Ask the Experts: Polio

Since the Global Polio Eradication Initiative was launched in 1988, the number of polio cases worldwide has declined by more than 99.99%. Among the three wild poliovirus (WPV) serotypes, only type 1 (WPV1) has been detected since 2012. Global eradication of type 2 WPV was declared in 2015; type 3 WPV was declared eradicated in 2019. The number of detected WPV1 cases has reached a historic low (33 cases in 2018 and 176 in 2019) in the last two countries with endemic WPV1 transmission (Afghanistan and Pakistan). However, during 2021–2022, Malawi and Mozambique reported nine WPV1 cases that were genetically linked to Pakistan. These cases highlight the risk for importation and the importance of maintaining enhanced global monitoring and surveillance.

This decline in polio cases worldwide is attributable primarily to use of the live, attenuated oral poliovirus vaccine (OPV) in national routine immunization schedules and mass vaccination campaigns. The success and safety record of OPV use is offset by the rare emergence of genetically divergent vaccine-derived polioviruses (VDPVs), whose genetic drift from the parental OPV strains indicates prolonged replication or circulation. Circulating VDPVs (cVDPVs) can emerge in areas with low immunization coverage and can cause outbreaks of paralytic polio. In addition, immunodeficiency-associated VDPVs (iVDPVs) can emerge in people with primary immunodeficiencies and can replicate and be excreted for years. During January 2020–April 2022, a total of 1,856 cVDPV cases were identified in 33 countries. In July 2022, a case of paralytic polio caused by vaccine-derived poliovirus type 2 (VDPV2) was confirmed in an unvaccinated young adult from Rockland County, New York.

In April 2016, all OPV-using countries switched from using trivalent OPV (tOPV; Sabin types 1, 2, and 3) to bivalent OPV (bOPV; Sabin types 1 and 3). To control and prevent cVDPV2 outbreaks, traditional monovalent type 2 OPV (mOPV2) has been distributed in affected countries; in addition, a novel monovalent type 2 OPV (nOPV2) that is less likely to produce cVPDV disease was listed under an Emergency Use Authorization (EUL) by the World Health Organization (WHO) in November 2020, (Bio Farma, Indonesia) to address the rising cases of cVDPV2. As of March 2023, close to 600 million doses of the nOPV2 have been used across 28 countries in outbreak response.

Additional information about the polio eradication program is available on the CDC website at www.cdc.gov/polio.

What is the routine schedule for giving inactivated polio vaccine (IPV, brand name IPOL, Sanofi) to children?

In the U.S., all infants and children should receive 4 doses of IPV at ages 2, 4, 6–18 months, and 4–6 years. The first dose may be given as early as 6 weeks of age. The final dose should be administered at 4 years of age or older, regardless of the number of previous doses, and should be given 6 months or more after the previous dose. A fourth dose in the routine IPV series is not necessary if the third dose was given at 4 years of age or older and 6 months or more after the previous dose.

Infants and children traveling to areas where there has been wild or vaccine-derived poliovirus (cVDPV) circulation in the last 12 months should be vaccinated according to the routine schedule. If the routine series cannot be administered within the recommended intervals before protection is needed, an accelerated schedule can be used: 1) the first dose should be given to infants 6 weeks of age and older, 2) the second and third doses should be administered at 4 weeks or more after the previous doses, and 3) the minimum interval between the third and fourth doses is 6 months. If the age-appropriate series is not completed before departure, the remaining IPV doses to complete a full series should be administered when feasible, at the intervals recommended for the accelerated schedule. If doses are needed while residing in the affected country, the polio vaccine that is available (IPV or oral polio vaccine [OPV]) may be administered.

In addition to single-antigen IPV, five pediatric combination vaccines that contain IPV vaccine are licensed and recommended for use in the United States: DTaP-HepB-IPV (Pediarix, GSK), DTaP-IPV/Hib (Pentacel, Sanofi), DTaP-IPV (Kinrix, GSK), DTaP-IPV (Quadracel, Sanofi), and DTaP-IPV-Hib-HepB (Vaxelis, MSP Vaccine Company).

What is the schedule for people age 4 years or older who have not completed their IPV polio vaccine series on schedule?

The schedule for polio vaccination for unvaccinated or under-vaccinated older children and adults is 2 doses of IPV separated by 4–8 weeks, and a third dose 6–12 months after the second dose (the final dose must be given after the fourth birthday). If an accelerated schedule is needed, the first two doses should be separated by at least 4 weeks and the third (final) dose given at least 6 months after the second dose. In June 2023, the CDC’s Advisory Committee on Immunization Practices (ACIP) recommended that any adult known or suspected to be unvaccinated or incompletely vaccinated should complete a primary IPV series.

A 4-year-old’s vaccine records show that she had four doses of inactivated polio vaccine, or IPV, given at 2 months, 4 months, 6 months, and age 2 years. Should she have a booster dose? [Video]

Should adults get vaccinated against polio?

Most adults residing in the United States are presumed to be protected against polio because they received routine childhood immunization and have only a small risk of exposure to poliovirus in the United States. For decades, routine polio vaccination of U.S. residents 18 years of age and older, including those working in healthcare or in healthcare-related training, was not recommended.

In June 2022, a case of paralytic polio caused by vaccine-derived poliovirus type 2 (VDPV2) was confirmed in an unvaccinated young adult from Rockland County, New York, and wastewater surveillance in the region repeatedly detected evidence of poliovirus over the following months, suggesting the presence of an unknown number of asymptomatically infected people in the community. People who are fully vaccinated with IPV are protected from polio illness but may shed virus in their feces, if exposed. This experience underscored the ongoing risk, however small, of paralytic polio among incompletely vaccinated people in the United States.

CDC’s ACIP recommended in June 2023, that all adults (18 years and older) who are known or suspected to be unvaccinated or incompletely vaccinated against polio should complete a primary 3-dose vaccination series with IPV: 2 doses of IPV administered at an interval of 4–8 weeks; and a third dose 6–12 months after the second. If an adult previously received only one or two documented doses of polio vaccine (either trivalent OPV or IPV), the person should receive the remaining dose(s) of IPV necessary to complete the series, regardless of the interval since the last dose. It is not necessary to restart the vaccination series.

Polio vaccination with a complete primary series is recommended for all travelers to countries with wild poliovirus (WPV) or vaccine-derived poliovirus (VDPV) circulation. WHO recommends that countries affected by WPV or cVDPV require long-term visitors (4 weeks or longer) to provide proof of polio vaccination before leaving the country. For additional information on countries with WPV or VDPV circulation, as well as country-specific requirements for documentation of vaccination, consult the CDC Travelers’ Health website (wwwnc.cdc.gov/travel/).

Adults who have completed a routine series of polio vaccine (with trivalent OPV or IPV in any combination) are considered to have lifelong immunity to poliomyelitis, but data on duration of immunity are lacking. In June 2023, ACIP affirmed and clarified its longstanding recommendation that certain adults at increased risk of exposure to poliovirus may receive a single lifetime adult booster dose of IPV. Adults in situations that put them at increased risk of poliovirus exposure include: travelers going to countries where polio is epidemic or endemic; laboratory and healthcare workers who handle specimens that might contain polioviruses; and, healthcare workers or other caregivers who have close contact with a person who could be infected with poliovirus.

We have an adult who was diagnosed with polio as a child with some residual effects. This adult will be traveling overseas and the CDC travel website recommends a dose of polio vaccine. Should he be vaccinated with polio vaccine even though he had polio in the past?

Immunity to one of the serotypes of polio does not produce significant immunity to the other serotypes. A history of having recovered from polio disease should not be considered evidence of immunity to polio. You should complete a primary series of IPV if he is known or suspected to have been unvaccinated or incompletely vaccinated against polio. If he received a primary series in childhood, a single adult booster dose may be given before travel to an area where polio vaccination is recommended.

How did ACIP alter its recommendations for polio (IPV) vaccination of unvaccinated or incompletely vaccinated adults in June 2023?

In June 2023, ACIP recommended that all adults (18 years and older) in the United States who are known or suspected to be unvaccinated or incompletely vaccinated against polio should complete a primary 3-dose vaccination series with IPV: 2 doses of IPV administered at an interval of 4–8 weeks; and a third dose should be administered 6–12 months after the second. Previously, ACIP did not recommend IPV vaccination of unvaccinated or incompletely vaccinated adults who lacked a specific increased risk for exposure to polio (e.g., due to travel). Most U.S. adults may be presumed to be vaccinated against polio unless there is a specific reason to believe otherwise (e.g., an adult whose parents were known to have refused vaccinations). Rates of polio vaccination among children in the United States have been extremely high for decades.