Disparities in anti-SARS-CoV-2 reactivity according to vaccines administered in the era of omicron in Cameroon: Lessons for future outbreak response

With the advent of COVID-19, anti-SARS-CoV-2 vaccines were a global health priority, but evidence on their significance within tropical settings remained limited. We sought to assess the distribution of anti-SARS-CoV-2 antibodies according to vaccine status and types of vaccines administered in Cameroon during Omicron waves. A community based cross-sectional sero-survey was conducted from February-15 through July-31 2022 among individuals tested for COVID-19 in Yaoundé-Cameroon. Sociodemographic data were collected from participants. Anti-SARS-CoV-2 antibodies (both IgG and IgM) were tested on plasma and statistical analyses were performed wherever appropriate. Logistic regression was done with p<0.05 considered statistically significant. Overall, 2449 participants were enrolled: median-age was 40 [31-49], 56.4% (1382/2449) men, 2.2% (54/2449) with flu-like symptoms and 19.6% (481/2449) reporting previous SARS-CoV-2 positivity. Regarding COVID-19 vaccination, 67.5% (1652/2449) had received at least one dose, 55.0% (909/1652) two-dose series and 37.1% (613/1652) received additional booster doses. Median duration from vaccination to phlebotomy was 5 [4-9] months. Seroprevalence of anti-SARS-CoV-2 antibodies was 81.1% (1987/2449). Following logistic regression, vaccine status (aOR=1.95), booster doses (aOR=1.36), post-vaccination time (≤5 months; aOR=1.64), Pfizer (aOR=2.07) and Moderna (aOR=1.52) vaccines, were all associated with a high prevalence of anti-SARS-CoV-2 antibodies (all p<0.05). This high seroprevalence of anti-SARS-CoV-2 antibodies suggests a certain degree of immunity/protection at community-level in Cameroon during Omicron waves, with Pfizer and Moderna inducing greater immunogenicity. However, rapid antibody waning (∼5 months) calls for vaccine updates with novel variants (arising from a rapidly evolving virus) that could compromise already acquired immunity.