HHS intends to obtain more than 75 million additional doses of smallpox vaccine from Aventis Pasteur Inc., provided the decades-old vaccine supply is proven safe and effective, said HHS Secretary Tommy G. Thompson.

The additional supply could further boost the U.S. stockpile of smallpox vaccine, which has been a significant priority of HHS' bioterrorism preparedness plan. Existing U.S. vaccine stockpiles and contracts to produce new vaccine will result in at least 286 million doses of vaccine being available by the end of this year - enough to vaccinate the entire U.S. population in the unlikely event of a smallpox outbreak. If proven usable, the Aventis Pasteur stock would add to this supply and provide further protection, particularly in the short term.

"If we determine that the Aventis vaccine remains effective, we could substantially boost our nation's smallpox vaccine stockpile at relatively little cost to taxpayers," Secretary Thompson said. "The Aventis supply could provide an added safety net should we need to vaccinate against smallpox."

The agreement would involve an estimated 75 million to 90 million doses of vaccine produced by Aventis that has been stored in a secure location since 1972, when the U.S. ended routine vaccinations for smallpox.

HHS agencies have been working with Aventis on preliminary efficacy studies on the supply to determine its potential use as part of the U.S. stockpile.

If acceptable, HHS' Food and Drug Administration (FDA) would classify the vaccine as an Investigational New Drug available for emergency use, with HHS' Centers for Disease Control and Prevention (CDC) as its sponsor.

Initial results of studies on the effectiveness of the Aventis supply are very encouraging, but the Secretary cautioned that more studies are still needed. A final agreement to obtain the Aventis product would require that the vaccine being proven safe and effective. The National Institutes of Health (NIH) would conduct clinical trials to confirm its effectiveness.

On Thursday, HHS released results from a key clinical trial that show that the existing U.S. supply of smallpox vaccine - 15.4 million doses - could be diluted up to five times and retain its potency, effectively expanding the number of individuals it could protect from the contagious disease to 77 million.

In addition, HHS has contracts with Acambis Inc. to obtain 209 million doses of new vaccine by the end of this year. The contract gives HHS the option to obtain additional vaccine quickly if needed.

The last case of smallpox occurred in the United States in 1949, and the disease was declared eradicated worldwide in 1980 by the World Health Organization (WHO). Vaccinations to prevent smallpox have not been routinely administered in the United States since 1972, and people vaccinated prior to 1972 very likely have diminished immunity to smallpox.