PA-386 High exposure to SARS-CoV-2 in rural Southern Mozambique after 4 waves of COVID-19: community-based serosurveys

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Background In the same month the WHO declared COVID-19 a pandemic (March 2020), the first case was reported in Mozambique, and by April 2023 the country had seen four waves of COVID-19 233,334 with cumulative positive cases and 2,242 deaths. We conducted community-based serosurveys in the Manhiça district to assess the evolution of exposure after successive COVID waves. Methods Four seroepidemiology surveys separated by ~3 months were conducted between May 2021 and June 2022. In each, 1,200 individuals residing in Manhiça District were randomly selected from the Demographic Surveillance System, stratified equitably into four age groups (0–19, 20–39, 40–49, ≥60 years). Blood samples were collected and analyzed by commercial Elisa kit (Wantai) for the detection of total antibodies (IgM and IgG). Results Overall, 4,579 participants had blood samples collected, of which 3,346 were tested. The prevalence of SARS-CoV-2 antibodies increased over time from 27.6% (184/666) in serosurvey one to 63.6% (595/936) (p: <0·001) in serosurvey two, reaching 91.2% (700/768) (p: <0·001) and 91.1% (1017/1117) (p: 0·941), in the third and fourth serosurveys, respectively. Higher antibodies detection was observed among individuals aged 20–39 years in serosurveys one, three, and four (32%, 96.1% and 94.3% respectively), but age group 40 – 59 years during serosurvey two (66.8%). A high seroprevalence (85.7%; 156/182) was still observed among individuals who had not been vaccinated at the time they were enrolled in serosurvey 4. The pattern of increasing seroprevalence was related to the occurrence of COVID-19 waves. Conclusion Our data demonstrate increased seroprevalence levels after each serosurvey from 27% to 91%, showing universal exposure to SARS-CoV-2 of the general population residing in the Manhiça District after four COVID-19 waves. High seroprevalence were also observed among unvaccinated and vaccine ineligible (<18 years) individuals reaching over 90% at the last serosurvey.

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