Smallpox

  • Medical Author:
    Mary D. Nettleman, MD, MS, MACP

    Mary D. Nettleman, MD, MS, MACP is the Chair of the Department of Medicine at Michigan State University. She is a graduate of Vanderbilt Medical School, and completed her residency in Internal Medicine and a fellowship in Infectious Diseases at Indiana University.

  • Medical Editor: Charles Patrick Davis, MD, PhD
    Charles Patrick Davis, MD, PhD

    Charles Patrick Davis, MD, PhD

    Dr. Charles "Pat" Davis, MD, PhD, is a board certified Emergency Medicine doctor who currently practices as a consultant and staff member for hospitals. He has a PhD in Microbiology (UT at Austin), and the MD (Univ. Texas Medical Branch, Galveston). He is a Clinical Professor (retired) in the Division of Emergency Medicine, UT Health Science Center at San Antonio, and has been the Chief of Emergency Medicine at UT Medical Branch and at UTHSCSA with over 250 publications.

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Can smallpox be prevented with a vaccine?

There is an effective vaccine for the prevention of smallpox. The vaccine is made from a virus called vaccinia. The similarity between these two names (vaccine and vaccinia) is not coincidental because smallpox was the first disease to be prevented by vaccination. In 2007, a second-generation smallpox vaccine (ACAM2000) was licensed. The vaccine contains live vaccinia virus but does not contain any smallpox virus. It is not a shot and is administered in a unique manner: a sharp, pronged piece of metal is dipped in the vaccine and then used to prick the skin of the recipient. This is done several times. If successful, the site of vaccination will develop small blisters that scab and heal, leaving a scar. This process is called scarification. While the blisters are active, the site should be kept clean, dry and covered to prevent the vaccinia virus from spreading to others.

Many older adults still have a vaccine scar on their arms from being vaccinated when they were younger. Smallpox vaccine, like other live vaccines including the yellow fever vaccine, teaches the body's immune system to remember how to make antibodies. There may still be a level of protection, even decades after vaccination. However, revaccination would be recommended in the event of a smallpox exposure. Interestingly, vaccination after exposure provides some protection against severe disease.

Vaccination is no longer recommended for the general population because the disease has been eradicated. Currently, the vaccine is given only to selected military personnel and laboratory workers who handle the smallpox virus.

Vaccination side effects are uncommon but are sometimes serious and potentially fatal. Because the vaccine contains live vaccinia virus, the virus may spread and infect the heart, causing myocarditis (infection of the heart muscle) or pericarditis (infection of the sac around the heart). This occurs in approximately one in 175 adults who are vaccinated for the first time. The vaccine can also infect the brain (encephalitis) or eye or cause a generalized rash. Vaccine complications lead to death in approximately six people for every million people who are newly vaccinated. Complications are much less common in revaccination. People with weak immune systems and those with skin conditions like eczema are at higher risk for complications. Pregnant women should not be vaccinated because of the risk of fetal death.

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