Paralytic poliomyelitis was thought to be nearly eradicated worldwide until a handful of cases were reported early this year in Pakistan, Malawi, and Mozambique. Then, last summer, London, Jerusalem, and New York City found the polio virus in wastewater-evidence it was circulating among city residents and a stark reminder of the global reach of this highly contagious disease.
Most polio infections go undiagnosed; they are either asymptomatic or produce only mild, flu-like symptoms. Paralysis occurs in from one in 200 to one in 2,000 infected individuals, depending on the virus type. Before the advent of polio vaccines in 1955, more than 15,000 U.S. children were paralyzed each year by the virus. Vaccination has proven to be highly effective, but pockets of unvaccinated people still exist in the United States and many parts of the world. An unvaccinated adult residing in a suburb of New York City who became ill last summer is the first U.S. case of paralytic polio since 2013.
Many factors contribute to the world's inability to achieve universal vaccination. Among them are wars such as the current conflicts in Yemen and Ukraine; the worldwide refugee crisis (estimated to total 100 million displaced people); decreases in all types of vaccination during the COVID-19 pandemic; unstable health systems in many countries; and vaccine hesitancy.
"Wild type" poliovirus, so-called because it circulates in the natural environment, is endemic only to Pakistan and Afghanistan. "Vaccine-derived" paralytic polio is the greater threat today, accounting for 1,900 cases in 33 countries between January 2020 and April 2022. This is due to the use of inexpensive oral polio vaccine (OPV) in many parts of the world. Unlike the injectable vaccine containing killed virus used in the United States and other high-income countries, OPV contains a weakened version of poliovirus that can be shed in stool and circulate long enough to mutate to a virulent form.
A global consortium of public-private partners, including the World Health Organization; Rotary International; the Centers for Disease Control and Prevention; UNICEF; the Gates Foundation; and Gavi, the Vaccine Alliance, is working to eradicate polio, but collaboration with local community leaders and targeted clinical efforts are also needed. Vaccination efforts should be continuous, and active wastewater surveillance for poliovirus should be ongoing. And, as with the COVID-19 pandemic, experts say developed countries must stand ready to help less affluent countries strengthen their prevention efforts.-Betsy Todd, MPH, RN