Seroprevalence of anti-SARS-CoV-2 antibodies in women attending antenatal care in eastern Ethiopia

Abstract

Information on the cumulative incidence of SARS-CoV-2 in East Africa is scarce. We conducted serosurveillance of anti-SARS-CoV-2 antibodies among pregnant women attending their first antenatal care visit in three health facilities in eastern Ethiopia. We collected questionnaire data and a blood sample from 3,312 pregnant women between April 1, 2020 and March 31, 2021 at health facilities in Haramaya, Awoday and Harar. We selected 1,447 blood samples at random and assayed these for anti-SARS-CoV-2 antibodies at Hararghe Health Research laboratory using WANTAI SARS-CoV-2 Rapid Test for total immunoglobulin. Temporal trends in seroprevalence were analysed with a X2 test for trend and multivariable binomial regression. Among 1,447 sera tested, 83 were positive for anti-SARS-CoV-2 antibodies giving a crude seroprevalence of 5.7% (95% CI 4.6%, 7.0%). Of 160 samples tested in April-May, 2020, none was seropositive; the first seropositive sample was identified in June and seroprevalence rose steadily thereafter (X2 test for trend;p=0.003) reaching a peak of 11.8% in February, 2021. In the multivariable model, seroprevalence was approximately 3% higher in first-trimester mothers compared to later presentations, and rose by 0.75% (95% CI 0.31%, 1.20%) per month of calendar time. This clinical convenience sample illustrates the dynamic of the SARS-CoV-2 epidemic in young adults in eastern Ethiopia; infection was rare before June 2020 but it spread in a linear fashion thereafter, rather than following intermittent waves, and reached 10% by the beginning of 2021. After one year of surveillance, most pregnant mothers remained susceptible.