So, how worried should I be about polio?

As if COVID and monkeypox weren’t enough, the unfortunate plague news keeps on coming: Polio is back. The virus-caused disease, which the United States hasn’t had a case of in nearly 20 years, has been detected recently in multiple New York counties, as well as the U.K. and Israel.

“There is currently a simultaneous, new polio epidemic in the U.K. and the United States,” William Haseltine, PhD, author of My Lifelong Fight Against Disease: From Polio and AIDS to COVID-19 and former Harvard Medical School professor, tells Mic. So far this summer, officials in the U.S. have found the virus in wastewater systems in New York State’s Rockland and Orange Counties, and New York City. As of now, only one person has tested positive for the virus — a young, unvaccinated adult in Rockland County who is now paralyzed as a result of the disease — though health officials suspect there are many more cases circulating.

“This is of concern because for every person paralyzed, a minimum of 200 people have been infected unknowingly — that is to say, without any serious symptoms other than perhaps a mild cold,” Haseltine says. “The detection of the virus in multiple sites and wastewater indicates that the virus is spreading in the population, especially in New York.”

So now that polio has returned, it’s time for us to get up to speed on the virus, how it affects us, and what we can do to prevent it.

What is polio?

Polio — short for poliomyelitis — is a virus that spreads through contaminated food, water, and respiratory droplets. It most often affects young children under the age of 5, but people of all ages are susceptible. The virus, which has been largely eradicated from most countries since 1979 thanks to vaccines, can cause flu-like symptoms for mild cases, or paralysis and death for more severe ones. It attacks the nervous system and spinal cord. There is no cure, but we do have incredibly effective vaccines.

According to the PATH Center for Vaccine Innovation and Access, two types of polio can be found in the world right now: WPV1 (wild poliovirus type 1) and cVDPV2 (circulating vaccine-derived poliovirus type 2). It’s an important distinction. WPV1 is the most commonly known, but not the most common — at least not anymore. WPV1, the naturally occurring virus, is endemic to only two countries, Afghanistan and Pakistan. People could bring it to other countries if they caught the virus while traveling. Florida-based infectious disease specialist Ramprasad Gopalan, MD notes that no wild poliovirus has originated in the United States since 1979.

Why is polio spreading again?

It’s not known exactly how polio made its way back into the U.S., but we do know that the current outbreak, both in the U.S. and the U.K., is specifically of vaccine-derived polio, or cVDPV2. This is “a vaccine-associated virus, when the oral polio vaccine (OPV) — which has a weak virus that usually doesn't cause disease — mutates and causes disease then spreads to others,” Gopalan said.

As NPR reported, western countries most often use a polio vaccine containing the inactivated virus (IPV), which doesn’t allow for any possibility of further spread of the disease. But in some lower-income countries, residents receive a (more affordable and easier to distribute) oral live vaccine, which gives people immunity by exposing them to the weakened virus. That same virus can then spread into sewage systems via peoples’ stool; in many cases, unvaccinated people exposed to the wastewater gain immunity — but sometimes that weakened virus can mutate, spread, and regain its ability to infect people.

Per the New York State Department of Health, experts believe the current outbreak originated with someone who received OPV outside of the U.S. and spread to people — including the first patient with a confirmed case — who were unvaccinated. And therein lies the issue: As vaccination rates in the U.S. decrease (which they have, especially during the COVID pandemic, as the Los Angeles Times reported), diseases like polio have a greater opportunity to spread. It’s not a coincidence that the areas where the virus is popping up have relatively low vaccination rates.

“The anti-vaccine movement has dissuaded many people for a number of years from vaccinating their children,” Haseltine says. “[Due to] the success of the anti-vaccine movement, we see large portions of the population, especially those 30 and younger, at risk.”

Should I be concerned about getting polio?

The absolute best thing you can do to protect yourself is to get vaccinated if you aren’t already. If you are vaccinated against polio — most adults who grew up in the U.S. are, as it’s a requirement for child care and schools — you don’t need to be too worried. That said, it’s worth double checking that you are and that you’ve received the full series. Per the CDC, two doses of the IPV jab offer 90% protection against polio, and three doses gets you to at least 99% protection. If you haven’t been vaccinated or only received one or two doses, it’s time to contact your doctor or local health department and set up that appointment.

The IPV has been the sole polio vaccine distributed in the U.S. since 2000, but if you’re in a country without access to that one, it’s still worth getting the oral polio vaccine. Both of them protect against infection, transmission, and paralysis.

Do I need a polio booster shot?

The CDC is recommending single, lifetime polio vaccine boosters for certain groups of people who are particularly high-risk for contracting the virus. That includes people traveling to countries with higher risk of transmission, people working in labs or healthcare settings who handle specimens containing the virus, and people (including healthcare workers) who treat or have close contact with polio patients. If you think you may qualify for a polio booster, give your doctor a call.

“The anti-vaccine movement has dissuaded many people for a number of years from vaccinating their children,” Haseltine says, noting that the U.S. vaccination rate ranges from less than half to more than 90%, depending on where you are. “[Due to] the success of the anti-vaccine movement, we see large portions of the population, especially those 30 and younger, at risk.”

Can I still travel?

A polio outbreak should not stop you from traveling. As long as you take all the precautions — getting fully vaccinated or getting a booster if you need one, and staying away from contaminated water — you should be perfectly fine. If you’re going to be in close contact with people who are coughing or sneezing, consider wearing a mask.

Could this become another pandemic?

According to Haseltine, we’re already at epidemic level — meaning a large number of cases have broken out in a community. To reach pandemic levels, it would have to be widespread around the world. And, unfortunately, that is a possibility. “In the United States, we can expect continued unchecked spread of the virus as a result of vaccine reticence in large segments of the population,” Haseltine said. “This is likely to result in a nationwide spread of infectious poliovirus and many additional cases of paralysis, particularly in those under 30 and in other countries and regions with low polio vaccination rates. This unfortunate situation was entirely avoidable if populations had adhered to recommended childhood vaccine policies.”