What Is Smallpox?

Smallpox is a disease caused by a virus. At one time, it was one of the world’s most feared, potentially fatal infections. Smallpox is nearly nonexistent as a result of a worldwide vaccination effort. The last case in the US was in 1949. The last naturally occurring case in the world occurred in 1977. There have been no cases of smallpox reported anywhere. The vaccine is no longer given.

Because of bioterrorism threats, it’s important to remember the facts about smallpox.

Smallpox can be spread from person to person by direct, face-to-face contact. It can also be spread through bodily fluids or linens and clothing that have been contaminated. Smallpox can be spread through the air, although this is rare.

The primary symptoms include:

  • High fever
  • Headache
  • Body aches
  • Vomiting

As the virus advances, a red rash appears on the tongue and in the mouth. The rash then spreads. Spots begin to break open. The rash spreads across the body. It turns from red spots into raised bumps. By day 4, the bumps fill with fluid and have a depression in the middle. Scabs form over all of the bumps.

What Is the Smallpox Vaccine?

The smallpox vaccine contains a live virus, called the vaccinia virus. This is related to smallpox. The vaccine is given as multiple pinpricks usually in the arm.

Who Should Get Vaccinated and When?

You should get the vaccine if you have come in contact with the virus or if you are at risk. The vaccine is not given to the general public. You will get the vaccine if you are in the military and work in high threat areas.

What Are the Risks Associated With the Smallpox Vaccine?

A live virus is injected into the skin. It is possible to spread it to other areas of the body, or even to other people. The injection site must be protected to prevent this from happening.

Common side effects of smallpox vaccine include:

  • Rash and itching
  • Fever
  • Headache
  • Tiredness
  • Swollen lymph nodes
  • Body aches
  • Soreness in the arm

More serious, but less common side effects include:

  • Inflammation of the heart muscle or sac around the heart
  • Swelling of the brain or spinal cord
  • Infection at the site of the vaccine
  • Severe allergic reaction

Who Should Not Get Vaccinated?

The following people should not get vaccinated:

  • People who have had a previous allergic reaction to the vaccine or any of its components
  • Pregnant or breastfeeding women
  • Children less than 12 months old
  • People with eczema or who have had a history of eczema or other skin conditions
  • People with skin conditions, such as burns, chickenpox, shingles, impetigo, severe acne, or psoriasis —wait until healed before getting the vaccine
  • People with heart disease, heart conditions, multiple risk factors for heart disease, or stroke -like symptoms
  • People with weakened immune systems (such as those who have received a transplant, have HIV, are receiving cancer treatment, or are taking medicines that suppress the immune system, including steroids)

Talk to your doctor to find out if the vaccine is safe for you.

What Happens in the Event of an Outbreak?

If an outbreak happens, the US has a large supply of the smallpox vaccine to vaccinate the entire population.


Centers for Disease Control and Prevention

Department of Health & Human Services


Emergency preparedness for vaccine safety. Centers for Disease Control and Prevention website. Available at: https://www.cdc.gov/vaccinesafety/ensuringsafety/monitoring/emergencypreparedness/index.html. Updated October 27, 2015. Accessed December 7, 2017.

Medication guide: Smallpox (vaccinia) vaccine, live. Food and Drug Administration website. Available at: https://www.fda.gov/downloads/BiologicsBloodVaccines/Vaccines/ApprovedProducts/UCM142576.pdf. Accessed December 7, 2017.

Smallpox. Centers for Disease Control and Prevention website. Available at: https://www.cdc.gov/smallpox. Updated July 12, 2017. Accessed December 7, 2017.

Smallpox. EBSCO DynaMed Plus website. Available at:http://www.dynamed.com/topics/dmp~AN~T115102/Smallpox. Updated November 17, 2017. Accessed December 7, 2017.

Last reviewed November 2018 by EBSCO Medical Review Board David L. Horn, MD, FACP  Last Updated: 12/20/2014