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What Is Smallpox?

Smallpox is an infection caused by the variola virus.

Smallpox caused millions of deaths before a vaccine was created against it. Thanks to widespread vaccination, smallpox was wiped out — the first and only time in history that an infectious disease was eliminated from the planet.

Should We Still Worry About Smallpox?

Although smallpox infection was wiped out many years ago, samples of the variola virus that causes smallpox were saved in laboratories. Some people worry that terrorists could try to get these virus samples with the aim of spreading smallpox infection. But the two research labs that keep the samples are secure and heavily guarded.

In case of a smallpox emergency, the smallpox vaccine would prevent the spread of disease because it can:

  • prevent people from becoming infected if they're vaccinated quickly after exposure to the virus
  • make the illness less severe in people who do become infected if they're vaccinated within a few days

Public health officials have a rapid response plan for vaccinating anyone exposed to the disease and people who have contact with them. So even though they're not needed now, the vaccines are ready.

Because vaccines can stop the spread of the disease, experts believe it's unlikely that terrorists will go to the trouble of making and using smallpox as a biological weapon — it would take too long and have little effect.

What Are the Signs of a Smallpox Infection?

If someone becomes infected with smallpox, it may take anywhere from 7 to 19 days for symptoms to start. At first a person may have flu-like symptoms such as high fever, tiredness, headaches, body aches, and sometimes vomiting.

Within 2 to 3 days after symptoms start, a rash develops. It typically affects the face, legs, and arms. It starts with red marks that get filled with pus and then crust over. Scabs develop and then fall off after about 3 to 4 weeks.

Is Smallpox Contagious?

Smallpox is very contagious, especially when a person has the rash. Most often, it spreads through infected drops of saliva (spit) when people cough or sneeze. It can also spread by contact with the rash or with items (like clothing or bedding) that touched the rash. Someone is contagious until after all the scabs have fallen off.

How Is Smallpox Treated?

Antibiotics don't work against viruses — they're only effective against bacteria — so taking them won't help someone with smallpox. Vaccination is the best way to stop the spread of smallpox. Immunization successfully wiped out smallpox before and, should it be needed, can help stop any future outbreaks. Researchers are also working to develop other treatments too.

It's very unlikely that you or your child will ever be exposed to the virus that causes smallpox. But if you're worried about it, talk to a medical professional, who can help you find the answers to your questions.

Reviewed by: Larissa Hirsch, MD
Date Reviewed: Jun 1, 2022

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