Epidemiology of natural immunity against COVID-19 in Benin

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Abstract
This study aimed to determine the national seroprevalence of natural immunity against COVID-19 in Benin and to identify factors associated with prior SARS-CoV-2 infection. A descriptive and analytical cross-sectional study was conducted between April and September 2023 across all 12 departments of Benin. A total of 3,802 participants were recruited using convenience sampling from selected health facilities, ensuring broad geographic representation of the population.Natural immunity was differentiated from vaccine-induced immunity through enzyme-linked immunosorbent assay (ELISA) testing for anti-nucleocapsid (NCP) IgG and anti-spike (S) IgG antibodies. The overall seroprevalence of natural immunity was estimated at 38.58% (95% CI: 37.0–40.1), indicating substantial exposure to SARS-CoV-2 nationwide. Despite this high seroprevalence, only 5% of participants reported a known history of COVID-19 infection, compared with approximately 10% among individuals with evidence of immunization, highlighting a large proportion of undiagnosed or asymptomatic infections.Multivariate logistic regression analysis identified several factors independently associated with natural immunity. These included increasing age (adjusted odds ratio [aOR] = 1.56; p = 0.01), residence within the former sanitary cordon (aOR = 1.34; p = 0.006), a history of hypertension or other cardiovascular diseases (aOR = 3.25; p < 0.001), and diabetes (aOR = 2.73; p < 0.001). The findings confirm significant and largely silent circulation of SARS-CoV-2 in Benin. The strong association between natural immunity and non-communicable diseases underscores the need for targeted vaccination strategies, improved risk communication, and strengthened surveillance systems, particularly for vulnerable populations in Benin and the wider West African region. Keywords: SARS-CoV-2; Natural Immunity; Seroprevalence; Comorbidities; Benin.

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