Serious concern: wild poliovirus type 1 cases in Pakistan, Afghanistan

The ambitious goal of eradicating wild poliovirus type 1 (WPV1) by 2026 seems to have become more challenging. WPV1, endemic only in Pakistan and Afghanistan, has shown signs of resurgence since 2023. With Afghanistan and Pakistan reporting six WPV1 cases each in 2023 (two in Afghanistan and 20 in Pakistan in 2022), it may seem that the total incidence of type 1 cases in both countries in 2023 has almost halved. However, there seems to be an upward trend with six cases reported in Afghanistan and five in Pakistan already this year. If this trend continues, the total number of cases reported from both countries may approach or even exceed the 2022 figures. Concerns regarding WPV1 are not limited to the number of pediatric cases. Circulation of the virus in the environment appears to be increasing, and most importantly, after a two-year gap, an increasing number of positive environmental samples have been collected in Pakistan from cities that have historically been reservoirs of the virus from 2023 to early June this year. Last year, 125 positive environmental samples were collected from 28 districts in Pakistan. Of these, 119 belonged to genetic cluster (YB3A), suggesting introduction from Afghanistan. By June 1 this year, there were 153 positive environmental samples from 39 districts. As of April 8, 2024, 34 positive environmental samples have been collected from Afghanistan.

According to the World Health Organization, positive environmental samples in “epidemiologically significant areas and historical epicenters” such as Karachi, Quetta, and Peshawar-Khyber districts in Pakistan and Kandahar in Afghanistan indicate a significant risk to the gains made in the past. The increasing positivity rate of environmental samples reflects that the polio campaign has not actually achieved the desired coverage, and false fingerprinting without vaccination is a persistent problem. Although urban children in Pakistan are largely vaccinated, there is an increasing risk of unvaccinated or under-vaccinated children contracting the virus. In 2023, two of the six cases occurred in the city of Karachi. The situation in Pakistan appears to be worse than in Afghanistan, with the actual spread of WPV1 “being seen mainly in Afghanistan in 2022, with detections in Pakistan in 2023 and 2024.” There is also a significant risk of international spread from Pakistan, especially to Afghanistan. More than 500,000 Afghan refugees have been forcibly displaced from Pakistan, and another 800,000 are expected to be displaced soon, increasing the risk of cross-border spread of the virus. Southern Afghanistan has a large population of unvaccinated or immunocompromised children, increasing the risks posed by returning refugees.