In 1952 there were 21,000 cases of paralytic polio in the US. It was one of the most feared diseases of the 20th century. Today, there are none. Although it had a rocky start, the polio vaccine is one of medicine’s greatest success stories.

Key Facts

  • Like small pox, polio is one of the few diseases that have the potential for global eradication. Hopefully within the next decade.
  • Only the inactivated polio vaccine (IPV) is used in the US. This vaccine does not cause polio or spread polio.
  • 95% of people with polio have no symptoms, which makes it easy to spread unknowingly.

What is polio?

Polio is a highly infectious illness which spreads through contact between people, by nasal and oral secretions and by contact with contaminated feces. The virus enters the body through the mouth, multiplying along the way to the digestive tract, where it continues to multiply and is excreted from the body.

While polio can infect people at any age it primarily affects children under 5. Cases of polio tend to peak in summer months. In more tropical climates there is no seasonal pattern.

Ironically, improvements in sanitation and clean water actually resulted in large polio epidemics prior to the vaccine. (Contrary to what you might hear or read about improvements in sanitation reducing all infectious diseases.) Why did this happen? With less exposure to natural or wild polio there was a greater number of people without immunity and at risk for the disease. (Who knew?)

The last case of endemic polio (wild virus) in the US was in 1979. A few cases after that were imported from other countries, but the majority of cases (144 out of 152) from the years 1980 to 1999 were vaccine-associated paralytic polio (VAPP). These cases were all caused by the live oral polio vaccine. Since 2000 it has been recommended that only the IPV (inactivated polio) vaccine be used.

There is no cure for polio. It can only be prevented.

The Vaccine

The first polio vaccine was available in 1955 (testing began in 1952, widespread availability in 1955) by Jonas Salk and was an inactivated polio vaccine (IPV). In 1961 the oral polio vaccine (OPV) was introduced by Albert Sabin. There was quite a bitter rivalry between these gentlemen. Development of Salk’s IPV was primarily in the US while Sabin’s OPV was tested outside of the US. OPV would prove to be the better vaccine for eliminating polio, but IPV is now used for individual protection.

Side Effects

Some people will be sore at the injection site. There are no known serious side effects from the vaccine. A vaccine, like any medicine, could cause serious problems, such as a severe allergic reaction. The risk of a polio vaccine causing serious harm is extremely small.

Why are some industrialized countries using a different vaccine for polio than developing countries? 

“Every country in the world except two (Sweden and Iceland) used oral polio vaccine (OPV) to eliminate polio and continued using OPV, usually until the late 1990s, when some switched to inactivated polio vaccine due to progress towards polio eradication (when the risk of wild poliovirus was diminished). Most countries use OPV as it has a unique ability to induce intestinal, local immunity, meaning that it can actually interrupt wild poliovirus transmission in an environment. This is not possible with IPV, an inactivated polio vaccine, which induces only very low levels of immunity to poliovirus inside the gut, and as a result provides individual protection against polio, but unlike OPV, cannot prevent the spread of wild poliovirus.” –Global Polio Eradication Initiative

Polio still flares up in developing countries, but there are only 3 countries where it is still endemic or common. IPV requires very fragile handling in a temperature-controlled environment and requires an injection, whereas OPV is more stable and is given by mouth. This makes it ideal for dissemination to large populations in remote regions where refrigeration is not possible.

IMPORTANT NOTE: The live attenuated virus vaccine (OPV) is no longer routinely used in the US or other developed countries. When you read or hear people say “the vaccine gives you polio,” you now know this information is incorrect; the source is uninformed and should not be trusted.

Common Misconceptions

Polio is no longer present in the US and so we don’t need to vaccinate for it.

Given that polio is still present in parts of the world and a high percentage of people have no symptoms, polio is still a threat. If we stopped vaccinating, chances are high that it would come back and the goal of eradication would be set back again.

Have Host, Will Travel!

“Polio does not respect borders—any unimmunized child is at risk. For every case of paralysis there are between 200 and 1000 children infected without symptoms. So, it is hard to detect polio and hard to prevent the virus from traveling. Children living in areas where immunity levels are low are particularly vulnerable. The best defense against polio importations is to eradicate the virus. Only then will all children be safe.” –Global Polio Eradication Initiative


The polio vaccine causes polio.

Yes, that did happen to some people, but not anymore. The last case of US endemic polio (wild virus) was in 1979. A few cases after that were imported from other countries, but the majority of cases (144 out of 152) during the year’s between 1980 and 1999 were vaccine-associated paralytic polio (VAPP). These cases were all caused by the live oral polio vaccine. Since 2000 it has been recommended that only the IPV (inactivated polio) vaccine be used which cannot transmit polio. However, there have been a few cases of VAPP imported from other countries.

The Cutter Incident

One of the worst pharmaceutical disasters in the US occurred shortly after mass vaccination against polio began in 1955. Cutter Laboratories in Berkeley, CA, produced 120,000 doses of the polio vaccine that contained live virus. The vaccine lots were quickly pulled from use, but at least 160 children were permanently paralyzed, 10 died and perhaps 40,000 experienced less serious bouts with the virus.

Polio in the World

Polio remains endemic in Afghanistan, Nigeria and Pakistan. Polio vaccination programs were halted in northern Nigeria in 2003 due to messages from political and religious leaders. These leaders argued that the vaccine could be contaminated with anti-fertility agents, HIV and cancerous agents. The goal of global eradication was set back more than a decade. Although the politicians eventually reversed themselves, the damage was done, and today the disease is spreading to neighboring countries such as Chad where it had been previously eliminated.

Bringing It Home

The risk of getting polio in the US is pretty slim. But then again the risk of an adverse event from the vaccine is probably slimmer. However, cases of polio still pop up in developed and undeveloped countries. Just this year a strain of polio was found in an Israeli sewer. Somalia has recently (2013) seen a very large outbreak of polio with the first case actually originating in Kenya. You might say, “I’d never go to Somalia.” But Somalia may come to you. Volunteers from Oregon go to Africa all the time and come back. Some of them may be unvaccinated. What if one of those unvaccinated volunteers unwittingly brought polio back to our community? Remember, most people who have polio have no symptoms but can still spread the disease.

Evaluating risk is very difficult in a situation like this. The chance of catching the disease seems too distant, the risk too small. However, we urge you to vaccinate and be a part of something bigger, something global. Be a part of eradicating polio and ending the need for the vaccine.

Just for Fun!!

On the History of Vaccines website you can find a fun page. It is recollections of the children who participated in the largest ever vaccine trial.


CDC, Pink Book

Children’s Hospital of Philadelphia, History of Vaccines

Global Polio Eradication Initiative