The findings were reported Thursday at the CDC's Advisory Committee on Immunization Practices (ACIP) smallpox working group meeting taking place here.

"Physicians think of the vaccine as being as safe as current childhood vaccines, and it's not quite that safe," Dr. Glen Nowak, the CDC's Associate Director of Health Communications, told Reuters Health in a phone interview.

Most younger doctors have had no experience in administering the smallpox vaccine, since routine vaccinations were stopped in the US in 1972.

Side effects from vaccination include death in about 0.5 to 5 per million who receive it, encephalitis, and moderate to severe lesions at or away from the site of vaccination.

According to Dr. Nowak, doctors were not only unfamiliar with the side effects, but were also uncertain about "ring vaccination," a strategy of limiting vaccine delivery to only the people who most need it, such as those who have had contact with infected persons or their contacts.

"The ring strategy is in contrast to the normal strategy for delivering childhood vaccines, for which the goal is to deliver vaccine to at least 90% of people," Dr. Nowak said.

The survey involved in-depth interviews with 17 physicians in Philadelphia, Chicago, and San Francisco. Another part of the study involved 20 public focus groups of about eight people each to gauge the public's attitude towards receiving the vaccine.

The current policy says that only a handful of people who work with the virus should be vaccinated, and the groups were asked whether this policy should be changed.

According to Dr. Nowak, most people were interested in whether the vaccine would be nearby if and when they needed it. "We also found out that if there was an outbreak, most people would be interested in getting it immediately," he said.

The ACIP is currently formulating an updated set of recommendations to be presented at a meeting on June 19 and 20.

Before this meeting the researchers "will be trying to get input on a number of things including how the vaccine should be used before there is any kind of outbreak or attack and how it should be used in the event of an attack," Dr. Nowak said.