What to Know About the Polio Vaccine

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 for decades. So when a case of polio with paralysis was confirmed in an unvaccinated person from New York in July, alarm bells went off. Further wastewater testing detected polio in more New York counties, indicating local community spread. In September, New York declared a disaster to increase the vaccine reach. Health officials everywhere are reminding people to get their children vaccinated against polio, which can cause paralysis and be deadly.

There are two kinds of polio vaccines: inactivated polio vaccines, which haven't been available in the US in over 20 years, and oral polio vaccines, which are still given out in other countries and are especially effective in places where there are outbreaks. Because of the polio spread in New York (which is linked to the strain also found in the UK and Israel), health officials could again introduce an oral polio vaccine, though a newer version of it. A panel that makes recommendations for the US Centers for Disease Control and Prevention met last week to discuss both polio vaccine types as a way "proactively to stay prepared," a CDC spokesperson said. The newer oral polio vaccine (nOPV2) hasn't been authorized or recommended yet.

"It will be a process. It's not something that we can pull the trigger on and have it appear overnight," Dr. Janell Routh, the CDC's leader for domestic polio, told CNBC on Friday. "There will be lots of thought and discussion about the reintroduction of an oral polio vaccine into the United States."  

Compared to the inactivated polio vaccine now offered in the US, the oral polio vaccine has some advantages, including easy administration and the ability to stop person-to-person transmission of the virus. But it also has some disadvantages, including the potential to mutate into a contagious form of the virus and, in very rare cases, cause paralysis in unvaccinated people. It's a vaccine-derived strain of polio that's circulating in New York, which is believed to have originated in another country that uses oral polio vaccines. 

While the shots we get now in the US are effective against polio, the oral vaccines may be able to further limit the spread of polio, according to information shared at a CDC advisory committee meeting. Should polio spread beyond where it's locally circulating, the hope is that introducing another tool would help us better respond to an outbreak. 

But we aren't there right now. Ross Kedl, immunologist and professor at the University of Colorado Anschutz School of Medicine, told CNET in September that polio is not a wide threat to the US right now — at least to those who've been vaccinated against it. The majority of us were fully vaccinated as children, and it's a requirement for attending most schools.

"Where it does cause troubles is in communities where the vaccine uptake is lower than it needs to be," Kedl said. 

In communities where vaccine rates are lower than normal — like Rockland County, where the polio case was reported in the US — the virus can again become an issue. About 60% of children living in Rockland County have been vaccinated against polio by their second birthday, according to state health department information. Comparatively, the CDC reports that about 92% of 2-year-olds nationwide have been vaccinated against polio. 

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.

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 a statement, 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 gut. Polio enters the body through the mouth, usually through contaminated hands from the stool of an infected person, and immunity in the gut (intestines) keeps the virus from getting to the nerves. This is a similar reason some researchers say a nasal COVID-19 vaccine will be more effective at preventing infection, because the respiratory virus enters through the nose or upper respiratory tract.

But while highly effective against polio, the live vaccines do carry the risk of the weakened virus mutating into 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.

How 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 in the US in decades, 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 the 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." Other people, including some child care workers in New York areas with community transmission, or people who might be at higher risk of coming into contact with someone with polio, may also get a booster. 

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.