In October 2019, the World Health Organization (WHO) announced the eradication of type 3 poliomyelitis. This followed the eradication of type 2, which was announced in 2015. Only type 1 remains in the wild, but the CDC, WHO, and other involved public health institutions are optimistic that it can be eradicated soon.
Types 2 and 3 have already been certified eradicated, but it's not impossible that the wild types could re-emerge naturally. (This actually happened in Nigeria in 2016, two years after the prior last reported natural cases in Africa.) This property of the virus has caused some reticence by the WHO about certifying the eradication--the last known type 2 case was in 1999, but the WHO didn't certify it until 2015.
When will the WHO certify the worldwide eradication of Polio?
This question will resolve on the date that the World Health Organization declares that polio has been eradicated from the wild everywhere on Earth. This announcement must include all known strains, mutations, and variants of polioviraus. Viruses contained in medical labs for research or vaccine development will not be considered to be "in the wild". If the WHO's announcement is not retracted by the WHO within 2 months, it will be considered a definitive announcement for resolution, even if it is later known to be mistaken or retracted.