You really don’t need to know how to tell them apart. That’s because no one in the U.S. has had smallpox for more than 65 years. But there are still important things to know about both.
1. Chickenpox is still around. Smallpox is pretty much extinct.
Until recently, chickenpox was a very common illness, especially in kids. It made about 4 million people sick every year and sent more than 10,000 to the hospital. The chickenpox vaccine has made it much rarer. But people still catch it every year.
On the other hand, your odds of getting smallpox are close to zero. Thanks to the smallpox vaccine, this disease is all but gone. The last case anywhere in the world was in 1978. The only known samples of smallpox are in two secure research labs -- one in the U.S. and one in Russia.
2. Chickenpox is usually mild. Smallpox was often deadly.
The varicella virus causes chickenpox. It’s very easy to catch. If you have chickenpox, you'll get itchy blisters on the body (which eventually scab over), along with other symptoms like fever and tiredness. It usually lasts about 5 to 7 days.
Smallpox was very different. It was also caused by a virus (variola). It caused a rash, blisters, and fever, just like chickenpox. But it was much more serious. About 3 out of 10 people who got it died. Some who survived ended up blind or with permanent scars. Experts think that in the 20th century, it killed more than 300 million people.
3. Doctors can tell chickenpox and smallpox apart.
While they may look similar to the untrained eye, smallpox rashes are different:
Chickenpox sores show up at different times in different areas. They’re mostly on the stomach, chest, and back, and rarely on the palms or the soles of your feet.
Smallpox sores appeared all over the body at the same time (mostly on the face, arms, and legs, and sometimes on the palms and soles) and all looked the same.
4. Kids (and some adults) need the chickenpox vaccine. Almost no one needs the smallpox vaccine.
While chickenpox is a mild disease for most, it can sometimes cause dangerous problems -- especially in babies, adults, and people with weak immune systems. That’s why doctors recommend that all kids get the vaccine -- once around age 1, and a booster shot between ages 4 and 6. Older kids and some adults who never got the vaccine or chickenpox itself need it, too. It’s safe and up to 98% effective.
While there’s still a smallpox vaccine, people don’t need it anymore because there’s no one to catch smallpox from. In the United States, most people born after 1972 never got the vaccine. The only folks who might still get the shot are researchers in labs who work with smallpox (or similar viruses) and some members of the military.
5. Some experts worry that smallpox could be used as a weapon.
You may see news stories about smallpox from time to time. They’re usually about the possibility that a person or group could use the virus to make people sick.
It’s a scary thought. But it’s never happened, and it would be very hard to pull off. It is spread via direct contact with an infected person who has the classic rash and is coughing or sneezing (shedding respiratory droplets. It isn't spread through the air.
Remember that the only known samples are safe in two secure labs. But just in case of a disaster, the government keeps enough smallpox vaccine to protect every person in the United States and recently the drug tecovirimat (TPOXX) was approved to treat anyone who may contract the virus.