What Is Smallpox?

Smallpox is a contagious disease caused by a virus that’s no longer found in nature.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.

Smallpox Symptoms

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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:

  • 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.

Smallpox Causes

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.

Two forms of smallpox were more deadly than the common strain: Hemorrhagic and malignant.

Hemorrhagic smallpox tended to affect adults, including blood-tests' target='_blank' rel='noopener noreferrer' >pregnant women, not children. People had more serious symptoms, including fever, pain, and headaches, and they leaked blood from their blisters and mucous membranes. People usually died of blood poisoning within a week.

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Malignant smallpox tended to affect children, not adults. Instead of raised blisters, people developed flat lesions that merged on the skin surface. Most people who got this form of smallpox also died of blood poisoning.

How Smallpox Is Spread

The disease is highly contagious. You could get it:

  • 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.
  • By handling the clothes or sheets of an infected person or coming 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.
  • If the virus were spread through an act of terrorism. This is a rare possibility, but in case it happens, governments around the world have stockpiled smallpox vaccines.

Smallpox Diagnosis

Because smallpox hasn’t been diagnosed in decades, it’s likely that doctors wouldn’t recognize the disease in patients right away. It’s possible to diagnose the condition by testing a sample of tissue taken from a smallpox blister. A single diagnosis would be considered a worldwide health emergency.

Smallpox Treatment

There’s only one known drug that can treat smallpox. The drug tecovirimat (TPOXX) was approved in 2018 for the treatment of smallpox should someone show symptoms of the virus. The drug cidofovir has also worked well in early studies. Getting the vaccine within 3 to 4 days of contact with the virus may make the disease less severe or may help prevent it.

Beyond that, medical care aims to ease symptoms like fever and body aches, and control any other illnesses that a person can get when their immune system is weak. Antibiotics can help if someone gets a bacterial infection while they have smallpox.

Smallpox Complications

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If people got hemorrhagic or malignant smallpox, they would be more likely to die. The more fatal forms of the disease are more likely to affect women who are pregnant and people whose immune systems are impaired.

People who survive smallpox may be scarred on the face and body. In rare cases, they may become blind. Smallpox may also cause infertility in men, and it may cause miscarriage or stillbirths in women.

Smallpox Vaccine

Scientists use the cousin virus to variola -- the vaccinia virus -- to make the smallpox vaccine, because it poses fewer health risks. The vaccine prompts the body's immune system to make the tools, called antibodies, it needs to protect against the variola virus and help prevent smallpox disease.

No one knows for sure how long the smallpox vaccine protects people from the disease. Some experts believe it lasts for up to 5 years and wears off over time. Since it may not give lifelong protection, anyone vaccinated years ago as a child could be at risk of future infection by the variola virus. The only people known to be immune for life are those who have had smallpox and survived.

The World Health Organization and its member countries keep an emergency stockpile of the smallpox vaccine. It’s rarely used today, except for those few people who are around the variola virus, such as laboratory researchers working with variola and viruses like it.

Risks of the Smallpox Vaccine

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Some of its side effects can be dangerous, especially for people with weak immune systems. They can range from skin reactions to a serious nervous system condition called encephalitis, which can lead to convulsions, coma, and death. But these side effects are very rare. Based on historical data, for every 1 million people vaccinated for smallpox, one to two people died from a bad reaction.

Some people would have a higher risk of a reaction to the vaccine, like:

  • Women who are pregnant or breastfeeding
  • People with skin disorders such as eczema
  • People with a weak immune system due to a medical condition like leukemia or HIV
  • People on medical treatments, such as for cancer, that make the immune system weak

Smallpox as a Public Health Threat

It’s hard to know how major a threat a smallpox outbreak would be today. There are a few reasons that scientists can’t be sure:

  • The number of people around the world with weakened immune systems is higher today than when smallpox existed.
  • Countries used vaccines of different strengths during the global effort to end smallpox.
  • There’s no way to know for sure how long these different vaccinations give immunity to the virus.

If an outbreak of smallpox were to happen, public health measures would likely include these steps: find and vaccinate infected people, vaccinate health care workers and others at risk of infection, isolate smallpox patients to keep them from spreading the disease, and give vaccinations for the public as needed to contain the outbreak.

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