kinetics of anti-SARS-CoV-2 antibodies over time. Results of 10 month follow up in over 300 seropositive Health Care Workers

•More than 75% HCW maintained seropositivity against SARS-CoV-2 after 9 months.•Two distinct antibody dynamic profiles were observed: declining vs. stable.•Factors associated with stable profile were age, higher baseline-titers and high-exposure to COVID-19.•Estimated mean time to loss antibodies was 375 days from baseline. The kinetics of the antibodies against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) needs to be evaluated since long-term duration of antibody remains largely unknown, particularly in infected healthcare workers (HCW). Prospective study, evaluating the longitudinal profile of anti-SARS-CoV-2 antibody titers in a random sample of 331 seropositive healthcare workers (HCW) of Spanish Hospitals Group. Serial measurements of serum IgG-anti-SARS-CoV-2 were obtained at baseline (April-May,2020), and in 2 follow-up visits. Linear mixed models were used to investigate antibody kinetics and associated factors. A total of 306 seropositive subjects (median age: 44.7years;69.9% female) were included in the final analysis. After a median follow-up of 274 days between baseline and final measurement, 235(76.8%) maintained seropositivity. Antibody titers decreased in 82.0%, while remained stable in 13.1%. Factors associated with stability of antibodies over time included age≥45 years, higher baseline titers, severe/moderate infection and high-grade exposure to COVID-19 patients. In declining profile, estimated mean antibody half-life was 146.3 days(95%CI:138.6–154.9) from baseline. Multivariate models show independent longer durability of antibodies in HCW with high-risk exposure to COVID-19 patients (+14.1 days;95%CI:0.6–40.2) and with symptomatic COVID-19 (+14.1 days;95%CI:0.9–43.0). The estimated mean time to loss antibodies was 375(95% CI:342–408) days from baseline. We present the first study measuring the kinetics of antibody response against SARS-CoV-2 in HCW beyond 6 months. Most participants remained seropositive after 9 months but presented a significant decline in antibody-titers. Two distinct antibody dynamic profiles were observed (declining vs. stable). Independent factors associated with longer durability of antibodies were symptomatic infection and higher exposure to COVID-19 patients.