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Smallpox Vaccine

By William D. Surkis, MD, Clinical Associate Professor of Medicine, Jefferson Medical College; Director, Internal Medicine Residency Program, Lankenau Medical Center
Jerome Santoro, MD, Clinical Professor of Medicine, Jefferson Medical College; Chief, Department of Medicine, Lankenau Medical Center

The smallpox vaccine has not been routinely given in the United States for 30 years because the disease has been eliminated. Because the vaccine’s protective effects wear off after about 10 years, most people are now susceptible to smallpox.

Recent fears about the possible use of smallpox by terrorists have led to the suggestion that smallpox vaccination resume. If smallpox vaccination is resumed, it is likely to be recommended only for people in the area of a smallpox outbreak. Some military personnel are now vaccinated (based on their risk of exposure if smallpox were to be used as a biological weapon), and enough smallpox vaccine has been prepared to vaccinate everyone in the United States if needed.

The smallpox vaccine contains live vaccinia virus, which is related to and provides immunity against the smallpox virus. Two formulations are available.

The vaccine is most effective when given very early after exposure. However, the vaccine may also be beneficial if given in the first days after symptoms appear. There is no treatment for smallpox.


To administer the smallpox vaccine, doctors rapidly jab a small area 15 times with a needle that has been dipped in the vaccine. Then the vaccine site is covered with a dressing to prevent the vaccina virus from spreading to other body sites or to other people.

Vaccination is considered successful if a small blister develops about 7 days later. If vaccination is successful, only one dose is given. If it is not, people are given another dose.

Side Effects

The vaccine is generally safe. Fever, a general feeling of being ill (malaise), and muscle aches are common the week after vaccination.

Serious side effects occur in about 1000 of every million previously unvaccinated people, and death occurs in 1 or 2 per million. The risk of serious side effects and death is lower in previously vaccinated people.