Abstract
<title>Abstract</title> <p> During the COVID-19 pandemic, conventional surveillance systems faced critical limitations : PCR testing capacity constraints, asymptomatic transmission blind spots, and ascertainment biases skewed toward symptomatic or high-risk populations. In this context, blood donor populations emerged not merely as convenient sample sources, but as scientifically strategic epidemiological sentinels. Our objectives were to fill surveillance gaps in Niger and validate blood donors as sentinels for tracking population-level spread. A cross-sectional study was conducted from October 2021 to March 2022 among the whole population of donors attending the CNTS selected by systematic random sampling (k = 6). At all, 3656 blood donors were selected. Questionnaires collected data on socio-demographic characteristics, exposure risks to SARS-CoV-2, and prevention practices. Blood samples were analyzed for serology. Chi² and Fisher’s exact tests were used for categorical variables. Among the 3656 selected blood donors, sex ratio (M/F) was 4.1 and 12% were vaccinated with at least one dose. The overall seroprevalence of SARS-CoV-2 among vaccinated and non-vaccinated was respectively 65% and 53% (p-value < 0.01). In vaccinated group, seropositivity rate was statistically higher in more 50 years age group (87%,) and no difference was shown in non-vaccinated group (p-value = 0.54). Among vaccinated, according with blood groups, 0 <sup>−</sup> group was less positive than other groups (46%) and among unvaccinated group 0 <sup>+</sup> group was less positive than other groups (48%)). In multivariate analysis, headache and anorexia were associated to SARS-CoV-2 seropositivity. Blood donor seroprevalence studies provide an rapid, scalable, and ethically deployable surveillance necessary to track an respiratory virus with high asymptomatic carriage, make the control of virus circulation possible in healthy people and help implement strategies to reduce virus transmission. </p>