Is Polio Back? Here's What You Need to Know

Polio was one of the most feared viruses in the 1940s and 1950s. Outbreaks caused more than 15,000 cases of paralysis each year until vaccines were introduced beginning in 1955. Thanks to the polio vaccine and vigilant public health efforts encouraging people to fully vaccinate their children, wild (naturally spread) poliovirus has been eliminated from the United States for more than 30 years.

But in June 2022, an unvaccinated Rockland County, New York, man in his 20s was diagnosed with vaccine-derived poliovirus. A month later, the New York State Department of Health caught wind of this and launched a wastewater surveillance. The Centers for Disease Control and Prevention (CDC) analyzed the samples and confirmed that poliovirus — specifically the type that can cause paralysis in humans — was found in samples collected from Rockland County and three other counties, plus New York City.

New York Gov. Kathy Hochul issued an executive order declaring a state of emergency Sept. 9, 2022, and urged those who were not fully vaccinated against polio to get vaccinated immediately. The World Health Organization also added New York to the list of places in the world where vaccine-derived polio is actively spreading.

Is polio making a comeback in the United States and, if so, are we at risk?

"At this moment, the most important thing is to confirm you are vaccinated [against polio]. Everybody in the United States was vaccinated unless you know of a reason why you may not have been," says Howard Forman, M.D., professor of radiology and biomedical imaging, public health/public policy, management and economics at Yale University. "If you haven't been vaccinated, you should get vaccinated. And if you're unsure of your vaccination status and can't confirm through your own medical records, you can still get vaccinated."

Poliovirus is very contagious. It is spread through person-to-person contact via the stool of an infected person or the droplets of a sneeze or cough. Most people who contract poliovirus have no symptoms. About a quarter of them have mild, flu-like symptoms such as fever, diarrhea, upset stomach and body aches. Most people may not be aware they have polio.

But about 1 in 200 to 1 in 1,000 people who become infected will develop a paralytic version of the disease known as poliomyelitis. Poliomyelitis can range in severity from mild disability to acute respiratory failure and death. People who have been vaccinated against the virus have almost no chance of getting paralytic polio, Dr. Forman reassures.

Despite public health efforts to vaccinate all children against polio, some people in the U.S. may not have received the oral or injectable vaccine or gotten a full four-shot protocol. Those individuals are at risk of contracting polio. This includes young children.

The only polio vaccine currently approved by the U.S. Food and Drug Administration (FDA) is the inactivated polio vaccine (IPV). It is given by shot in the arm or leg, depending on the person's age. The CDC recommends that children get four doses at 2 months, 4 months, 6-18 months, and 4-6 years.

Wild (naturally occurring) polio virus is the most commonly known form of poliovirus. However, another form of the disease that can spread among communities is called circulating vaccine-derived poliovirus, or cVDPV. While rare, cVDPV has been increasing in recent years in communities with low immunization rates. It's the only form of poliovirus we've seen in the U.S. in recent decades. And yes, it's the same form of polio that was recently found in New York.

There have been two vaccines widely used to prevent polio — the injectable inactivated poliovirus (IPC) and the oral polio vaccine (OPV).

The oral vaccine is a live attenuated (weakened) vaccine virus that provides better immunity in the gut, where polio replicates. The virus is also excreted in the stool and is how researchers are able to detect it in sewer samples. This also means that it can still spread from person-to-person. If you're vaccinated, it's not a concern.

But in communities with low immunization rates, the virus can spread from one unvaccinated person to another. Over a period of about 12 to 18 months, it can mutate much like the wild poliovirus, and can lead to cases of paralytic polio.

While extremely effective, the oral vaccine does carry a very remote risk of causing paralytic polio. Because of this, in 2000, the U.S. stopped administering the oral vaccine altogether and only gives the inactivated poliovirus shot.

New York public health officials believe that the young Rockland County man who was diagnosed with paralytic polio last summer came in contact with someone visiting the U.S. from another country who had a vaccine-derived virus infection. And because he wasn't vaccinated, his body was otherwise defenseless against the virus.

According to the CDC, "Most adults in the United States were vaccinated as children and are therefore likely to be protected from getting polio. In general, unless there are specific reasons to believe they were not vaccinated, most adults who were born and raised in the United States can assume they were vaccinated for polio as children. Polio vaccination has been part of the routine childhood immunization schedule in the United States for decades and is still part of the routine childhood immunization schedule. Adults who received any childhood vaccines in the United States almost certainly were vaccinated for polio."

The important thing to note is that "these vaccines remain extremely safe," Dr. Forman says. "If you're vaccinated, you're safe. If you haven't been vaccinated, you still have time to get vaccinated."