Filed at 9:25 p.m. ET

SAN FRANCISCO (AP) -- The American Medical Association on Tuesday refused to endorse smallpox vaccinations for all Americans, rejecting calls from doctors who say the disease could be used as a biological weapon.

Instead, the 538 delegates attending the AMA's annual winter meeting in San Francisco voted overwhelmingly to continue studying the possible repercussions of such a mass inoculation.

``We do not yet know that the bad guys have the smallpox virus,'' said Dr. Ron Davis, a public health expert from Detroit and a member of the AMA's 16-member board of trustees. ``There are huge, complex issues involved and due deliberation is needed.''

Some doctors said they worry the vaccine itself could kill as many as 300 people if the entire U.S. population were vaccinated. There's also disagreement about whether those already inoculated would need another vaccination to prevent a smallpox infection.

Babies younger than 1 and people with weakened immune systems couldn't withstand smallpox vaccinations, doctors said.

A nationwide smallpox vaccination program was discontinued in 1972, and the disease was eradicated worldwide by 1980. Two smallpox virus samples remain -- one in the United States and the other in Russia. Concerns about security at the Russian lab have been exacerbated by the recent anthrax cases.

Smallpox is contagious, and roughly 30 percent of those who contract it die.

Last week, the Centers for Disease Control and Prevention issued a report recommending that no vaccinations should be given unless an outbreak occurs.

The CDC recommended a technique called ``ring vaccination,'' in which only healthy people around a smallpox victim would receive the vaccine.

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On the Net:

http://www.cdc.gov

http://www.ama-assn.org

ALL INFORMATION, DATA, AND MATERIAL CONTAINED, PRESENTED, OR PROVIDED HERE IS FOR GENERAL INFORMATION PURPOSES ONLY AND IS NOT TO BE CONSTRUED AS REFLECTING THE KNOWLEDGE OR OPINIONS OF THE PUBLISHER, AND IS NOT TO BE CONSTRUED OR INTENDED AS PROVIDING MEDICAL OR LEGAL ADVICE.  THE DECISION WHETHER OR NOT TO VACCINATE IS AN IMPORTANT AND COMPLEX ISSUE AND SHOULD BE MADE BY YOU, AND YOU ALONE, IN CONSULTATION WITH YOUR HEALTH CARE PROVIDER.