Diluted smallpox vaccine still is effective

Smallpox is a highly contagious viral disease that killed untold millions until it was officially eradicated in 1979. But fears after the September 2001 attacks that it might be used as a biological weapon sparked a U.S. effort to ensure there was enough vaccine. Now researchers have reported that heavily diluted doses of the existing vaccine remain effective, which means the U.S. stockpile of the vaccine can be stretched if needed.

Although vaccinations have not been recommended for the general public because of potentially lethal side effects in rare cases, tens of thousands of front-line military and healthcare workers have been vaccinated.

In the study, published in last week’s Journal of the American Medical Assn., volunteers ages 18 to 32 were given one of three strengths of smallpox vaccine. The weakest was diluted to one-tenth the original, and nearly all developed a telling pustule at the inoculation site within six to 11 days, indicating the dosage’s effectiveness.