mass vaccination is not the best way to deal with the threat of anthrax attacks by terrorists, say researchers who have evaluated the outcomes of various strategies. Far better, they say, is to ensure that the right treatments will be delivered to those exposed as soon after the attack as possible.

Chief among those treatments should be antibiotics, say Ron Brookmeyer, of the Johns Hopkins Bloomberg School of Public Health in Baltimore, Maryland, and his colleagues. Supplying them to everyone exposed within six days of the outbreak's detection would cut disease cases by around 70%, they calculate. But after ten days or more (the wait endured by many exposed to the US postal anthrax attacks in late 2001), cases are decreased by less than 50%.

Pre-emptive mass vaccination is unlikely to improve these numbers unless the coverage is very extensive, the researchers add. The existing vaccine, though effective, requires months of injections, and distributing it to the general public is likely to be very costly.

But this doesn't mean that there is no role for a new, improved vaccine, the researchers add. Delivering a vaccine to those already exposed could reduce the length of antibiotic treatment required or help to fend off an antibiotic-resistant strain of the pathogen.

Resource and reward

"In terms of resources, the priority should be rapidly detecting an attack when it occurs," Brookmeyer told news@nature.com. "Then you need a plan to get antibiotics to people quickly."

That would minimize disease by maximizing the chances that anthrax spores in the body are killed off before they can germinate in the lymph nodes and cause sickness.

Brookmeyer's team drew their conclusions using a computer model that takes account of the amount of spores inhaled, chances of germination and the rate of spread. The analysis, reported in this week's Nature¹, also takes account of whether people are vaccinated, how quickly they get their antibiotics, and whether they stick to them for the full course of treatment.

"In the 2001 attacks, less than 50% of people completed their 60-day antibiotic course," Brookmeyer points out. There were 19 disease cases and 5 fatalities in total, and although nobody got sick after stopping their antibiotics early, this behaviour could easily have led to more disease, he says.

"I don't think we've learned all the lessons from 2001," Brookmeyer adds. In July this year, President George W. Bush signed legislation to empower Project BioShield, which will provide funding for research against anthrax. But public-health surveillance to detect anthrax attacks still needs to be improved, Brookmeyer warns.

In another analysis published last year², Edward Kaplan, an epidemiologist at the Yale School of Management in New Haven, Connecticut, and his colleagues suggested that the most effective pre-attack measures should include training and vaccination of all healthcare workers who would have to deal with an outbreak.

They also suggested pre-emptively supplying antibiotics such as ciproflaxin, to be taken if needed by those exposed. It would be difficult, however, to ensure that those given the drugs could be relied on to use them correctly.

Vaccine research should still continue, Brookmeyer advises, because of the benefits in supplying it to those exposed, rather than simply blanketing the population. "An improved vaccine will be important," he says. "But we need to bring good and thoughtful science into biosecurity. We need to do these kinds of calculations to decide where we will get the biggest bang for your buck."