Grave concern: On wild-type poliovirus type-1 cases in Pakistan, Afghanistan

The risk of international spread of wild type-1 polio cases from Pakistan is great

The ambitious goal of eradicating wild-type poliovirus type-1 (WPV1) by 2026 appears to have become tougher. WPV1, which is endemic only in Pakistan and Afghanistan, is showing signs of a resurgence since 2023. With Afghanistan and Pakistan reporting six WPV1 cases each in 2023 — there were two cases in Afghanistan and 20 cases in Pakistan in 2022 — the total incidence of type-1 cases in both countries in 2023 might appear to have nearly halved. But with six cases in Afghanistan and five cases in Pakistan already this year, there appears to be an uptick. If this continues, the total cases being reported from the two countries might be close to or even surpass the 2022 numbers. The concern about WPV1 is not limited to the number of cases in children. The circulation of the virus in the environment is seen to be rising, and, most importantly, after a gap of two years, positive environmental samples have been increasingly collected in Pakistan, in 2023 and till early June this year, from cities which have been historical reservoirs for the virus. Last year, 125 positive environmental samples were collected from 28 districts in Pakistan. Of these, 119 belonged to a genetic cluster (YB3A), which suggests that these were imported from Afghanistan. By June 1 this year, there have been 153 positive environmental samples from 39 districts. As of April 8, 2024, 34 positive environmental samples were collected from Afghanistan.

According to the World Health Organization, the presence of positive environmental samples in “epidemiologically critical areas and historical reservoirs” such as Karachi, Quetta and the Peshawar-Khyber blocks in Pakistan, and Kandahar in Afghanistan, represents a significant risk to the gains made in the past. Rising positive environmental samples are a reflection of polio campaigns not really achieving their desired coverage; fake finger marking sans vaccination is a persisting problem. Though children in Pakistan’s cities are largely immunised, there is a heightened risk of the virus striking any unvaccinated or not fully vaccinated children — in 2023, two of the six cases were from Karachi city. The situation in Pakistan appears worse than it is in Afghanistan with the actual spread of WPV1 seen “predominantly in Afghanistan in 2022 now being detected in Pakistan in 2023 and 2024”. There is also the grave risk of international spread from Pakistan, particularly to Afghanistan. With over 0.5 million Afghan refugees forced to leave Pakistan, and an estimated 0.8 million to be evicted soon, there is an increased risk of cross-border spread of the virus. There is a large pool of unvaccinated and under-immunised children in southern Afghanistan, increasing the risk that returning refugees can pose.