A week after she was given an experimental dose of smallpox vaccine, Elizabeth Forrester's arm became swollen, her head throbbed and she felt tired and feverish.
"At one point I was like 'cut it off, please cut off my arm,'" she recalled telling her husband when the pain kept her from sleeping.
Forrester, a 26-year-old graduate student, was one of 148 people to receive the vaccine in a government study at Vanderbilt University.
Her reaction may be a preview of what hundreds of thousands of people might experience as federal officials prepare to offer the vaccine widely for the first time in three decades.
About 10 percent of the Vanderbilt subjects — all healthy and between the ages of 18 and 30 — experienced extreme discomfort, with fatigue, fever, loss of appetite and other flu-like symptoms that lasted a day or two, Dr. Tom Talbot said.
In a smaller pilot study at Vanderbilt last summer, about 30 percent reported illness severe enough to miss work or school.
The study, which began in October and ends next month, is part of a federal effort to protect the nation from a biological attack using smallpox. The virus is supposed to exist only in special labs in Moscow and Atlanta, but experts fear it has been obtained by hostile nations or terrorist groups.
Similar studies were held around the country last summer to test the safety and potency of two vaccines, Aventis-Pasteur and Dryvax, that in some cases were stored for as long as 40 years.
A study is now under way at the University of Iowa, and a University of Cincinnati study on how the vaccine will affect children awaits government approval.
President Bush is expected to announce plans soon for offering the vaccine to the public, beginning with about 500,000 hospital workers and expanding to as many as 10 million police, fire and emergency workers.
States, cities and territories were asked to submit their plans for the first stage of smallpox vaccinations by Monday to the federal government; most met the deadline.
The vaccine was routinely given to children in this country until 30 years ago. Talbot said its side effects alarm a generation of Americans unaccustomed to them.
"Our vaccines are so safe nowadays," he said. "When we get a flu shot, if we get a sore arm we get a little upset."
Most modern vaccines, such as the flu shot, use dead versions of the virus they try to protect against. The smallpox vaccine, however, is made with a live virus called vaccinia that is related to smallpox but much milder.
Still, for every million people being vaccinated for the first time, between 15 and 50 will suffer life-threatening side effects such as brain inflammation — and one or two will die, historical data shows. Side effects were less severe for those being revaccinated.
Smallpox vaccinations were stopped in the United States in 1972 because the virus, the source of one of the deadliest scourges on earth, was believed eradicated.
In New Orleans, American Medical Association delegates approved a resolution Wednesday backing federal recommendations for smallpox vaccinations. However, the resolution called for some sort of liability protection set up by the government before the first shot is given.