Dilution Could Extend Smallpox Vaccine Supply Without Compromising Effectiveness

By MATT CRENSON
AP National Writer
(AP) BOSTON

In the event of a bioterror attack using smallpox, health authorities could stretch out the nation's limited vaccine supply simply by diluting the 15 million doses that are on hand, a government official said Sunday.

Experiments to see whether diluted smallpox vaccine could still offer protection against the disease have been "very successful," said Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases.

Fauci spoke in Boston at the annual meeting of the American Association for the Advancement of Science.

The dilution experiments tested vaccines that had been watered down to as little as one-tenth their original concentration on 650 volunteers. The data available so far do not show definitively that vaccines could be diluted that much and still prevent smallpox. But it is clear that a significant amount of dilution is possible, Fauci said.

Conclusive data were expected in March.

To boost supplies of smallpox vaccine even further, the government has also ordered more than 200 million doses from a British company, to be delivered by the end of 2002. In the event of an attack, health officials would use the new doses first, dipping into the diluted vaccine only if those ran out or had not yet arrived.

The U.S. has no plans to offer widespread smallpox vaccination to the public, because for the time being the vaccine is considered a greater threat than the possibility of an attack.

In rare cases the vaccine causes health complications or death, and some experts estimate that vaccinating the entire American population would kill 400 people and permanently injure thousands more.

The National Institute of Allergy and Infectious Diseases is trying to develop improved smallpox vaccines that do not have harmful side effects, Fauci said.

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