On July 21, 2022, a man in Rockland County, New York, was reported to have experienced partial paralysis as a result of polio infection. As the first case of polio since 2013, this news reached national attention. In the weeks following, the virus was found in wastewater samples from both Rockland County and neighboring Orange County. The man from Rockland County was unvaccinated and, in fact, only 60 percent of people in the entirety of Rockland County had received a polio vaccination, well below the national average. In response, the Rockland County Department of Health supplied catch-up vaccinations for residents who had not completed the 3-dose childhood vaccination series with inactivated polio vaccine (IPV), as is the current CDC recommendation. From stool samples, the man was determined to have been infected with vaccine-derived poliovirus type 2 (VDPV2).
Polio exists in several forms. There are three strains of the wild-type virus; of these, the wildtype poliovirus types 2 and 3 were globally eradicated in 2019 and 1999, respectively, after a worldwide vaccination effort. Wildtype polio infections currently only exist in two countries – Afghanistan and Pakistan. All other polio infections are a result of the virus from the oral polio vaccine (OPV) spreading in under-immunized communities. This “live vaccine” contains an attenuated, or weakened, form of the poliovirus, whereas the IPV, given as an intramuscular injection, is an inactivated form of the virus. While the OPV was largely phased out in the United States by 2000 in favor of the IPV, the OPV is less expensive to manufacture and easier to administer (orally). These advantages make it an ideal candidate for use in resource limited settings and areas where extensive vaccination is needed. However, when vaccination rates are low, there is a small risk of the attenuated virus spreading, causing a vaccine-derived poliovirus (VDPV) infection.
VDPV occurs in communities with low vaccination rates as the susceptible population is larger, which allows the VDPV to spread and gain mutations. As most polio infections are asymptomatic, it is likely many people infected during the New York outbreak were unaware they were infectious and freely passed the virus to other unvaccinated individuals. The strain of virus found in New York’s wastewater was found to be related to concurrent outbreaks in London and Jerusalem; while the United Kingdom has used the IPV since 2004, Israel uses both the IPV and the OPV.
While VDPV infection from the OPV is extremely rare (only 1,000 cases reported in the past 20 years), it is still possible to develop paralysis from the infection. Our greatest protection against VDPV infection is to maintain high vaccination rates among all communities – especially with the IPV when available – and to continue with the global effort to eradicate all strains of wildtype polio.
Pamela is a current third-year medical student at the University of Texas Medical Brach in Galveston. She is interested in Infectious Disease and hopes to pursue this passion in the future.
Sources
Link-Gelles R, Lutterloh E, Schnabel RP, et al. Public Health Response to a Case of Paralytic Poliomyelitis in an Unvaccinated Person and Detection of Poliovirus in Wastewater – New York, June-August 2022. MMRW Morbidity and Mortality Weekly Report 2022;71(33):1065-1068. Doi: https://dx.doi.org/10.15585/mmwr.mm7133e2.
Global eradication of wild poliovirus type 3 declared on World Polio Day. World Health Organization 24 Oct 2019. Retrieved from https://www.who.int/news-room/feature-stories/detail/two-out-of-three-wild-poliovirus-strains-eradicated#:~:text=There%20are%20three%20individual%20and,irreversible%20paralysis%20or%20even%20death.
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Centers for Disease Control and Prevention. Vaccine-Derived Poliovirus. Vaccines and Preventable Diseases 20 Sept 2022. Retrieved from https://www.cdc.gov/vaccines/vpd/polio/hcp/vaccine-derived-poliovirus-faq.html.