An Epidemiological Cohort Study of SARS-CoV-2 and COVID-19 in German Healthcare Workers – Interim Analysis after Six Months of Follow-up
Abstract BackgroundHealthcare workers (HCWs) are at increased risk of SARS-CoV-2 infection. We assessed incidence of SARS-CoV-2 infection and COVID-19 before the roll out of COVID-19 vaccines in a cohort of HCWs in Mainz, Germany.MethodsUsing prospective observational cohort design, antibody status was assessed at baseline and every 6 weeks (±2 weeks). Daily self-reported COVID-19 symptoms were collected using a smartphone application. Symptomatic HCWs were tested using RT-PCR. We estimated symptomatic and asymptomatic SARS-CoV-2 infection rates based on two case definitions of varying sensitivity and specificity.Results3664 HCWs were enrolled with a median follow-up of 101 days. The seroprevalence of anti-SARS-CoV-2 antibodies increased from 2.7% at baseline to 3.8%, with the number of seroconversions (65) outweighing seroreversions (26) by end of follow-up. Among HCWs who seroconverted, 12 (~19%) did not report any symptoms. The estimated incidence rate was 4.5 per 1000 person-months, but none the incident cases developed severe disease. Anti-SARS-CoV-2 antibodies fell below diagnostic cut-off value in a third of those positive at baseline and in one incident case.ConclusionsWe observed increasing COVID-19 rates among HCWs during an accelerated community transmission period, with relatively lower rate of asymptomatic infections. Our findings indicate a relatively long-lasting humoral immune response following natural infection.