New Web site explains risks of smallpox and related vaccine

January 8, 2003

GAINESVILLE, Fla. — What do a lottery ticket and a smallpox vaccination have in common?

Before getting either one you need to understand the odds it will pay off, says University of Florida smallpox expert Dr. Parker Small Jr., a professor of pathology, immunology and laboratory medicine with UF’s College of Medicine.

Small and risk assessment specialist John Paling, a UF environmental toxicologist, have set up a new Web site to help people concerned about smallpox bioterrorism evaluate the risk posed by the viral disease and the vaccine intended to prevent it.

“Our main point is that all people are not at equal risk,” Small said. “Where someone lives and whether they have been vaccinated before determines how much they should worry. This Web site offers a visual tool to help individuals assess their own risk.”

The site is located at http://ccl.ichp.edu/smallpox.

Smallpox vaccinations currently are available only to military, law enforcement and medical personnel, but the federal government has developed a voluntary program for the general public that could be implemented in 2004.

“It is very important to recognize that the U.S. government and especially its public health departments are prepared right now to vaccinate anyone and has enough vaccine for everyone were smallpox to break out,” Small said.

The vaccine once was routinely administered to children but has not been used in the United States since 1972 because efforts to control the disease were so successful, Small said.

Using data gathered in previous studies from around the world, Small estimates that in a smallpox attack large enough to infect 1,000 U.S. residents, people younger than 30 who live in major cities and have never been vaccinated would have a one in 85,000 chance of becoming infected. If infected and left untreated, their risk of dying would be one in 250,000, a mortality rate of approximately 30 percent.

For people older than 30 who have been vaccinated previously and do not live in major cities, the odds of becoming infected would be about one in 100 million, Small said. If infected and left untreated, their risk of dying would be one in 1.7 billion, a mortality rate of approximately 6 percent.

Compare that to the odds of winning one of the weekly Florida Lotto drawings, which are about 1 in 23 million, according to the Florida Lottery.

The odds of dying from a first-time administration of smallpox vaccine are about one in 500,000, Small said. People with compromised immune systems are at much greater risk of harm from the vaccine and should consult a physician if considering vaccination.

On the Web site, examples of the relative risks of the disease and the vaccination are presented in an easy-to-follow chart known as the Paling Perspective Scale, which Paling designed.

“I am sure the public would appreciate a more clear explanation of what their odds are, according to their specific circumstances,” Paling said. “To the best of our knowledge, this is the first time anyone has tried to show the public these issues in a visually understandable way.”

Small said there is no risk of developing smallpox as long as there is not a terrorist attack using smallpox as a weapon.

“If there’s a smallpox terrorist attack, those people exposed in the initial attack will probably not know it until the symptoms develop about two weeks later,” Small said.

Smallpox is moderately contagious, transmitted when people encounter the virus on surfaces or in the air. Once a person is infected, the disease incubates for about two weeks then produces symptoms that include fever, headache, backache, malaise, fever and perhaps vomiting. After two or three days of these symptoms, a bumpy rash appears on the face and extremities.

People who have been infected can only transmit the disease after the rash appears when they are likely to be seriously and noticeably ill, Small said.

“They will not be out wandering the streets spreading the virus, they will be in bed,” he said. “Only the people caring for them will be at risk.”

If an attack occurred, smallpox vaccine administered within two or three days after exposure should be close to 100 percent effective in stopping the disease, Small said. Scientists are still debating whether the window of opportunity may last longer, especially for those who have been previously vaccinated.

The new Web site could generate controversy because not all scientists agree on how best to handle the issue of vaccination, Paling said. The site includes a downloadable Paling Perspective Scale, on which users can fill in their own data and submit their own calculations of the risks.

“I believe this will be the single biggest health-care communications issue of the next 12 to 15 months,” he said. “I don’t think it should be controversial in America to try to have an academic discussion in a way that the public can look over the scientists’ shoulders and see what the points of difference are in order to help ‘we the people.’”