How Well Do Polio Vaccines Work?

Polio may be spreading among people who are not vaccinated against the disease in the United Kingdom. Last month, the U.K. Heath Security Agency said a sewage plant in London repeatedly found traces of poliovirus in routine sewage sample testing from February through May.

While there haven’t been any reported cases of people developing a polio infection, many people are wondering why this is happening and if it is something we need to be concerned about. After all, polio has been eradicated in the United States since 1979, and in the United Kingdom since 2003.

“Infectious disease experts in the U.S. are closely watching this recent finding,” Julianne Elizabeth Burns, MD, pediatric infectious diseases physician at Stanford Children’s Health, told Verywell via email. “However, the risk to people in the U.S. is low since there are high rates of vaccination against poliovirus. Poliovirus vaccination protects against naturally occurring (wild) polio viruses and vaccine-derived polioviruses.”

If polio were to make a comeback, how well would your routine vaccinations protect you? Extremely well, experts say; the four-dose vaccine regimen most Americans receive as kids is 99%–100% effective after only three doses.

Different Types of Polio Vaccines Explain the Wastewater News

There are two different types of polio vaccine administered around the world: the live attenuated oral polio vaccine (OPV) and the inactivated polio vaccine (IPV).

The inactivated polio vaccine was first introduced in 1955. In 1961, the oral option emerged as a more convenient way to vaccinate children, since it avoided a shot in the arm or the leg.

Only the live OPV version can be shed through stool for several weeks after vaccination. So while they didn’t contract polio in the wild, it’s likely some people in London experienced “vaccine-derived poliovirus” after receiving the oral polio vaccine. Now, it’s showing up in their poop.

Burns said there is a risk that vaccine-derived poliovirus can spread to other people through the fecal-oral route, and genetically mutate back to the “wild” naturally occurring poliovirus over time. That’s why the inactivated polio vaccine has been the only polio vaccine used in the U.S. since 2000 and the U.K. since 2004. It cannot be shed through the stool or spread polio to others.

“The polio virus found in the wastewater in the U.K. is most likely a version of the oral polio vaccine virus that someone received in another country,” Burns said. “Luckily, the risk of getting sick from these vaccine-derived versions of the poliovirus is extremely low for anyone who has been immunized against polio. However, there is a risk to people who have not been immunized against polio.”

Polio Vaccines Are Intended to Last a Lifetime

The Centers for Disease Control and Prevention (CDC) says it is unknown exactly how long immunity from the inactivated polio vaccine lasts, but people are “most likely protected for many years after a complete series of IPV.”

A booster is only necessary once in a lifetime if an adult is at an increased risk of exposure to polio.

For adults who were not vaccinated as children and find themselves at a higher risk of being exposed to polio, the CDC recommends a three-dose schedule:

• The first dose at any time
• The second dose 1 to 2 months later
• The third dose 6 to 12 months after the second dose

The CDC recommends children get the inactivated polio vaccine to protect against polio as part of the routine childhood immunization schedule.

The vaccine regimen includes four doses at various ages:

• 2 months old
• 4 months old
• 6 through 18 months old
• 4 through 6 years old

“Unfortunately, during the COVID-19 pandemic, more children have fallen behind in receiving recommended vaccines,” Burns said. “We live in an interconnected world and there is still a risk of travelers bringing wild polio virus or vaccine-derived polio virus that can cause polio illness to the U.S. Vaccination protects against both wild polio viruses and vaccine-derived polio viruses. If we maintain high levels of vaccination coverage, the risk of these polio viruses spreading is very low.”