Since 1988, when the World Health Assembly established the Global Polio Eradication Initiative (GPEI), wild poliovirus subtype-2 and subtype-3 have been successfully eradicated. The number of wild poliovirus cases across the world have sharply dropped by more than 99.9%.
Today, Afghanistan and Pakistan are the only countries where indigenous wild poliovirus subtype-1 transmission continues uninterrupted.
Rise in cases
Last year, the number of wild poliovirus subtype reported from Afghanistan and Pakistan shot up to 22 (two in Afghanistan, and 20 in Pakistan), from just five such cases in 2021. All the 20 cases reported in Pakistan were from security-compromised districts in Khyber Pakhtunkhwa province, representing a 19-fold increase over the single case reported in 2021. As of May 10, 2023, one case of wild poliovirus subtype-1 (WPV1) was reported in Khyber Pakhtunkhwa. In the case of Afghanistan, the latest reported WPV1 case was on August 29, 2022.
This year, as of May 10, one WPV1 case has been reported in Pakistan (February 20, 2023), while two cases have been detected from environmental samples. In contrast, there have been no wild poliovirus subtype-1 cases reported this year in Afghanistan, while 18 positive environmental samples have been reported so far this year.
Cause for concern
According to a recent report in the Morbidity and Mortality Weekly Report (MMWR), 859 cases of circulating vaccine-derived polioviruses (cVDPVs) have been reported last year. This marks an increase of 23% (698 cases) increase in such cases a year earlier — 2021. But what is particularly concerning is the fact that circulating vaccine-derived polioviruses have been reported from countries where poliovirus transmission had long been eliminated such as Canada, Israel, the U.K. and the U.S. In addition, there has been co-circulation of multiple poliovirus types occurring in multiple countries globally — Democratic Republic of the Congo (DRC), Israel, Malawi, Mozambique, Republic of the Congo, and Yemen.
The report warns that it is “unlikely” that the current global epidemiology of poliovirus transmission will make it possible to meet the 2022-2026 GPEI goal of detecting the last cases of WPV1 and cVDPV this year.
