For centuries, smallpox killed millions of people around the world. But thanks to global immunization programs, the deadly infectious disease was wiped out in the late 1970s.
Today, scientists keep only a small amount of the virus alive under tightly controlled conditions in the U.S. and Russia for medical research.
Routine smallpox vaccinations stopped in the U.S. and in many other countries in 1972, and in all other World Health Organization member countries by 1986. Many adults living today likely got the vaccine as children.
What Causes Smallpox?
The variola virus causes it. There are two forms of the virus. The more dangerous form, variola major, led to smallpox disease that killed about 30% of people who were infected. Variola minor caused a less deadly type that killed about 1% of those who got it.
How Smallpox Is Spread
The disease is highly contagious. You get it mainly by breathing in the virus during close, face-to-face contact with an infected person. It usually spreads through drops of saliva when the person coughs, sneezes, or speaks.
Smallpox also can spread when someone handles the clothes or sheets of an infected person or comes into contact with their body fluids. Very rarely, smallpox has spread among people in small, enclosed spaces, probably through air in the ventilation system. Animals and insects don’t spread the disease.
Once a person is infected with the virus, 7 to 17 days can pass before they have any symptoms. During this time, the person isn’t contagious and can’t spread the virus to others.
An infected person is most contagious once they start having symptoms. He can spread smallpox to others until he is completely symptom-free.
Smallpox gets its name from its most common sign of the disease: small blisters that pop up on the face, arms, and body, and fill up with pus.
Other symptoms include:
- Flu-like fatigue, headache, body aches, and sometimes vomiting
- High fever
- Mouth sores and blisters that spread the virus into the throat
- A skin rash that gets worse in a typical pattern:
- The rash starts with flat red sores that become raised bumps a few days later.
- The bumps turn into fluid-filled blisters.
- The blisters fill with pus.
- They crust over, usually in the second week of smallpox.
- Scabs form over the blisters and then fall off, usually in the third week of the disease. They can cause permanent scars.
- Blindness can happen when blisters form near the eyes.