Polio eradication

A public health effort to eliminate all cases of poliomyelitis (polio) infection around the world, begun in 1988 and led by the World Health Organization (WHO), the United Nations Children's Fund (UNICEF) and the Rotary Foundation, has reduced the number of annual diagnosed wild polio cases from the hundreds of thousands to 22 in 2017.

Of the three strains of polio virus, the last recorded wild case caused by type 2 (WPV2) was in 1999. Type 3 (WPV3) is last known to have caused polio on 11 November 2012, with all wild-virus cases since that date being due to type 1 (WPV1). Mutated vaccine strains can also result in polio, and so-called circulating vaccine-derived cases of type 1 (cVDPV1) and 2 (cVDPV2) continue to be detected. If polio is the next disease to be successfully eradicated, this will represent only the third time this has ever been achieved, after smallpox and rinderpest.

The goal of eradicating polio worldwide has attracted international and media attention, with a reduction of some 99% of cases in the last quarter of the 20th century. The first ten years of the 21st century saw only erratic progress in further reducing the number of cases, which led to getting rid of the last 1% being described as "like trying to squeeze Jell-O to death". Since 2011 incidence rates of the disease have dropped dramatically, and with large reductions continuing through to 2017, hopes for eliminating polio have been rekindled.

India is the latest country to have officially stopped endemic transmission of polio—with its last reported case in 2011. Only three countries remain where the disease is endemic—Afghanistan, Pakistan and Nigeria.

Eradication of polio has been defined in various ways—as elimination of the occurrence of poliomyelitis even in the absence of human intervention, as extinction of poliovirus, such that the infectious agent no longer exists in nature or in the laboratory, as control of an infection to the point at which transmission of the disease ceased within a specified area, and as reduction of the worldwide incidence of poliomyelitis to zero as a result of deliberate efforts, and requiring no further control measures.

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