What is smallpox?

Smallpox is a serious, life-threatening illness caused by the variola virus. It causes pus-filled blisters (pustules) to develop on your skin. In 1980, the World Health Organization (WHO) declared that smallpox was eradicated (wiped out). Since then, there haven’t been any naturally occurring confirmed cases of smallpox.

Before being eradicated, millions of people died from this highly contagious disease. A vaccine protects against smallpox, but vaccinating the general public isn’t recommended because of concerns about the vaccine’s side effects.

How common is smallpox?

There haven’t been any confirmed cases of smallpox since it was wiped out. Before that, smallpox was a life-threatening disease. Millions of people got smallpox every year. Up to 30% of people died of their illness. Death was due to systemic shock (body-wide infection) and toximemia (toxins in the blood). Smallpox is a very contagious disease, with secondary attacks affecting up to 80% of household contacts. Often, people who survived the disease had long-term problems, such as blindness and severe scarring.

Researchers believe that the disease first appeared in the third century. For thousands of years, smallpox spread throughout the world. In the 1960s, the WHO led a worldwide effort to eliminate smallpox.

Could smallpox come back?

Scientists saved samples of the variola virus (the virus that causes smallpox) so they could continue to research vaccines and treatments. Only two locations in the world have these virus samples. They’re secured at the U.S. Centers for Disease Control and Prevention (CDC) in Atlanta and the State Research Center of Virology and Biotechnology (VECTOR Institute) in Russia.

As smallpox no longer occurs naturally, public health officials are only concerned about it spreading as a result of biological warfare. There haven’t been any immediate threats of terrorists using smallpox as a weapon, but scientists are prepared to respond if someone weaponizes smallpox. The CDC has created enough smallpox vaccine to protect everyone in the United States if the virus does resurface.

Symptoms and Causes

What are the symptoms of smallpox?

Smallpox symptoms don’t appear right away. A person may not look or feel sick for about seven to 14 days after exposure to the variola virus. This time is the incubation period. At the end of the incubation period, the first symptoms appear.

Smallpox can present as four clinical types. The most common form — known as ordinary smallpox — occurs in 90% of the cases. Other types include flat smallpox, hemorrhagic smallpox and vaccine-modified smallpox.

Stages of the most common form of smallpox are as follows:

Initial symptoms: This stage lasts about three days. Symptoms include high fever, muscle aches, backaches, headaches and vomiting.

Early rash: After the initial symptoms, a body-wide rash appears. You’re most contagious during this stage. The virus can spread easily through talking, sneezing or coughing. During the early rash stage:

  1. A rash develops on your tongue and inside of your mouth and throat. Red spots in your mouth become sores, which break open.
  2. The rash spreads to your face and then your arms, legs, back and torso. The rash takes about a day to spread all over your body, including the palms of your hands and the soles of your feet.
  3. Bumps on your skin fill with pus (thick fluid). There may be a dent in the middle of each bump. It takes about two days for the bumps to fill with fluid.

Pustular rash and scabs: Bumps turn into pustules (firm, round lumps). Over the next 10 days, crusty scabs form over the pustules. About a week later, scabs start to fall off.

The scabs typically fall off in about three weeks. When they fall off, they leave scars. A person with smallpox is contagious until the last scab has fallen off.

What causes smallpox? How does it spread?

The variola virus causes smallpox. In the past, people spread smallpox most commonly through direct, prolonged face-to-face contact with others. When they sneezed or coughed, they would send respiratory particles through the air. When other people inhaled these large droplets, they would become infected. Less commonly, people become infected by direct contact with the rash or crust material from a swab.

People also spread the virus to each other by sharing sheets, towels and clothing. The disease is most contagious when sores first appear in your throat and mouth. But a person with smallpox is contagious for several weeks after the first sores develop.

Diagnosis and Tests

How is smallpox diagnosed?

As smallpox no longer occurs naturally, a smallpox diagnosis today is very unlikely. Any symptoms are probably signs of another condition or illness. Before eradication, smallpox was easy to recognize, but few other common illnesses, such as severe chickenpox, were misdiagnosed as smallpox.

Management and Treatment

Can smallpox be treated with medication?

There isn’t a cure for smallpox. Researchers believe some antiviral drugs may make the illness less severe. But providers aren’t sure how effective these treatments would be. They haven’t used the drugs to treat smallpox in the past.


What’s the status of a vaccine to prevent smallpox if it ever reemerged?

Although vaccines can protect people from smallpox, they aren’t available to the general public. Only people who work in a lab with the variola virus (and similar viruses) should get the vaccine. The vaccine is generally safe. But it has caused severe side effects and complications, such as heart problems and even death.

As there haven’t been any cases of smallpox since the late 1970s, healthcare providers don’t believe the risks of side effects are worth vaccinating everyone. If a smallpox outbreak occurred, the CDC has enough smallpox vaccine to give to everyone in the United States.

Outlook / Prognosis

What is the outlook for people with smallpox?

Before 1980, around 30% of people with smallpox died from the disease. Most people who survived smallpox had severe scarring after scabs from the blisters fell off. Smallpox also caused blindness when ulcers formed on the eyes.

If someone got smallpox today, antiviral drugs would likely decrease the severity of the illness. But as researchers developed these drugs after smallpox was wiped out, they’ve never used them to treat a person with smallpox. Still, international health authorities are prepared to respond quickly to keep people safe if smallpox ever comes back.

Living With

If I develop a rash, is there any chance it’s smallpox?

It’s extremely unlikely that anyone would have smallpox today. Your symptoms are probably due to another condition or disease. Certainly, make an appointment with your healthcare provider if you develop a rash.

A note from Cleveland Clinic

Smallpox was eradicated (wiped out) decades ago. You don’t need to be concerned about getting this disease from others. Though very unlikely, a bioterrorist attack involving smallpox could expose people to the virus. But the CDC, along with local and state health departments, has been preparing for this type of emergency for years. These organizations have enough smallpox vaccine to protect everyone in the U.S. in the unlikely event that smallpox reemerges.

Last reviewed by a Cleveland Clinic medical professional on 12/06/2020.


  • Centers for Disease Control and Prevention (CDC). History of Smallpox. ( Accessed 12/6/2020.
  • Centers for Disease Control and Prevention (CDC). Signs and Symptoms. ( Accessed 12/6/2020.
  • National Institute of Allergy and Infectious Disease. Smallpox. ( Accessed 12/6/2020.
  • National Organization for Rare Disorders. Smallpox. ( Accessed 12/6/2020.

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