High immunity and low mortality after Omicron and mass event in Cameroon despite low vaccination.

BACKGROUND

Little is known about the evolution of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) immunity in African communities.

AIM

We evaluated changes in anti-SARS-CoV-2 antibodies, mortality and vaccination status in Cameroon between August 2021 and September 2022 to begin describing the evolution of the pandemic in Africa.

SETTING

The study was conducted across Cameroon's 10 regional capitals, between 2021 and 2022 as the country hosted a mass gathering.

METHODS

We conducted a cross-sectional population-based survey in 2022, including SARS-CoV-2 seroprevalence testing and retrospective mortality estimation using two-stage cluster sampling. We estimated and compared seroprevalence and crude mortality rates (CMR) to a survey conducted in 2021 using the same methodology.

RESULTS

We performed serologic testing on 8400 individuals and collected mortality data from 22 314 individuals. Approximately 5% in each survey reported SARS-CoV-2-vaccination. Rapid diagnostic test-based seroprevalence increased from 11.2% (95% confidence interval [CI]: 10-12.5) to 59.8% (95% CI: 58.3-61.2) between 2021 and 2022, despite no increase in the proportion vaccinated. The CMR decreased from 0.17 to 0.06 deaths per 10 000 persons per day between 2021 and 2022. In 2022, no deaths were reportedly attributable to COVID-19 as compared to 17 deaths in 2021.

CONCLUSION

Over a 12-month period encompassing two waves of omicron variant SARS-CoV-2 and a mass gathering, SARS-CoV-2 seropositivity in Cameroon approached 60%, and deaths declined despite low vaccination coverage.

CONTRIBUTION

This study challenges the assumption that high immunisation coverage is the sole determinant of epidemic control in the African context and encourages policymakers to increasingly rely on local research when designing response strategies for more effective outbreak management.