AbstractBackgroundFactors influencing SARS‐CoV‐2 antibody dynamics, transmission, waning and long COVID‐19 symptomatology are still not fully understood.MethodsIn the Danish section of the Novo Nordisk Group, we performed a prospective seroepidemiological study during the first and second waves of the COVID‐19 pandemic. All employees and their household members (>18 years) were invited to participate in a baseline (June–August 2020), 6‐month follow‐up (December 2020–January 2021), and 12‐month follow‐up (August 2021) sampling. In total, 18,614 accepted and provided at least one blood sample and completed a questionnaire regarding socioeconomic background, health status, previous SARS‐CoV‐2 infection, and persistent symptoms. Total antibody and specific IgM, IgG and IgA levels against recombinant receptor binding domain were tested.ResultsAt baseline, the SARS‐CoV‐2‐antibody seroprevalence was 3.9%. At 6‐month follow‐up, the seroprevalence was 9.1%, while at 12‐month follow‐up, the seroprevalence was 94.4% (after the vaccine roll‐out). Male sex and younger age (18–40 years) were significant risk factors for seropositivity. From baseline to the 6‐month sampling, we observed a substantial waning of IgM, IgG and IgA levels (p < 0.001), regardless of age, sex and initial antibody level. An increased antibody level was found in individuals infected prior to vaccination compared to vaccinated infection naïves (p < 0.0001). Approximately a third of the seropositive individuals reported one or more persistent COVID‐19 symptoms, with anosmia and/or ageusia (17.5%) and fatigue (15.3%) being the most prevalent.ConclusionThe study provides a comprehensive insight into SARS‐CoV‐2 antibody seroprevalence following infection and vaccination, waning, persistent COVID‐19 symptomatology and risk factors for seropositivity in large working environments.