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To prevent the spread of smallpox, healthcare providers must

  • Isolate infected people
  • Vaccinate close contacts of infected people


The currently licensed smallpox vaccine, which consists of a laboratory strain of vaccinia virus, is highly effective in preventing infection. Medical experts believe the vaccine may lessen the severity of, or even prevent, illness in unvaccinated people if given within 4 days of exposure to the virus.

The smallpox vaccine helps the body develop immunity to smallpox. The vaccine is made from a "pox"-type virus related to smallpox. The smallpox vaccine contains live vaccinia virus-unlike many other vaccines that use killed virus. The vaccine does not contain the smallpox virus and cannot transmit smallpox. Learn more about the smallpox vaccine from the Centers for Disease Control and Prevention (CDC).

Few data exist showing just how long vaccinia vaccines protect people against smallpox infection. Therefore, those vaccinated against the smallpox virus before 1972 may be susceptible to the disease. Military and other high-risk groups (for example, scientists who work with vaccinia and other orthopoxviruses related to Variola major) have been getting the vaccine since the United States stopped routine smallpox vaccinations in 1972.

Getting the vaccine

Healthcare providers do not use a hypodermic needle, usually used for vaccinations, to give the smallpox vaccine. Instead, they use a tiny, two-pronged needle that is dipped into the vaccine solution. When removed from the solution, the needle keeps a droplet of the vaccine. The needle is used to prick the skin, usually in the upper arm, a number of times within a few seconds. The pricking is not deep, but it will cause a sore spot and one or two droplets of blood.

If the vaccination is successful, a red and itchy bump develops at the vaccine site in 3 or 4 days.

  • In the first week, the bump becomes a large blister, fills with pus, and begins to drain.
  • During the second week, the blister begins to dry up and a scab forms.
  • In the third week, the scab falls off, leaving a small scar.

People who get the vaccine for the first time have a stronger reaction than those who are revaccinated.

Reactions and complications

Most people experience normal, typically mild reactions to the vaccine, which go away without treatment. The vaccine often causes a low fever, swollen glands in the armpits, as well as skin redness at the vaccination site.

The vaccine, however, can cause several complications, some life-threatening, particularly in people with immune deficiencies and skin disorders. Based on reactions to smallpox vaccines in the past, the CDC estimates that between 14 and 52 out of every 1 million people vaccinated for the first time will have potentially life-threatening complications that require medical attention, including

  • Eczema vaccinatum (EV)-spread of vaccinia skin lesions to areas of the body once or presently afflicted by eczema
  • Progressive vaccinia-uncontrolled spread of the vaccinia virus to adjacent and underlying tissues resulting in tissue death
  • Postvaccinal encephalitis-spread of the vaccinia virus to the central nervous system that is probably made worse by an over-response to the vaccine by the immune system
  • Myo/pericarditis-an inflammation of the heart that is probably also caused by an over-response to the vaccine by the immune system

CDC estimates 1 or 2 in 1 million people who receive the vaccine may die as a result of vaccination. Because of serious and potentially deadly reactions, health care providers must carefully screen potential vaccine recipients to ensure that those at increased risk do not receive the vaccine.

Healthcare providers treat certain serious complications with anti-vaccinia immune globulin-pooled antibodies taken from people recently immunized with the smallpox vaccine. A government-funded program to produce sufficient anti-vaccinia immune globulin to treat all predicted cases of complications has recently been completed.

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Last Updated October 01, 2007