Serosurveillance after a COVID‐19 vaccine campaign in a Swiss police cohort

Abstract Introduction To assess the risk for COVID‐19 of police officers, we are studying the seroprevalence in a cohort. The baseline cross‐sectional investigation was performed before a vaccination campaign in January/February 2021, and demonstrated a seroprevalence of 12.9%. Here, we demonstrate serosurveillance results after a vaccination campaign. Methods The cohort consists of 1022 study participants. The 3‐ and 6‐month follow‐up visits were performed in April/May and September 2021. Data on infection and vaccination rates were obtained via measuring antibodies to the nucleocapsid protein and spike protein and online questionnaires. Results The mean age of the population was 41 (SD 8.8) years, 72% were male and 76% had no comorbidity. Seroconversion was identified in 1.05% of the study population at the 3‐month visit and in 0.73% at the 6‐month visit, resulting in an infection rate of 1.8% over a time period of 6 months. In comparison, the infection rate in the general population over the same time period was higher (3.18%, p = .018). At the 6‐month visit, 77.8% of participants reported being vaccinated once and 70.5% twice; 81% had an anti‐S antibody titer of >250 U/ml and 87.1% of ≥2 U/ml. No significant association between infection and job role within the department, working region, or years of experience in the job was found. Anti‐spike antibody titers of vaccinated study participants showed a calculated decreasing trend 150–200 days after the second vaccine dose. Conclusion These data confirm the value of the vaccination campaign in an exposed group other than healthcare professionals.