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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. Supplementary Information The online version contains supplementary material available at 10.1186/s12916-021-02032-2.

We determined the duration and baseline determinants of antibody responses to SARS-CoV-2 up to nine months after COVID-19 symptoms onset in 173 primary health care worker patients from Spain. Seropositivity to SARS-CoV-2 spike and RBD antigens was 92.49% (60.69% IgM, 76.3% IgA, 90.17% IgG), with four suspected reinfection cases. Antibody levels significantly correlated with fever, hospitalization, anosmia/hypogeusia, allergies, smoking and occupation, and persisted 149-270 days in this cohort of patients