Mass vaccination may not be necessary to contain smallpox in the event of a biowarfare attack, scientists said on Wednesday.

Instead, they suggested that spotting an outbreak early and vaccinating affected individuals and front-line workers will be enough to ensure safety.

“Our results suggest that outbreaks can be contained by a strategy of targeted vaccination combined with early detection without resorting to mass vaccination of a population,” Dr Stephen Eubank, of the Los Alamos National Laboratory in New Mexico, said in a report in the science journal Nature.

Smallpox is a serious and sometimes fatal infectious disease that was eradicated decades ago after a successful worldwide vaccination program.

Small stocks of the virus have been kept in laboratories in the United States and Russia. After the September 11 attacks on New York and Washington and deaths from anthrax-tainted letters in the United States, there have been fears that other nations could develop smallpox as a biological weapon.

Britain has admitted that it was preparing for a mass smallpox vaccination of its population in the event of a bioterror attack.

Several vaccine companies, including Britain’s Acambis and Bavarian Nordic of Denmark have secured lucrative government contracts for the supply of stockpiles of smallpox vaccine.

But Eubank and his team believe it may not be needed. Using models of a smallpox outbreak in a city similar to Portland, Oregon, they tested several strategies to restrict the spread of the disease.

They concluded that the time it takes for people to get home is by far the most important factor, followed by any delay in response to an outbreak.

“This indicates that targeted vaccination is feasible when combined with fast detection,” Eubank added.

Smallpox has an incubation period of around 12 days. Symptoms include chills, fatigue and fever followed by pustules that erupt mainly on the face and limbs.

SOURCE: Nature, May 13, 2004.