What is the smallpox vaccine, and is it still required?
The smallpox vaccine is the only way to prevent smallpox. The vaccine is made from a virus called vaccinia, which is another "pox"-type virus related to smallpox but cannot cause smallpox. The vaccine helps the body develop immunity to smallpox. It was successfully used to eradicate smallpox from the human population.

Routine vaccination of the American public against smallpox stopped in 1972 after the disease was eradicated in the United States. Until recently, the U.S. government provided the smallpox vaccine only to a few hundred scientists and medical professionals who work with smallpox and similar viruses in a research setting.

How is the vaccine given?
The smallpox vaccine is not given with a hypodermic needle. It is not an injection, unlike many vaccinations. The vaccine is given using a bifurcated (two-pronged) needle that is dipped into the vaccine solution. When removed, the needle retains a droplet of the vaccine. The needle is then used to prick the skin a number of times in a few seconds. The pricking is not deep, but it will cause a sore spot and one or two drops of blood to form. The vaccine usually is given in the upper arm.

If the vaccination is successful, a red and itchy bump develops at the vaccination site in three or four days. In the first week after vaccination, the bump becomes a large blister, fills with pus, and begins to drain. During week two, the blister begins to dry up and a scab forms. The scab falls off in the third week, leaving a small scar. People who are being vaccinated for the first time may have a stronger "take" (a successful reaction) than those who are being revaccinated.

How safe is the smallpox vaccine?
The smallpox vaccine is the best protection you can get if you are exposed to the smallpox virus. Most people experience normal, usually mild reactions that include a sore arm, fever, and body aches. In recent tests, one in three people felt bad enough to miss work, school, or recreational activity or had trouble sleeping after receiving the vaccine.

However, the vaccine does have some risks. In the past, about 1,000 people for every 1 million people vaccinated for the first time experienced reactions that, while not life-threatening, were serious. These reactions include a vigorous (toxic or allergic) reaction at the site of the vaccination and spread of the vaccinia virus (the live virus in the smallpox vaccine) to other parts of the body and to other people. These reactions typically do not require medical attention. Rarely, people have had very bad reactions to the vaccine. In the past, between 14 and 52 people per 1 million vaccinated experienced potentially life-threatening reactions, including eczema vaccinatum, progressive vaccinia (or vaccinia necrosum), or postvaccinal encephalitis. Based on past experience, it is estimated that between 1 and 2 people out of every 1 million people vaccinated will die as a result of life-threatening reactions to the vaccine. Careful screening of potential vaccine recipients is essential to ensure that those at increased risk do not receive the vaccine.

People most likely to have side effects are:

• People who have, or even once had, skin conditions (especially eczema or atopic dermatitis)
• People with weakened immune systems, such as those who have received a transplant, are HIV positive, or are receiving treatment for cancer.

Who should NOT get the vaccine?

• Anyone who is allergic to the vaccine or any of its components.
• Anyone with a weakened immune system (HIV patients, cancer patients, steroid users or those prescribed immunosuppresive drugs).
• Pregnant women, because of the risk it poses to the fetus.
• Women who are breastfeeding.
• Children younger than 12 months of age.
• The Advisory Committee on Immunization Practices (ACIP) advises against non-emergency use of smallpox vaccine in children younger than 18 years of age.

Anyone who falls within these categories, or lives with someone who falls into one of these categories, should not get the smallpox vaccine unless they are exposed to the disease.

For more information, see the CDC's contraindications page.

Where can I find out more?

Details of adverse reactions to the disease may be seen on the CDC's illustrated guide to adverse vaccine reactions .