Polio Laboratory Network - the “silent hero” that halted wild polio spread in Malawi, Mozambique

Alice Sihungwe is one of the sample collectors who has monitored wastewater every week since the outbreak was declared in Malawi: “We come here on Mondays and we take sewage samples from this site, operationalized by WHO. Then, we store them in the Community Health Sciences Unit (CHSU) until they are transported to the polio lab in South Africa for final polio testing.”

When a stool sample from a three-year-old boy suffering from paralysis near Lilongwe, Malawi, tested positive for wild poliovirus type 1 (WPV1) in late 2021, the discovery set off a chain of rapid and coordinated actions, triggering urgent laboratory and field investigations into the circulation of the virus.

The journey from sample collection to laboratory analysis is meticulously conducted, a crucial step in the process of determining the presence of viruses and devising effective containment strategies. It begins here, with environmental surveillance samples stored at the CHSU in Lilongwe, awaiting transportation to one of the Regional Polio laboratories in South Africa (NICD) for final polio testing.

On arrival at the laboratory in South Africa, highly trained technicians embark on a series of rigorous tests to confirm the presence of the poliovirus. These tests, often involving advanced molecular techniques, are aimed at detecting the specific serotype of virus circulation in the community, which will directly determine the type of vaccine to be administered in response.

When the laboratory results were shared with the Polio team, Dr Anfumbom Kfutwah, Regional Polio Laboratory coordinator at the WHO Regional Office for Africa, immediately understood the severity of the situation. “Thanks to our laboratory network, we confirmed that this was an imported wild poliovirus type 1 genetically linked to a strain circulating in Pakistan’s Sidh province in 2019. This proved once again that polio knows no borders, and that every country remains at risk until polio is eradicated everywhere,” he says.

It was the first of such detection in Malawi in more than three decades, and Mozambique subsequently reported eight other WPV1 cases in northern Tete Province.

The laboratory network mobilized quickly, conducting widespread surveillance to identify and isolate cases. Contingency plans were put in place to accommodate the surge in community contact and sewage samples. Their unwavering commitment and technical expertise formed the backbone of the region's response, ensuring that no stone was left unturned in the battle against polio.

Following the detections, Malawi and Mozambique, along with neighbouring countries –Tanzania, Zambia and Zimbabwe, initiated coordinated multi-country vaccination campaigns to protect all at-risk children. Thanks to the swift response, which included cross-border planning strategies, no new cases have been detected in the region since August 2022. Increased immunization efforts to reach every child, coupled with strengthened environmental surveillance, has been critical to the region's ability to halt the virus. To date, over 50 million children have been reached in multiple vaccination rounds in the affected countries since the outbreak was first declared.

Dr Matshidiso Moeti, WHO Regional Director for Africa, emphasizes the indispensable role of laboratories in the Africa region: “The laboratory network stands as a beacon of hope in our fight against polio. Their dedication and expertise are instrumental in our efforts to contain and eradicate this debilitating disease."

In the 15 months that have passed since the last confirmed WPV1 detection in Mozambique, laboratory personnel have continued to play a central role in Outbreak Response Assessments (OBRAs), actively contributing to recent assessments in countries including Ethiopia, Mozambique, Tanzania and Zambia.

“After a thorough evaluation, an independent OBRA team, which rigorously assessed various facets of the outbreak response (two in-depth field reviews and supplementary data review) has concluded that there is no evidence of ongoing WPV1 transmission in Mozambique and Malawi,” Dr Jamal Ahmed, WHO AFRO Polio Eradication Programme coordinator, confirms.

The OBRA team also reviewed the quality of the outbreak response, including overall population immunity, supplementary immunization campaigns, routine immunization coverage, surveillance systems, vaccine management practices, and community engagement levels.

The fight against polio is not over, however, as variant poliovirus circulation persists in 26 African countries, with over 200 polioviruses in 26 countries in 2024 (as of mid-August, 2024). 59% (28/47) of countries in the African Region reported polio cases in the past year. This form of polio is equally dangerous, with the capacity to invade the nervous systems of children, causing paralysis or even death.

Polio has no cure, and the only way to prevent it is through immunization. The challenge is compounded by the fact that most infections are asymptomatic. This means they are not detected by Acute Flaccid Paralysis surveillance, which actively seeks out children with signs of paralysis to identify potential cases.

As such, laboratories are not only a key surveillance tool in maintaining the region´s certification as free of indigenous wild polio, but also in detecting and tracking ongoing outbreaks of circulating variant polioviruses (cVDPVs) that persist in Africa.