Eradication of wild poliovirus type 3

The World Health Assembly launched the Global Polio Eradication Initiative in 1988, prompted by Rotary International's campaign. That year polio paralyzed more than 350,000 children in 125 countries. India reported its last wild case in 2011, and WHO's South-East Asia Region was declared polio-free in 2014. By 2019 the world count of wild poliovirus cases had fallen to 176, all in two countries. Wild poliovirus comes in three types. Type 2 went first: its last case was in 1999, and it was declared eradicated in September 2015.

Type 3 went next. Its last known case was in northern Nigeria in 2012. On 24 October 2019 the Global Commission for the Certification of Poliomyelitis Eradication, an independent panel of experts, concluded that type 3 had been eradicated worldwide, and its chair, David Salisbury, presented the certificate. Salisbury noted that no wild type 1 had been detected anywhere in Africa since 2016.

The eradication of type 2 changed the vaccine. Most outbreaks of circulating vaccine-derived poliovirus were caused by the type 2 strain in the oral vaccine, so in 2016 countries made a coordinated global switch from trivalent oral vaccine to a bivalent vaccine containing only the Sabin type 1 and type 3 strains. Vaccine-derived type 2 did not vanish with it: a 2020 CDC report counted 41 outbreaks of circulating vaccine-derived type 2 detected by the WHO Global Polio Laboratory Network after the switch.

With types 2 and 3 certified gone, wild poliovirus type 1 was the only wild strain left in circulation, confined to Afghanistan and Pakistan.