Background Protests and police fieldwork provides a high exposure environment for SARS-CoV-2 infections. In this cross-sectional analysis, we investigated the seroprevalence among a police cohort, and sociodemographic, work and health-related factors associated with seropositivity. Methods Study participants were invited for serological testing of SARS-CoV-2 and to complete online questionnaires. Serum neutralization titres towards the wild-type SARS-CoV-2 spike protein (expressing D614G) and the alpha and beta variants were measured in seropositive study participants. Results 978 police personnel representing 35% of the entire staff participated from February to March 2021. The seroprevalence was 12.9%. It varied by geographic region within the canton; ranged from 9% to 13.5% in three regions, including the city; and was 22% in Bernese Seeland/Jura with higher odds for seropositivity (OR 2.38, 95% CI 1.28–4.44, P=0.006). Job roles with mainly office activity were associated with a lower risk of seropositivity (0.33, 0.14–0.77, P=0.010). Most seropositive employees (67.5%) reported having had COVID-19 three months or longer prior to serological testing. Selfreported compliance with mask wearing during working hours was 100%; 45% of all seropositive versus 5% of all seronegative participants (P<0.001) reported having had contact with a proven COVID-19 case living in the same household prior to serological testing. The level of serum antibody titres correlated with neutralization capacity. Antibodies derived from natural SARS-CoV-2 infection effectively neutralized the SARS-CoV-2 spike protein, but were less effective against the alpha and beta variants. Conclusions The seroprevalence of anti-SARS-CoV-2 antibodies of police officers was comparable to that reported in the general population, suggesting that the personal protective equipment of the police is effective, and that household contacts are the leading transmission venues. The level of serum antibody titres, in particular that of anti-spike antibodies, correlated well with neutralization capacity. Low antibody titres acquired from natural infection were not effective against variants.

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OBJECTIVE: To determine the seroprevalence of SARS-CoV-2 antibodies in employees of the Cantonal Police Bern, Switzerland; to investigate individual and work-related factors associated with seropositivity; and to assess the neutralizing capacity of the antibodies of seropositive study participants. DESIGN: Cross-sectional analysis of a cohort study. SETTING: Wearing face masks was made mandatory for employees of the police during working hours at the rise of the second wave of the pandemic in mid-October 2020. Protests and police fieldwork provided a high exposure environment for SARS-CoV-2 infections. The investigation was performed prior to initiation of a vaccine programme. Study participants were invited for serological testing of SARS-CoV-2 and to complete questionnaires on sociodemographic, work and health-related questions. PARTICIPANTS: 978 police personnel working in four different geographic districts, representing 35% of the entire staff, participated from February to March 2021. MAIN OUTCOME MEASURES: Seroprevalence of anti-SARS-CoV-2 antibodies in February to March 2021, geographic and work-related risk factors for seropositivity, and serum neutralization titres towards the wild-type SARS-CoV-2 spike protein (expressing D614G) and the alpha and beta variants. RESULTS: Seroprevalence was 12.9% (126 of 978 employees). It varied by geographic region within the canton; ranged from 9% to 13% in three regions, including the city; and was 22% in Bernese Seeland/Jura. Working in the latter region was associated with higher odds for seropositivity (odds ratio 2.38, 95% confidence interval 1.28 to 4.44, P=0.006). Job roles with mainly office activity were associated with a lower risk of seropositivity (0.33, 0.14 to 0.77, P=0.010). Most seropositive employees (67.5%) reported having had coronavirus disease 2019 (COVID-19) 3 months or longer prior to serological testing, and the proportion of agreement between positive nasopharyngeal test results and seroconversion was 95% to 97%. Among reported symptoms, new loss of smell or taste was the best discriminator for seropositivity (odds ratio 52.4, 30.9 to 89.0, P<0.001). Compliance with mask wearing during working hours was 100%, and 45% of all seropositive versus 5% of all seronegative participants (P<0.001) reported having had contact with a proven COVID-19 case living in the same household. The level of serum antibody titres correlated well with neutralization capacity. Antibodies derived from natural SARS-CoV-2 infection effectively neutralized the SARS-CoV-2 spike protein (expressing D614G), but were less effective against the alpha and beta variants. A regression model demonstrated that anti-spike antibodies had higher odds for neutralization than did anti-nucleocapsid protein antibodies. CONCLUSIONS: Seroprevalence in the pre-vaccinated police cohort was similar to that reported in the general population living in the same region. The high compliance with mask wearing and the low proportion of seroconversion after contact with a presumed or proven COVID-19 case during working hours imply that personal protective equipment is effective and that household contacts are the leading transmission venues. The level of serum antibody titres, in particular that of anti-spike antibodies, correlated well with neutralization capacity. Low antibody titres were not effective against the alpha and beta variants.