MSD Manual

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Smallpox Vaccine


Margot L. Savoy

, MD, MPH, Lewis Katz School of Medicine at Temple University

Last full review/revision Aug 2019| Content last modified Aug 2019
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In the United States, routine vaccination with the smallpox vaccine was stopped in 1972 because smallpox had 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.

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 proven treatment for smallpox, but some antiviral drugs (such as cidofovir) may help treat it or prevent it from getting worse.

For more information, see Centers for Disease Control and Prevention's (CDC) Smallpox: Prevention and Treatment statement.


To administer the smallpox vaccine, doctors rapidly jab a small area 15 times with a specially designed 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 smallpox 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 1 of every 10,000 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.

More Information

NOTE: This is the Consumer Version. DOCTORS: Click here for the Professional Version
Click here for the Professional Version
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