Polio, a highly infectious viral disease that can cause paralysis and even death, has resurfaced in Nigeria despite the country having become poliovirus-free in August 2020. Recent data shows that as of September 2024, health officials have recorded 70 cases of a circulating poliovirus type 2 (cVPV2) in 14 northern Nigerian states, spreading across 46 local government areas.
This poliovirus variant was discovered in Nigeria in 2021, and since then 1028 recorded cases from different sources across 31 states have been found which accounts for over 70% of cases in the African region.
This variant strain continues to circulate, particularly in high-risk regions of the country. In 2022 alone, Nigeria reported about 170 cases which was a decrease from the 2021 figure. Between January and August 2023, the authorities recorded 51 cases, with 47 of these occurring in the North-West. In 2024, health officials recorded about 50 cases between January and May and, despite multiple vaccination campaigns and monitoring efforts, the situation has not been fully contained.
According to Dr. Jamal Ahmed, Coordinator for the Polio Eradication Program at WHO’s Regional Office for Africa, this variant typically affects under-immunized communities where routine vaccine coverage is suboptimal. This allows the weakened virus in the oral polio vaccine to mutate, become transmissible, and continue to circulate among the population.
During prolonged circulation, the virus undergoes genetic changes through various mutations which can sometimes restore the virus’s ability to cause paralysis, transforming it into a circulating vaccine-derived poliovirus such as cVPV2.
He explained that the mutation of the oral polio vaccine (OPV) virus occurs when the virus replicates in a person’s gut. Each time it replicates, small genetic changes can take place. While the OPV is usually safe, in communities with low immunity, these mutations can build up over time, eventually making the virus stronger and capable of causing outbreaks.
Causes and contributing factors
According to Dr. Danjuma Nehemiah, a health specialist, the resurgence of polio variants in Nigeria is primarily due to low routine vaccination coverage, ongoing conflicts in northern regions, and poor sanitation. Between 2021 and 2024, Nigeria’s immunization coverage has shown persistent gaps, particularly for polio vaccines. The routine immunization coverage for the third dose of the polio vaccine remained stagnant at about 52-57% from 2020 to 2022, despite global recommendations to aim for at least 90% coverage. This poor level of coverage leaves many children unprotected, especially in regions like northern Nigeria, which has faced heightened challenges with low routine immunization coverage and vaccine hesitancy among members of the communities.
Factors such as limited access to health facilities in war zones and misconceptions about immunizations continue to contribute to low adoption. Conflict and instability in northern Nigeria have also made it exceedingly difficult for health professionals to conduct immunization programs. Armed gangs and bandits operate in these regions, limiting access to communities and disrupting normal immunization attempts. According to WHO experts, the ongoing conflict makes it dangerous for healthcare workers to travel or set up vaccination sites.
These conditions allow the weakened OPV virus to circulate in communities for longer periods, increasing the risk of mutation into the more dangerous vaccine-derived poliovirus.
Contaminated water, the lack of toilet facilities, and dense living conditions then make it highly transmissible, especially in communities using shared or untreated water sources.
Response and interventions
In response to the resurgence, the Katsina State administration, in collaboration with WHO and the Bill and Melinda Gates Foundation, has modified its immunization programs to ensure that all vulnerable children receive potentially life-saving vaccines.
Interventions, such as identifying, training, and deploying local volunteers as champions and vaccinators through traditional leaders, have proven to be extremely beneficial. As of June 2024, the Katsina local response team had vaccinated 253,006 targeted children from 11 local governments, out of a total of 326,069 children.
