Vaccine Safety

This information is about preventing or responding to smallpox. For the latest information about the current mpox outbreak, including information on symptoms, prevention, and vaccines, please visit CDC’s Mpox site.

The smallpox vaccine is the best protection you can get if you are exposed to the smallpox virus. Anyone directly exposed to smallpox, regardless of how healthy they are, would be offered the smallpox vaccine because the risks associated with smallpox disease are far greater than those posed by the vaccine.

There are side effects and risks related to the smallpox vaccine. Most people have normal, usually mild reactions such as a sore arm, fever, and body aches. However, some people may have reactions ranging from serious to life-threatening.

You are more likely to have serious side effects if:

  • You currently have or have ever had certain chronic skin conditions, even if it was only once (especially eczema or atopic dermatitis.)
  • You have active breaks in the skin at the time of vaccination, like poison ivy or acne.
  • You have a weakened immune system. You may have a weakened immune system if you:
    • Have had a transplant.
    • Are HIV-positive.
    • Have cancer or are being treated for cancer.
    • Are taking medications that suppress your immune system, like steroids.
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