Severe Acute Respiratory Syndrome Coronavirus 2 serosurveillance in a patient population reveals differences in virus exposure and antibody-mediated immunity according to host demography and healthcare setting

Identifying drivers of SARS-CoV-2 exposure and quantifying population immunity is crucial to prepare for future epidemics. We performed a serial cross-sectional serosurvey throughout the first pandemic wave among patients from the largest health board in Scotland. Screening of 7480 patient sera showed a weekly seroprevalence ranging from 0.10% to 8.23% in primary and 0.21% to 17.44% in secondary care, respectively. Neutralisation assays showed that around half of individuals who tested positive by ELISA assay, developed highly neutralising antibodies, mainly among secondary care patients. We estimated the individual probability of SARS-CoV-2 exposure and quantified associated risk factors. We show that secondary care patients, males and 45-64-year-olds exhibit a higher probability of being seropositive. The identification of risk factors and the differences in virus neutralisation activity between patient populations provided insights into the patterns of virus exposure during the first pandemic wave and shed light on what to expect in future waves