Thanks to the invention of an effective vaccine, and the successful vaccine campaign that followed, the US (and much of the rest of the world) has been polio-free since 1979. So when a case of polio with paralysis was confirmed in an unvaccinated person from New York, alarm bells went off. New York declared a disaster to increase the vaccine reach, and health officials everywhere are reminding people to get their children vaccinated against polio, a vaccine-preventable disease.
On Tuesday, the US Centers for Disease Control and Prevention announced that the country is now one of 30 in the world that has vaccine-derived polio virus circulating in a limited area, following wastewater samples that detected polio in five counties in New York. While the oral polio vaccine, which uses a weakened but live virus, is no longer given out in the US, other countries still use it because it is a very fast and effective way to immunize communities against polio. But sometimes the weakened virus can change enough to become contagious, and in rare cases, cause severe disease in people who aren’t vaccinated.
In communities where the vast majority of people are vaccinated, this isn’t typically a problem, says Ross Kedl, immunologist and professor at the University of Colorado Anschutz School of Medicine. But in communities where vaccine rates are lower than normal – like Rockland County, where the polio case was reported – polio again becomes an issue.
“Where it does cause troubles is in communities where the vaccine uptake is lower than it needs to be,” Kedl said.
He added that polio is not a wide threat to the US right now – at least to those who were vaccinated against it. The majority of us were fully vaccinated as children, and it’s a requirement for attending most schools. What’s more, polio vaccination has largely avoided the politicization and misinformation campaigns of other vaccines, Kedl says, in part because the devastation, paralysis and death the disease caused in the 1940s is still somewhat fresh in people’s memories. And much of that harm was done to children.
“When you start targeting children, people sit up and take notice,” said Kedl.
Here’s what we know about polio vaccination, including how long immunity lasts and which few people need a polio booster right now.
What kinds of polio vaccines are there?
There are two types of polio vaccine. The injectable, inactivated vaccine is the only one that’s been given out in the US since 2000, and it’s recommended as a series of four shots typically given before age 6. The CDC recommends the first shot at 2 months. The oral vaccine (also called the Sabin vaccine), which contains a weakened or attenuated live virus, is given by mouth.
The oral vaccine is administered in other countries, and the current spread in New York is linked to a vaccine-derived virus that’s also been detected in the UK and Israel. In its statement this week, the CDC said that these viruses are not caused by children getting the polio vaccine.
Dr. Amesh Adalja is an infectious disease physician and senior scholar at the Johns Hopkins Center for Health Security. He says that the oral polio vaccine is still given in other countries because it’s cheaper and easier to administer (no needles needed), but it also “provides much more robust immunity.”
“The Sabin vaccine was used in the US for some time but as polio risks abated the Salk vaccine (injectable shot) became favored,” Adalja said in an email.
According to Kedl, the oral polio vaccine is so effective against infection because it stops the virus where it starts: the mouth. Polio enters the body through the mouth, usually through contaminated hands from the stool of an infected person. This is the same reason some researchers say a nasal COVID-19 vaccine will be more effective at preventing infection, because the respiratory virus enters through the nose.
But while highly effective against polio, the live vaccines do carry the risk of reverting back to more contagious forms.
“Polio is the poster child for why attenuated vaccines are so good, and why we also need to always be developing a more subunit or killed-vaccine approach,” Kedl said.
Oral polio vaccines aren’t available in the US anymore, but they’re still a big part of polio eradication efforts in other countries.
Ramesh Lalwani/Getty ImagesHow effective is the polio vaccine?
The CDC says that three doses of IPV (the inactive shots currently available in the US) are at least 99% effective at preventing paralysis caused by polio, and that two doses are 90% effective. Even for a vaccine that helped eradicate a disease, that seems really high. But while the vaccines haven’t been fully put to the test, that effectiveness rings true with Kedl.
“It’s definitely one of the most successful vaccines, in either of its forms, that has ever been made,” Kedl said. “Not because the vaccines themselves are so high-tech and fantastic, it’s just that polio itself is really susceptible to a pretty moderate immune response.” That is, we might need fewer antibodies produced from the vaccine to protect us against polio compared with other viruses.
“Polio seems to be very susceptible to being shut down by a reasonably modest vaccine response,” he noted. “Thank God.”
Do I need another polio vaccine or booster?
With just local spread in New York, the CDC hasn’t made any changes to its vaccine recommendations for the general public at this time.
“Boosters are really only recommended by CDC in special circumstances, including travel to areas in which wild polio is present or in which vaccine-derived strains are circulating,” Adalja said. “The state of New York has broadened that recommendation to include health care workers and wastewater workers.”
Health officials in New York are urging everyone to start their polio vaccine series as soon as possible if they haven’t yet – including adults who were never vaccinated, or can’t remember if they were. If you live anywhere in the US and haven’t been vaccinated against polio, reach out to your doctor.
The information contained in this article is for educational and informational purposes only and is not intended as health or medical advice. Always consult a physician or other qualified health provider regarding any questions you may have about a medical condition or health objectives.
