The exercise, which will begin in Cameroon, Chad and Niger before being extended to the Central African Republic next week, comes in response to 14 detections of type-2 poliovirus in the countries so far this year: one sample from environmental surveillance in Niger tested positive; six confirmed cases were reported in Chad; and seven in the Central African Republic.

No cases have been reported this year in Cameroon – which neighbours Chad and the Central African Republic – but the country has joined the vaccination campaign to avert any potential spread of the virus, particularly in border areas.

The multi-country initiative is supported by the World Health Organization (WHO), through the Global Polio Eradication Initiative (GPEI), and comprises synchronized vaccinations and joint plans in border communities to halt polio transmission.

“This is a crucial undertaking to close vaccination gaps in the wake of the COVID-19 pandemic and will provide millions of children with vital protection from the risk of irreversible polio paralysis,” said Dr Matshidiso Moeti, WHO Regional Director for Africa. “Synchronizing the campaign will ensure that a large cohort of children across the four countries receive the vaccine at the same time to enhance polio immunity in a broad geographic area.”

The Lake Chad region, which includes three of the four target countries, is grappling with one of the world’s most protracted incidents of armed violence. It is also home to one of the highest proportions of so-called “zero dose” children globally, who are either unvaccinated or under-vaccinated.

All the four countries have made huge efforts to bolster polio detection, curb the spread of the virus and protect children from the risk of infection and lifelong paralysis. However, despite all being certified free of indigenous wild poliovirus (the naturally circulating strain), ongoing circulating variant poliovirus type 2, the most prevalent form of polio, persists.

Across the countries, governments have continued to improve the quality of immunization activities, bolstered by the broad implementation of supplementary immunization campaigns. These are targeted at addressing the residual risks for all forms of poliovirus, while also boosting routine immunization at country level.

In addition, door-to-door implementation has eased the burden on parents to transport their children to health facilities for vaccination. Health workers, with support from WHO, are now also administering vaccines in homes, as well as at religious centres, markets and schools.

Religious and community leaders, as champions of poliovirus eradication, also help to mobilize caregivers to vaccinate their children against not only polio, but all preventable diseases.

Importantly, reliable data is crucial for effective disease surveillance and outbreak response. In the wake of the ongoing outbreaks of circulating variant poliovirus, countries have also stepped up surveillance to detect cases.

“The use of Geographic Information Systems tools, including Open Data Kit, is also accelerating the response to alerts of potential polio cases, helping curb the spread of the virus,” said Dr Richelot Ayangma, GPEI lead in West and Central Africa.

WHO, Rotary International, the United Nations Children’s Fund (UNICEF), Gavi, the Vaccine Alliance, the Bill & Melinda Gates Foundation, along with the US Centers for Disease Control and Prevention, have also joined forces behind “The Big Catch Up”. This is a targeted global effort to boost essential immunization among children following declines driven by the COVID-19 pandemic.

WHO is supporting countries on the continent to protect all children against all forms of polio.