Polio eradication

Polio eradication, the permanent global cessation of circulation of the poliovirus and hence elimination of the poliomyelitis (polio) it causes, is the aim of a multinational public health effort begun in 1988, led by the World Health Organization (WHO), the United Nations Children's Fund (UNICEF) and the Rotary Foundation.^[1] These organizations, along with the U.S. Centers for Disease Control and Prevention (CDC) and The Gates Foundation, have spearheaded the campaign through the Global Polio Eradication Initiative (GPEI). Successful eradication of infectious diseases has been achieved twice before, with smallpox in humans^[2] and rinderpest in ruminants.^[3]

Prevention of disease spread is accomplished by vaccination. There are two kinds of polio vaccine—oral polio vaccine (OPV), which uses weakened poliovirus, and inactivated polio vaccine (IPV), which is injected. OPV is less expensive and easier to administer, and can spread immunity beyond the person vaccinated, creating contact immunity. It has been the predominant vaccine used. However, under conditions of long-term vaccine virus circulation in under-vaccinated populations, mutations can reactivate the virus to produce a polio-inducing strain, while OPV can also, in rare circumstances, induce polio or persistent asymptomatic infection in vaccinated individuals, particularly those who are immunodeficient. Being inactivated, IPV is free of these risks but does not induce contact immunity. IPV is more costly and the logistics of delivery are more challenging.

Nigeria is the latest country to have officially stopped endemic transmission of wild poliovirus, with its last reported case in 2016.^[4] Wild poliovirus has been eradicated in all continents except Asia, and as of 2020^[update], Afghanistan and Pakistan are the only two countries where the disease is still classified as endemic.^[5][6]

Recent polio cases arise from two sources, the original "wild" poliovirus (WPV), and the much more prevalent mutated oral vaccine strains, known as circulating vaccine-derived poliovirus (cVDPV). Vaccines against each of the three wild strains of polio have given rise to strains of cVDPV, with cVDPV2 being most prominent. cVDPV caused 864 confirmed paralytic polio cases worldwide in 2022.^{[citation needed]}

There were 30 confirmed WPV cases in 2022, a decrease from 2019's 5-year high of 176, a 95.8% reduction from the 719 diagnosed cases in 2000 and a 99.91% reduction from the 35,251 reported cases when the eradication effort began in 1988. Total polio cases (combined wild and circulating vaccine-derived) have dropped 97.5% from 35,251 (reported) in 1988 to 894 (confirmed) in 2022. Of the three strains of WPV, the last recorded wild case caused by type 2 (WPV2) was in 1999, and WPV2 was declared eradicated in 2015. Type 3 (WPV3) is last known to have caused polio in 2012, and was declared eradicated in 2019.^[7] All wild-virus cases since that date have been due to type 1 (WPV1).^{[citation needed]}