ABSTRACT
Background The correlates of protection against SARS-CoV-2 and their longevity remain unclear. Studies in severely ill individuals have identified robust cellular and humoral immune responses against the virus. Asymptomatic infection with SARS-CoV-2 has also been described, but it is unknown whether this is sufficient to produce antibody responses. Methods We performed a cross-sectional study recruiting 554 health care workers from University Hospitals Birmingham NHS Foundation Trust who were at work and asymptomatic. Participants were tested for current infection with SARS-CoV-2 by nasopharyngeal swab for real-time polymerase chain reaction and for seroconversion by the measurement of anti-SARS-CoV-2 spike glycoprotein antibodies by enzyme linked immunosorbent assay. Results were interpreted in the context of previous, self-reported symptoms of illness consistent with COVID-19. Results The point prevalence of infection with SARS-CoV-2, determined by the detection of SARS-CoV-2 RNA on nasopharnygeal swab was 2.39% (n=13/544). Serum was available on 516 participants. The overall rate of seroconversion in the cohort was 24.4% (n=126/516). Individuals who had previously experienced a symptomatic illness consistent with COVID-19 had significantly greater seroconversion rates than those who had remained asymptomatic (37.5% vs 17.1%, {chi}2 =21.1034, p<0.0001). In the week preceding peak COVID-19-related mortality at UHBFT, seroconversion rates amongst those who were suffering from symptomatic illnesses peaked at 77.8%. Prior symptomatic illness generated quantitatively higher antibody responses than asymptomatic seroconversion. Seroconversion rates were highest amongst those working in housekeeping (34.5%), acute medicine (33.3%) and general internal medicine (30.3%) with lower rates observed in participants working in intensive care (14.8%) and emergency medicine (13.3%). Conclusions In a large cross-sectional seroprevalence study of health-care workers, we demonstrate that asymptomatic seroconversion occurs, however prior symptomatic illness is associated with quantitatively higher antibody responses. The identification that the potential for seroconversion in health-care workers can associate differentially with certain hospital departments may inform future infection control and occupational health practices.