1950s photo of children with polio inside iron containers.

Is Polio Making a Comeback?

In July, the New York State Department of Health reported a case of polio in Rockland County, a New York City suburb, and wastewater samples reveal the virus has been circulating in New York City and its suburbs for months.

More than 90% of Americans have been immunized against polio, but the news is still unsettling and has many wondering if they’re at risk of becoming infected or even paralyzed.

We spoke with Vincent Racaniello, PhD, a poliovirus expert at Columbia University Vagelos College of Physicians and Surgeons, to get answers to the public’s most common questions and what the presence of the virus means for public health. Racaniello has been studying the poliovirus since the 1980s and is the host of This Week in Virology, a podcast created by Racaniello and Columbia microbiologist Dickson Despommier, PhD, in 2008.

How did the man in Rockland County get polio?

He had traveled to Europe before getting sick, but the particular strain he was infected with has not been found in any of the places he visited. That means he was infected here in the United States.

Poliovirus is acquired by what we call fecal-oral contamination. This is not a virus that is transmitted through the air like influenza or the virus that causes COVID. Poliovirus reproduces in the intestines and is shed in the feces. Anyone who comes into contact with contaminated fecal material or wastewater is at risk of getting with the virus. So you could get it after shaking hands with someone who’s just been to the bathroom and didn’t wash their hands very well.

The Rockland patient was not vaccinated against polio. That would not have stopped him from getting infected with the virus, but he would not have experienced any symptoms.

The Americas were declared polio-free in 1994. How could this happen?

To answer that, you have to understand the two types of polio vaccines. There’s an injectable polio vaccine that contains an inactivated poliovirus and an oral polio vaccine that contains a weakened poliovirus that cannot cause polio.

Since the oral vaccine is inexpensive and easy to administer, it has been the preferred vaccine in many countries. The downside is that the weakened virus in the oral vaccine reproduces in the intestines and is shed into feces. In most vaccine recipients, the weakened virus in the vaccine can mutate and once again become dangerous. Only very rarely—one in 1.4 million doses given to kids—does that cause polio in the recipient. But if the community immunization rate is below 90%, these vaccine-derived strains circulate extensively, and you’re going to have an outbreak.

So what’s happened here is that the weakened virus has reverted in someone who’s been vaccinated with the oral vaccine, and that vaccine-derived virus is spreading.


This is why the United States stopped using the oral vaccine in 2000 and switched to the injectable vaccine. The inactivated virus in the injectable vaccine cannot reproduce inside you and so it cannot mutate and cause disease.

Both types of vaccine are very effective at preventing the virus from getting into your nervous system where it can cause paralysis, but neither vaccine will prevent you from getting infected. That means vaccinated people can catch and spread poliovirus without knowing it.

Are you alarmed by this one case?

No, not at all. This case occurred because he lives in a community that is under-immunized and he wasn’t vaccinated. With a few exceptions—including some New York City neighborhoods—the rest of the country is well-immunized and will be protected against paralytic disease.

But this is a wake-up call. People have become complacent about polio. They think that it’s been eradicated. It hasn’t. The virus has been detected in wastewater in Rockland and in New York City, which means it’s circulating among the general public. And as a consequence, we have a case of polio, and I would not be surprised if we saw more cases in the coming weeks.

Poliovirus probably circulates in many other places in the United States as well. We just haven’t been testing for it.

Because of global travel, the virus can spread anywhere. So we have to remain vigilant about immunization.

Many people were vaccinated decades ago. How long does the protection last?

The vaccine is very durable. As far as we know, it should last a lifetime.

If you’re unsure of your status, get vaccinated. It’s safe even if you’ve had previous doses of the vaccine. The vaccine is usually covered by insurance and is widely available.

Three doses are needed for full protection against polio. If you don’t know if you received all three doses, you should receive additional doses of inactivated vaccine. If you previously received the oral poliovirus vaccine you can still receive the inactivated vaccine.

Does anyone need a polio booster shot?

People with immune deficiencies—transplant recipients or patients receiving drugs to treat conditions such as rheumatoid arthritis or inflammatory bowel disease—may need to get boosted. Also, anyone who’s planning to travel to a country with there’s a lot of polio should get boosted.

man examines leg of child lying down on a table

This historic image depicts a CDC officer determining if a young girl had experienced any paralytic effects as a result of a poliovirus infection. Among unvaccinated people, most cases of polio are asymptomatic. About a quarter have mild flu-like symptoms for a week or so. A small percent experience a brain infection called meningitis but will fully recover. Less than 1% have muscle weakness or paralysis in the arms or legs, usually on one side of the body. The virus can also affect the muscles that support breathing, which is why iron lungs were used in the 1950s and 60s. Photo: CDC.

Aside from getting vaccinated, what else can one do to prevent infection?

Wash your hands with soap and water after using the restroom and before touching your mouth or eating. This activity will help prevent fecal-oral contamination.

Hand sanitizer doesn’t inactivate poliovirus.

Will polio ever be eradicated?

There’s a chance that we could eliminate wildtype, or naturally occurring, poliovirus, which at present exists in only two countries, Pakistan and Afghanistan. However, as long as we continue to use the oral vaccine, the virus will continue to circulate and some unvaccinated people will get so-called vaccine-derived polio. We've essentially replaced wild polio viruses with vaccine-derived polio viruses.

The World Health Organization, which underwrites the Polio Global Eradication Initiative, has commissioned the development of a new oral vaccine that won’t cause vaccine-derived polio. But even if a better oral vaccine is developed, it will take many years for that vaccine to be put into widespread use.



More information

"A Brief History of Poliomyelitis" | Columbia University lecture by Vincent Racaniello

Vincent Racaniello, PhD, is the Higgins Professor of Microbiology & Immunology at Columbia University Vagelos College of Physicians and Surgeons.