Persistence and baseline determinants of seropositivity and reinfection rates in health care workers up to 12.5 months after COVID-19

Abstract

We assessed the duration and baseline determinants of antibody responses to SARS-CoV-2 spike antigens and the occurrence of reinfections in a prospective cohort of 173 Spanish primary health care worker patients followed initially for 9 months and subsequently up to 12.5 months after COVID-19 symptoms onset. Seropositivity to SARS-CoV-2 spike and receptor-binding domain antigens up to 149-270 days was 92.49% (90.17% IgG, 76.3% IgA, 60.69% IgM). In a subset of 64 health care workers who had not yet been vaccinated by April 2021, seropositivity was 96.88% (95.31% IgG, 82.81% IgA) up to 322-379 days post symptoms onset. Four suspected reinfections were detected by passive case detection, two among seronegative individuals (5 and 7 months after the first episode), and one low antibody responder. Antibody levels significantly correlated with fever, hospitalization, anosmia/hypogeusia, allergies, smoking, and occupation. Stable sustainment of IgG responses raises hope for long-lasting COVID-19 vaccine immunity.

Keywords: Antibodies; Baseline determinants; COVID-19; Cohort; Duration; Health care workers; Kinetics; Reinfection; SARS-CoV-2; Spike antigen.

Fig. 1

SARS-CoV-2 antibody levels by days since COVID-19 symptoms onset. IgA, IgG, and IgM levels are represented in log₁₀ median fluorescence intensity (log₁₀ MFI). Black dots represent seropositive individuals, and gray dots represent seronegative individuals. Paired samples are joined by gray lines (continuous lines in seropositive and dashed lines in seronegative). The blue solid line represents the fitted curve calculated using the linear model method. Shaded areas represent 95% confidence intervals