In new setback for eradication campaign, poliovirus from Pakistan shows up in Africa

Health officials hope to squash outbreak quickly.

A wild poliovirus has made a leap from Pakistan to the African continent, where it has paralyzed a 3-year-old girl in Malawi—the first wild polio case in the country since 1992.

The case, announced on 17 February by the Malawi government, is the latest setback for the global campaign to end polio once and for all. But the Global Polio Eradication Initiative (GPEI) hopes it can limit the damage by stopping the outbreak quickly. Pakistan and Afghanistan are the last two countries that are endemic for the wild virus, which means circulation there has never stopped. Occasionally, the virus spills over from these entrenched reservoirs. The last “exportation” from the region was in 2013, when a virus from Pakistan sparked an outbreak in Syria.

Africa is battling big outbreaks of vaccine-derived polio, which occur in areas of low immunization when the live but attenuated virus in the oral polio vaccine reverts and regains its ability to paralyze and spread. But the last known case of wild polio on the continent occurred in 2016 in Borno state in Nigeria, and Africa was officially certified free of wild poliovirus in August 2020.

Because polio spreads quickly and “silently”—just about one in 200 infected children becomes paralyzed—even a single detection of the virus is considered an outbreak. But GPEI has a history of quashing these imported outbreaks quickly with rapid vaccination campaigns; the goal is to stop them within 6 months, before the virus becomes entrenched.

The girl, who lives in Malawi’s capital, Lilongwe, was paralyzed on 19 November 2021. Through sequence analysis of her poliovirus, the U.S. Centers for Disease Control and Prevention (CDC) and the regional reference lab in South Africa have just confirmed she was struck by a relative of wild type 1 poliovirus that circulated in Sindh province in Pakistan in October 2019. The new case means the virus has been lurking undetected since then.

GPEI analysts don’t know yet when the virus arrived in Malawi and how far it may have spread. The quality of polio surveillance in Malawi has slipped during the COVID-19 pandemic. GPEI is also assessing the risk of spread to other countries, because there is a lot of population movement from Malawi to Mozambique, Zambia, and Tanzania. And it is figuring out the vaccination strategy—which vaccine to use, and how broadly.

Although Malawi is now considered a “wild-polio–affected country,” the African continent will still be considered free of wild poliovirus unless it circulates for 12 months or more.

The case shows, again, that “polio anywhere is a threat to children everywhere,” says John Vertefeuille, a CDC polio specialist. “One child paralyzed is one too many and it is a tragedy for the girl and her family,” adds Aidan O’Leary, director of GPEI, which is based at the World Health Organization’s headquarters in Geneva. “It simply underscores the importance of prioritizing immunization activities everywhere while focusing on permanently interrupting polio transmission in Pakistan and Afghanistan.”

https://www.science.org/content/article/new-setback-eradication-campaign-poliovirus-pakistan-shows-africa