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smallpox overview

Last Updated:
21 May 15

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If you have clinical questions related to vaccination, please contact the DoD Vaccine Clinical Call Center at 1-866-210-6469.

Expected responses and Side Effects

All vaccines cause side effects, but smallpox vaccine causes a unique response at the vaccination site.

After smallpox vaccination, a red blister appears that should turn white 6 to 8 days after vaccination. Then it will turn into a scab. This shows successful vaccination.

If your vaccination site does NOT look like the pictures shown in your briefing, come back to your clinic or provider for follow-up.

Most people experience normal, usually mild, reactions, such as sore arm, swollen lymph nodes, fever, headache, body ache, and fatigue. These symptoms may peak 8 to 12 days after vaccination.

  • Most people feel a stinging or burning sensation right after vaccination that lasts less than a minute.
  • The lymph nodes in the armpit of the vaccinated arm or in the neck may become large and painful for a week or so.
  • The vaccination site should become tender, red, and itchy. A blister will form there, and then fill with pus. When the scab dries and falls off on its own, after about 2 to 3 weeks, a permanent scar remains.

No Reaction?
In a few percent of previously unvaccinated individuals, appropriate vaccination techniques may result in no response. Do not assume that you are immune. Contact your vaccination provider to arrange a repeat vaccination.

Serious Side Effects

In the past, about 1,000 out of every 1,000,000 (one per thousand) vaccinated people experienced reactions that were serious, but not life-threatening. Most of these reactions involved spread of vaccine virus elsewhere on the body.

In the past, between 14 and 52 people out of 1,000,000 vaccinated for the first time experienced potentially life-threatening reactions. These reactions included serious skin reactions and inflammation of the brain (encephalitis).

As of January 2008, DoD has identified 161 cases of acute myocarditis and/or pericarditis among 1.4M smallpox vaccinees, with symptoms appearing 7 to 19 days after vaccination. These people had clinical conditions that varied from mild to moderate; the condition was severe in two cases. Most cases occurred among those recieving smallpox vaccinations for the first time. Most cases occurred among men. These cases were followed carefully to evaluate their recovery, at 27 hospitals in 21 states and several countries overseas. Based on our data and European experience, we have reason to believe these people should recover and remain well.

Serious side effects are generally more common after first vaccination; revaccination results in fewer serious side effects.

DoD carefully screens potential smallpox vaccine recipients and exempts people with compromised immune systems, people who have (or had) certain skin conditions, and people with certain cardiac risk factors to reduce the risk of serious adverse events.