In 1994, the Region of the Americas was the first in the world to be certified polio-free by the World Health Organization (WHO), a milestone achieved after concerted effort by countries with the support of the Pan American Health Organization (PAHO). But vaccination rates in children with all three doses of the polio vaccine stood at 79% in 2021, putting the region at risk of the reintroduction of the disease.

Recently an unvaccinated 20-year-old man in the United States, who presented with paralysis, was diagnosed with vaccine-derived poliovirus (VDPV), a strain related to the weakened poliovirus contained in the oral polio vaccine (OPV). On rare occasions, when replicating in the gastrointestinal tract, the strain may spread in communities that are not fully vaccinated against polio.