Polio 101: What it is, how it spreads and how to know if you've been vaccinated

Published August 31, 2022


A recent New York case of paralytic polio in an unvaccinated person has brought attention to a disease we don't often hear about anymore. Here we will explore polio, how it spreads and what you need to know about vaccination.  

What is polio?

Polio, or poliomyelitis, is a disease caused by the poliovirus. The poliovirus can impact people in various ways. While some people may not have visible symptoms or even know they're carrying the virus, others may have flu-like symptoms. In rarer cases, people can develop disabling and potentially life-threatening symptoms affecting the brain and spinal cord, causing meningitis or paralysis. 

"About one in 500 people infected with poliovirus will develop paralysis – that is why this one case in New York is only the tip of the iceberg," says Mark Rupp, MD, Nebraska Medicine infectious diseases specialist. Undoubtedly, there are many others who have been infected but were asymptomatic or only mildly ill. This is supported by the finding of poliovirus in wastewater 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 to breathe. Further, children who seem to recover fully can develop post-polio syndrome as adults, which brings on new muscle pain, weakness or paralysis decades later.

Polio vaccines – a look back

Although polio wasn't new, outbreaks in the U.S. skyrocketed in the late 1940s, disabling an average of over 35,000 people yearly. Franklin Roosevelt is probably the best-known case of polio in the U.S., having contracted polio at age 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 fewer than 10 in the 1970s. 

It's no coincidence that wild poliovirus has been eliminated in the U.S. for more than 30 years.

After the peak of the outbreak in 1952, dedicated health care professionals, adults, and parents making sure their children were vaccinated played a significant role in its eradication. No polio cases caused by wild poliovirus have originated in the U.S. since 1979. However, a few cases have been brought into the country by travelers with polio. 

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

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

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

"This is why we need to ensure everyone is protected from polio through vaccination and get into those last places of the world where the wild poliovirus still exists," says Dr. Rupp. "We can put polio into the history books by realizing that vaccine-preventable diseases are not gone. They are simply kept at bay through vaccinations and can come back if we let down our guard. Low vaccination rates keep the door open to spreading the disease."

How does polio spread?

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

  • The poliovirus can live in an infected person for quite some 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 pass 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 right now," says Dr. Rupp. "People can transmit the virus without knowing it, and unvaccinated people can be infected and develop paralysis. We probably don't need to be worried about a large outbreak, but it becomes very worrisome when we have large populations of unvaccinated people. In some zip codes in the NYC area, the polio vaccination rate in children is as low as 37%. The national average polio vaccination rate in 2-year olds in the United States is 93%." 

People most at risk of infection include:

  • Unvaccinated people
  • People who never received all the recommended vaccine doses
  • People traveling to areas that may put them at risk of infection 
  • People who work in a lab or health care setting that handle specimens, treat patients who may have polio, or come in close contact with an infected patient

How do I know if I've been vaccinated?

If you're an adult that attended a U.S. public school, more than likely, you were vaccinated in childhood. But if you're unsure or can't remember, there are several ways to find out:

  • Hunt down your school immunization records
  • Ask your parents or caregivers
  • Request your vaccination records from your primary care doctor
  • Previous employers may have a record of required immunizations
  • Request records from the health department of the state you were most likely vaccinated

Polio vaccine recommendations

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


  • The CDC recommends that children get four doses of polio vaccine – one dose at each of the following ages: 2 months old, 4 months old, 6 through 18 months old, and 4 through 6 years old 
  • Children who have not started their polio vaccine series or who are delayed in getting all recommended doses should begin as soon as possible or finish their series by following the recommended catch-up schedule


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

  • Adults who completed their polio vaccination but who are at increased risk of coming in contact with poliovirus may receive one lifetime IPV booster
  • Adults who are unvaccinated or without any documentation of previous polio vaccination should be given three doses of IPV at the recommended intervals
  • Adults who are incompletely vaccinated or previously received one or two doses of polio vaccine (IPV or OPV) should receive the remaining doses of IPV. Talk to your doctor about recommended intervals to complete the three-dose series
  • When there is not enough time to give three doses of IPV according to the recommended intervals, talk to your doctor about an accelerated schedule


Check the CDC's Vaccination for international travelers resource if you plan to travel.