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Smallpox Vaccine

Medically reviewed by Last updated on Feb 6, 2023.

What is a smallpox vaccine?

A smallpox vaccine is an injection given to help prevent smallpox. Two vaccines are currently available. The vaccines also protect against mpox (also called monkeypox). Smallpox and mpox are similar diseases caused by different but related viruses. To be most effective, vaccination should happen within 4 days of exposure. Vaccination 4 to 14 days after exposure will not prevent infection but can prevent severe symptoms.

Who should get a smallpox vaccine?

The vaccines are not part of the usual vaccination schedule because the risk of disease is low. Only certain people should receive a vaccine, such as those who would take action during a smallpox outbreak. You should get the vaccine or booster doses if you are any of the following:

  • A healthcare provider who may treat or be in close contact with those who could have smallpox
  • A laboratory worker who handles the smallpox virus or other pox viruses
  • A military or other staff member who may be sent to areas with smallpox threat

Who should not get a smallpox vaccine?

The following should not get a smallpox vaccine unless directed by a healthcare provider:

  • Infants younger than 12 months
  • Anyone who had an allergic reaction to the vaccine or to the antibiotics neomycin, streptomycin, polymyxin B, or chlortetracycline
  • Anyone who is pregnant or breastfeeding
  • Anyone with immune system problems, leukemia, lymphoma, cancer, HIV, or AIDS
  • Anyone who has a heart condition or a skin condition such as eczema or psoriasis
  • Anyone who had a bone marrow or organ transplant
  • Anyone who uses medicines that weaken the immune system, such as steroids, radiation, or cancer medicines

What happens when I receive a smallpox vaccine?

The 2 available vaccines are given in different ways:

  • One vaccine is given with a needle that has been dipped into the vaccine solution. The needle pricks the skin on your upper arm and leaves a droplet of the vaccine when it is removed. Pricking is done a number of times over a few seconds. This causes a sore spot and small blood droplets to form. You are considered fully vaccinated 28 days after you receive this vaccine.
    • Your skin will react to the vaccine over the next 3 to 4 weeks. Within 5 days, a small bump forms on the area where the vaccine was given. Within 10 days, the bump becomes filled with fluid and pus, and reaches its biggest size. Within 21 days, the bump dries up and forms a scab. The scab then falls off after 3 to 4 weeks and leaves a scar.
    • The virus can be spread before the scab falls off. Contact with the vaccinated area may easily spread the virus to other parts of your body. You may also spread the virus to other people through direct contact. You will need to cover the area with a bandage until the scab falls off. Your healthcare provider will give you a full list of instructions for preventing the virus from spreading.
    • Booster (additional) doses may be recommended every 3 years. Boosters are recommended for anyone who continues to be at high risk for smallpox. Your healthcare provider can tell you if you should get a booster, and when to get it.
  • The other vaccine is given in 2 shots. The second shot is given 4 weeks after the first. You are considered fully vaccinated 2 weeks after your second shot.
    • You will not need to take precautions. You are not at risk of spreading the virus to others from this vaccine.
    • Booster (additional) doses may be recommended every 2 or 10 years. Boosters are recommended for anyone who continues to be at high risk for smallpox. Your healthcare provider can tell you if you should get a booster, and when to get it.

Treatment options

The following list of medications are in some way related to or used in the treatment of this condition.

What are the risks of smallpox vaccination?

The area where the vaccine was given may be red, tender, or swollen. You may get a fever, mild rash, or swollen glands in your armpits. You can spread the virus in the vaccine to other people by accident. The area where the vaccine was given may get infected. The infection may spread to your eyes, heart, or brain. This can cause long-term damage. You may have an allergic reaction to the vaccine. This can be life-threatening.

Call your local emergency number (911 in the US) for any of the following:

  • Your mouth and throat are swollen.
  • You are wheezing or have trouble breathing.
  • You have chest pain or your heart is beating faster than normal for you.
  • You feel like you are going to faint.

When should I seek immediate care?

  • Your face is red or swollen.
  • You have hives that spread over your body.
  • You feel weak or dizzy.

When should I call my doctor?

  • You have a fever and a headache.
  • You have swollen lymph glands in your armpits.
  • You think the virus has spread to another part of your body.
  • Your wound from the vaccine gets larger or does not heal.
  • You have questions or concerns about smallpox vaccination.

Care Agreement

You have the right to help plan your care. Learn about your health condition and how it may be treated. Discuss treatment options with your healthcare providers to decide what care you want to receive. You always have the right to refuse treatment. The above information is an educational aid only. It is not intended as medical advice for individual conditions or treatments. Talk to your doctor, nurse or pharmacist before following any medical regimen to see if it is safe and effective for you.

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Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.