Poliovirus has been eradicated from most of the world due to mass vaccination efforts of the World Health Organization and Global Polio Eradication Initiative in the latter half of the 20th century. However, polio remains endemic in a few areas of the world with fewer than 200 cases reported annually over the past five years. While still rare, vaccine-derived polio is more common than wild (naturally occurring) poliovirus infection, with 682 cases reported in 2021 compared to six cases of wild polio in the same year.