Nationwide retrospective mortality and seroprevalence of SARS-CoV-2 antibodies in Cameroon

Background: Although the first year of the COVID-19 pandemic in Africa did not produce the expected catastrophe, the true impact of COVID-19 in the Cameroonian population was unclear. We therefore assessed the seroprevalence of anti-SARS-CoV-2 antibodies and retrospective mortality in a representative sample of the general population in the 10 administrative regions of Cameroon more than one year after the first confirmed cases of COVID-19 in these regions. We aimed to assess the extent of SARS-COV-2 infection and to detect potential increases in the crude mortality rate (CMR) during the SARS-COV-2 pandemic phase. Methods: We assessed retrospective mortality and seroprevalence of anti-SARS-CoV-2 antibodies in the 10 capital cities of Cameroon using representative samples of the general population. The study included nested anti-SARS-CoV-2 antibody prevalence surveys and retrospective mortality surveys and was conducted between 27 July 2021 and 31 August 2021. To further analyze crude mortality rates by age group and COVID wave, pre-pandemic and pandemic periods were stratified. Both laboratory-based assays (ELFA) and rapid diagnostic tests (RDT) were used to measure anti-SARS-CoV-2 seroprevalence. Results: The crude mortality rate (CMR) increased from 0.06 deaths per 10 000 persons per day (pre-pandemic) to 0.17 deaths per 10 000 persons per day (pandemic). The increase in CMR was more pronounced in people aged 20-35 years (pre-pandemic 0.02 deaths per 10 000 persons per day; pandemic 0.06 deaths per 10 000 persons per day). The estimated seroprevalence among unvaccinated persons was 9.5 % (RDT) and 15.4 % (laboratory-based). Conclusion: The seroprevalence results showed that cases were significantly underdetected by the national surveillance systems.