ABSTRACT
Objectives: In a COVID-19 sero-surveillance cohort study with predominantly healthy and vaccinated individuals, the objectives were (i) to investigate longitudinally the factors associated with the quantitative dynamics of anti-spike IgG antibody levels, (ii) to evaluate whether the antibody levels were associated with protection from SARS-CoV-2 infection and (iii) to assess whether the association was different in the pre-Omicron compared with the Omicron period. Methods: The QuantiVac Euroimmun ELISA test was used to quantify anti-S1 IgG levels. The entire study period (16 months), the 11-month pre-Omicron period and the cross-sectional analysis prior to the Omicron surge included 3219, 2310 and 895 reactive serum samples from 949, 919 and 895 study participants, respectively. Mixed-effect linear, mixed-effect time-to-event and logistic regression models were used to achieve the objectives. Results: Age and time since infection or vaccination were the only factors associated with a decline of anti-S1 IgG levels. Antibody levels were significantly associated with protection from SARS-CoV-2 infection, and the association was higher for the Omicron than for the Alpha and Delta variants. In a prediction model, it was estimated that >8000 BAU/mL anti-S1 IgG was required to reduce the risk of infection with Omicron variants by 20% to 30% for 90 days. Conclusions: Anti-S1 IgG antibody levels are associated with protection from infection. The levels in the pre-Omicron periods were less significant than during the Omicron surge, which in turn required very high levels for protection in a statistical model.
Subject(s)
COVID-19ABSTRACT
OBJECTIVETo 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. DESIGNCross-sectional analysis of a cohort study. SETTINGWearing 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. PARTICIPANTS978 police personnel working in four different geographic districts, representing 35% of the entire staff, participated from February to March 2021. MAIN OUTCOME MEASURESSeroprevalence 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. RESULTSSeroprevalence 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. CONCLUSIONSSeroprevalence 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. SUMMARY BOXESO_ST_ABSWHAT IS ALREADY KNOWN ON THIS TOPICC_ST_ABSO_LIThe seroprevalence of anti-SARS-CoV-2 antibodies in the general population shows variations, depending on the geographic location of investigated study participants. C_LIO_LISocial distancing by avoiding crowds and maintaining a distance of 6 feet from others when in public are recommended. These recommendations are not realistic for security personnel and employees of a police department. C_LIO_LIPreventive strategies for individuals in a health care setting are warranted and effective to reduce potential exposures. The effect of preventive strategies on individuals working for the police force has not been investigated. C_LI WHAT THIS STUDY ADDSO_LIThe study suggests that the overall seroprevalence of anti-SARS-CoV-2 antibodies among police officers is not higher than that in the general population, despite presumed higher exposure (e.g., public protests). C_LIO_LICompliance with use of personal protective equipment among police officers was very high. The study results suggested that household contacts, rather than exposure during working hours, is the main source for viral transmission. C_LIO_LIAnti-SARS-CoV-2 antibodies derived from natural infection demonstrated good neutralization capacity towards strains that epidemiologically likely caused the infection, but moderate to poor neutralization capacity towards the alpha and beta variant. C_LI