Polio 101: what it is, how it is spread and how to know if you are vaccinated

photo of a baby being vaccinated

A recent case of paralytic poliomyelitis in New York in an unvaccinated person has drawn attention to a disease we no longer hear about often. Here we’ll explore polio, how it spreads, and what you need to know about vaccination.

What is polio?

Poliomyelitis, or poliomyelitis, is a disease caused by the poliovirus. Poliovirus can affect people in several ways. While some people may not have visible symptoms or even know that they are carrying the virus, others may have flu-like symptoms. In rarer cases, people can develop disabling and life-threatening symptoms that affect the brain and spinal cord, causing meningitis or paralysis.

“About one in 500 people infected with poliovirus will develop paralysis, which is why this case in New York is just the tip of the iceberg,” says Mark Rupp, MD, an infectious disease specialist at Nebraska Medicine. There are undoubtedly many others who have been infected but were asymptomatic or only mildly ill. This is supported by the finding of poliovirus in sewage surveillance in several New York counties.”

According to the Centers for Disease Control and Prevention, between 2 and 10 out of 100 people with paralysis from poliovirus infection die because the virus affects the muscles used for breathing. In addition, children who appear to fully recover can develop post-polio syndrome as adults, causing new muscle pain, weakness, or paralysis decades later.

Polio Vaccines: A Retrospective Look

Although polio was not new, outbreaks in the US spiked in the late 1940s, disabling an average of more than 35,000 people a year. Franklin Roosevelt is probably the best known polio case in the US, as he contracted polio at the age of 39 in 1921. The introduction of polio vaccines made a considerable difference. The first vaccine was introduced in 1955 (trivalent inactivated poliovirus vaccine or IPV), and the second in 1963 (trivalent oral poliovirus vaccine or OPV). Cases fell to less than 100 in the 1960s and less than 10 in the 1970s.

It is no accident that wild poliovirus has been eliminated in the US for more than 30 years.

After the outbreak peaked in 1952, health professionals, adults, and parents dedicated to making sure their children were vaccinated played a major role in eradicating it. No cases of polio caused by wild poliovirus have originated in the US since 1979. However, some cases have been brought to the country by travelers with polio.

The recent New York case was caused by type 2 vaccine-derived poliovirus (VDPV) in an unvaccinated person.

When allowed to circulate in underimmunized or unimmunized populations for long enough or to replicate in a person with a compromised immune system, this type of weakened virus can revert to a form that causes disease and possible paralysis. A small handful of these cases have been identified in the US since 2000. All were related to viruses in people who were not vaccinated or had weakened immune systems.

Although OPV is effective and has been instrumental in eliminating wild poliovirus worldwide, the US has used IPV exclusively since 2000 by injection to prevent vaccine-derived polio. IPV protects against paralytic disease caused by any type of poliovirus, including VDPV. The vaccine is more than 99% effective in preventing polio.

“That’s why we need to make sure everyone is protected against polio through vaccination and reach the last places in the world where wild poliovirus still exists,” says Dr Rupp. “We can put polio in the history books by realizing that vaccine-preventable diseases have not disappeared. They are simply kept at bay through vaccinations and can return if we let our guard down. Low vaccination rates hold the door open to the spread of disease.

How is polio spread?

Poliovirus is contagious and only infects people (spreads from person to person). Entering through the mouth, it is spread primarily through contact with the feces (poop) of an infected person, even in small amounts.

  • Poliovirus can live in an infected person for a long time
  • It can contaminate food and water in unsanitary conditions, such as in areas with poor access to health care or war-torn countries.
  • Infected people can still spread the virus to others and make them sick even if they don’t have symptoms.

“More people are getting this vaccine-derived strain, getting infected and shedding it than we know at this time,” says Dr. Rupp. “People can spread the virus without knowing it, and unvaccinated people can become infected and develop paralysis. We probably don’t need to worry about a large outbreak, but it becomes very concerning when we have large populations of unvaccinated people. In some zip codes in the New York area, the polio vaccination rate for children is as low as 37% The national average polio vaccination rate for 2-year-olds in the United States is 93%.

People at higher risk of infection include:

  • unvaccinated people
  • People who never received all the recommended doses of vaccines
  • People who travel to areas that may put them at risk of infection.
  • People who work in a laboratory or health care facility that handles samples, treats patients who may have polio, or comes into close contact with an infected patient.

How do I know if I have been vaccinated?

If you’re an adult who attended public school in the US, chances are you were vaccinated as a child. But if you’re not sure or can’t remember, there are several ways to find out:

  • Look up your school’s immunization records
  • Ask your parents or caregivers
  • Request your immunization records from your primary care physician
  • Previous employers may have a record of required vaccinations
  • Request records from the health department of the state in which you were likely vaccinated

Polio Vaccine Recommendations

Vaccination is a vital tool in reducing the risk of polio. There are no known risks of receiving IPV at the same time as other vaccines. If you have been fully vaccinated as a child, you are protected for life.


  • The CDC recommends that children receive four doses of polio vaccine: one dose at each of the following ages: 2 months, 4 months, 6 to 18 months, and 4 to 6 years.
  • Children who have not started their polio vaccine series or who are late in receiving all recommended doses should start as soon as possible or finish their series following the recommended catch-up schedule.


The recommended vaccination for adults will depend on previous polio vaccination records and the time available before protection is required.

  • Adults who have completed their polio vaccination but are at increased risk of coming into contact with poliovirus can receive a lifetime IPV booster.
  • Adults who are unvaccinated or without any documentation of prior polio vaccination should receive three doses of IPV at the recommended intervals.
  • Adults who are not fully vaccinated or who previously received one or two doses of polio vaccine (IPV or OPV) should receive the remaining doses of IPV. Talk to your doctor about the recommended intervals for completing the three-dose series.
  • When there isn’t enough time to give three IPV doses at the recommended intervals, talk to your doctor about an accelerated schedule


See the CDC’s Immunizations for International Travelers resource if you plan to travel.

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