What Is Polio?
Key takeaways:
Polio is a viral illness that spreads from person to person in contaminated food and water.
In the U.S., a polio epidemic in the early twentieth century left thousands of children dead or permanently disabled. A series of vaccines finally brought the epidemic to an end.
Today, polio is nearly gone from most parts of the world. Officials are hopeful that a strong vaccination effort will eliminate it everywhere.
While most people have heard about polio, it doesn’t usually cause much concern these days. That’s an enormous change from 70 years ago. At that time polio ran rampant through large parts of the world — including the U.S. — and left thousands of children dead or permanently paralyzed.
What is it like to catch polio? And could polio ever become an epidemic again? Living through the COVID-19 pandemic has given all of us a new perspective on what it’s like to have a deadly illness spreading through our communities. Can 70 years of scientific advancement and vaccine development protect us from having to face polio again in the future?
What are the symptoms of polio?
Polio starts out as an infection of the gut. The virus enters the body through the mouth, and it multiplies in the throat, stomach, and intestines.
Most people — 3 of every 4 who catch polio — never have symptoms during this early stage. When polio does cause symptoms, it most often feels like the flu, with symptoms like:
Fever
Headache
Sore throat
Upset stomach
Fatigue
For a smaller number of people — approximately 1 out of every 150 infected people — polio moves from the gut to the bloodstream and affects the brain and nervous system. This causes neurologic symptoms that include:
Meningitis, or inflammation around the brain
Paresthesias, or an uncomfortable tingling feeling in the legs
Paralysis, or severe muscle weakness
These symptoms can be permanent or life-threatening. Some people get better, but then decades later develop post-polio syndrome — with crippling weakness and fatigue.
How does polio spread?
Polio is caused by a virus in the enterovirus family. Like other enteroviruses, polio spreads from person to person in body fluids. Most often it spreads in feces and sewer waste. It can also spread in saliva or spit.
Before there was a vaccine, polio was common during the summer months. Many scientists believe that warm, humid air helps polio spread. Even today, polio is most difficult to fight in parts of the world that stay warm year-round.
Who gets polio?
Most often polio is a disease of young children. It is sometimes called “infantile paralysis,” because it frequently affects infants. That said, it can affect people of any age.
Polio spreads quickly in communities with poor sanitation. In these places, children are often exposed to polio from sewage when they are very young (before their first birthday). Children who live in places with better sanitation are more likely to be older when they are first exposed to polio.
People who catch polio develop immunity, which keeps them from catching it again.
What happened during the polio epidemic?
Although polio has been around for centuries, the number of people catching it remained low for a long time.
In the twentieth century, cases of polio in the U.S. and other developed countries started to rise. By the 1950s, polio was infecting tens of thousands of children every summer. Thousands of children became paralyzed, and many died.
People in the 1950s were very frightened of polio. Since polio always hit in the summer, some people thought that insects spread polio. This turned out to be wrong. But since most people who caught polio never showed symptoms, it was hard to predict who was going to get sick next. And no one knew how to keep polio from paralyzing their children.
What is an ‘iron lung’?
The most dangerous thing about being paralyzed from polio was not being able to breathe. Normally, our chest and diaphragm muscles work to pull air into our lungs. But breathing is difficult when polio weakens those muscles.
The “iron lung” is a device that helps pull air into the lungs. It looks like a large metal tube that completely surrounds a person who lies down on a cot. At one end, the person’s head sticks out. At the other end, a set of bellows forces air in and out of the tube. As air pressure in the tube drops, the rib cage is pulled outward, and air flows in through the person’s mouth and nose. When the air pressure inside the tube climbs, the chest is squeezed and air is pushed back out.
During the polio epidemic of the early 1950s, thousands of children spent weeks or months lying inside iron lungs. Some of those children eventually recovered enough to breathe on their own. Others continued to need an iron lung, and then later on needed ventilators for the rest of their lives.
How did the polio epidemic end?
Cases of polio continued to surge every summer until a vaccine was developed.
Dr. Jonas Salk created the first polio vaccine in the early 1950s. It was called the IPV, or inactivated poliovirus vaccine. It was given to children as an injection, and it was very effective at preventing paralysis from polio.
Several years later Dr. Albert Sabin developed a new vaccine against polio. The OPV — or oral poliovirus vaccine — could be taken by mouth, which made it easier to give than the IPV. The OPV was tested in the Soviet Union during the 1950s and approved for use in the U.S. in 1960.
How does the polio vaccine work?
All vaccines work by strengthening the immune system. They do this by teaching the immune system what a virus that causes disease looks like. Since the immune system has a memory, this prepares the immune system to respond quickly if it ever encounters that virus again.
Oral vs. injectable polio vaccines
Both the OPV and the IPV are important tools in the fight against polio.
The IPV is the polio vaccine given in the U.S.
Since 2000, the IPV has been the only polio vaccine used in the U.S. It is very effective at keeping polio from spreading through the bloodstream, so it prevents polio’s neurologic symptoms — paralysis and death.
Unfortunately, the IPV doesn’t stop the passage of polio through the gut. If a person immunized with IPV catches polio, the virus could still multiply in their stomach or intestines — and it could still spread to others.
The OPV plays an important role in stopping the spread of polio
The OPV contains a live, weakened version of the polio virus. This vaccine-virus can multiply inside the gut and produce immunity, but it doesn’t cause symptoms. The result is immunity inside the stomach and intestines as well as in the bloodstream.
But the OPV has a downside. While the vaccine version of polio is not dangerous, it is contagious. Occasionally it can pass between people and, every once in a while, it can mutate into a strain that causes full-blown polio disease. For this reason, it isn’t used any more in the U.S. or other places that have very low rates of polio.
Can I get a polio vaccine for myself or my child?
In the U.S., all children are recommended to get 4 doses of the IPV. According to the standard vaccine schedule, children should get IPV when they are:
2 months old
4 months old
Between 6 and 18 months old
Between 4 and 6 years old
Vaccination against polio has been part of the childhood immunization schedule since the mid-1960s.
Adults who have never been vaccinated against polio can be immunized with a series of 3 doses of the IPV. This is especially important for adults who are:
Traveling to a part of the world where polio is still present
Working in a healthcare setting and could be exposed to a patient with polio
Working in a lab that handles polio virus for research or testing
Is polio still around?
Wide-reaching vaccination efforts have been very effective at defeating polio around the world. Here are some key facts:
There haven’t been any cases of polio in the U.S. since 1979.
Brazil had a case in 1991 — that was the last case in the Americas.
In 2002, there was a case in Turkey — that was the last case in Europe.
Africa was declared free from polio in 2020.
That left only two countries — Afghanistan and Pakistan — with naturally-occurring polio. Unfortunately, political conflicts and the COVID-19 pandemic have made delivery of vaccines to these countries very difficult.
Could polio come back?
Polio as we used to know it still exists. It still spreads easily and causes devastating disease. We still do not have a cure.
Better polio vaccines are still being developed. In 2020 the World Health Organization approved a new type of polio vaccine — with a live virus that is much less likely to mutate.
Right now the reason we don’t worry much about polio is because nearly everyone in the U.S. has been vaccinated. The vaccines work well, and most people have received the recommended doses. But if we don’t keep up our vaccine efforts, polio could become a problem for us again.
The bottom line
Polio is an ancient disease caused by a virus that spreads easily from person to person. Although it doesn’t usually cause symptoms, it can result in severe disability or death for some people — and in many cases, those people are children.
In the mid-twentieth century, polio spread widely in the U.S. It took a new vaccine — and a massive vaccination effort — to get polio under control.
These days polio is rare, but it could come back if we allow it to. Modern diagnostic and vaccine technology, public health surveillance, and international cooperation are our best defenses against polio becoming a problem again.
Why trust our experts?
References
American Academy of Pediatrics. (2021). Polio vaccine: What you need to know.
Bigouette, J. P., et al. (2021). Progress toward polio eradication — worldwide, January 2019–June 2021. CDC: Morbidity & Mortality Weekly Report.
Centers for Disease Control and Prevention. (2021). Polio vaccination.
Centers for Disease Control and Prevention. (2021). Polio vaccination: What everyone should know.
Centers for Disease Control and Prevention. (2021). Post-polio syndrome.
Centers for Disease Control and Prevention. (2021). What is polio?
Chumakov, K., et al. (2021). Polio eradication at the crossroads. The Lancet.
Guglielmi, G. (2020). Africa declared free from wild polio - but vaccine-derived strains remain. Nature.
Janssen, V. (2020). When polio triggered fear and panic among parents in the 1950s. The History Channel.
Nathanson, N. et al. (2010). From emergence to eradication: The epidemiology of poliomyelitis deconstructed. American Journal of Epidemiology.
Rotary International. (2021). What is polio?
The College of Physicians of Philadelphia. (2021). The history of vaccines: Timeline.
World Health Organization. (2020). First ever vaccine listed under WHO emergency use.
