Transmission rates for Wild poliovirus (WPV1) and circulating vaccine derived poliovirus (cVDPV) continue to fall, but the risk of inter-country transmission remains high, leading an emergency committee convened by the World Health Organization (WHO) to renew the Public Health Emergency of International Concern (PHEIC) for polio.
According to the WHO, no new WPV1 cases have been reported since January 2021 when two WPV1 cases occurred, one each from Pakistan and Afghanistan, compared to 94 WPV1 cases during the same time period in 2020. The overall proportion of specimens that are positive has declined from almost 60% in 2020 to less than 15% in 2021 to date with no detection in Afghanistan since February 23 and only ten isolates in Pakistan since March 31. The most recent detection in 2021 was in Afghanistan and was a result of importation from Pakistan.
WHO warned against complacency, noting gaps in vaccination efforts. “The ongoing inaccessibility in many provinces of Afghanistan coupled with increasing military conflict remains a major risk. Around three million children were persistently missed in 2020 and 2021 so far, with around one million children in Southern Afghanistan missing out on vaccination for almost three years.”
Meanwhile the number of cases of cVDPV2 in 2021 so far is 170, compared to the total cases in 2020 of 1,069.
In Afghanistan in 2021, all cVDPV2 cases occurred in inaccessible areas. The total number of lineages detected in 2021 is 15 so far, compared to 36 in 2020, and 44 in 2019. Based on analysis of isolates by genomic analysis, in the three months from January to March 2021, there have been eight episodes of international spread of cVDPV2. China has reported an outbreak of cVDPV3 due to local emergence, bringing the total number of infected countries to 31.
“Although heartened by the apparent progress, the committee unanimously agreed that the risk of international spread of poliovirus remains a Public Health Emergency of International Concern (PHEIC) and recommended the extension of temporary recommendations for a further three months. The committee recognizes the concerns regarding the lengthy duration of the polio PHEIC, but concludes that the current situation remains risky, with clear ongoing risk of international spread and ongoing need for coordinated international responses,” the WHO said.