Prevalence and duration of anti-SARS-CoV-2 antibodies in healthcare workers.

INTRODUCTION: Knowledge of the seroprevalence and duration of antibodies against SARS-CoV-2 was needed in the early phases of the COVID-19 pandemic and is still necessary for policy makers and healthcare professionals. This information allows us to better understand the risk of reinfection in previously infected individuals. METHODS: We investigated the prevalence and duration of detectable antibodies against SARS-CoV-2 in sequentially collected samples from 379 healthcare professionals. RESULTS: SARS-CoV-2 seroprevalence at inclusion was 5.3% (95% confidence interval (CI): 3.3-8.0%) and 25% of seropositive participants reverted during follow-up. At the end of follow-up, the calculated probability of having detectable antibodies among former seropositive participants was 72.2% (95% CI: 54.2-96.2%). CONCLUSION: Antibodies against SARS-CoV-2 were detectable in a subset of infected individuals for a minimum of 39 weeks. FUNDING: The assays performed at Rigshospitalet were developed with financial support from the Carlsberg Foundation (CF20-0045) and the Novo Nordisk Foundation (NFF205A0063505 and NNF20SA0064201). TRIAL REGISTRATION: The study was registered with the Danish National Committee on Health Research Ethics (H-20022312).