The Seroprevalence and Protective Effect of SARS-COV-2 Antibodies in Scottish Healthcare Workers

Abstract

RATIONALE: Healthcare workers (HCW) are believed to be at increased risk of SARS-CoV-2 infection. The extent of that increased risk compared to the general population and the groups most at risk have not been extensively studied. It is also not known to what extent the natural production of antibodies to SARS-CoV-2 is protective against re-infection. Methods: A prospective observational study of health and social care workers in NHS Tayside (Scotland, UK) from May to September 2020. The Siemens SARS-CoV-2 total antibody assay was used to establish seroprevalence in this cohort. Patients provided clinical information including demographics and workplace. Controls, matched for age and sex to the general Tayside population, were studied for comparison. New laboratory confirmed infections post September 2020 were recorded to determine if the presence of SARS-CoV-2 antibodies protect against re-infection. Results: A total of 2063 health and social care workers were recruited for this study. The participants were predominantly female (81.7%) and 95.5% were white. 300 healthcare workers had a positive antibody test (14.5%). 11 out of 231 control sera tested positive (4.8%). Healthcare workers therefore had an increased likelihood of a positive test (Odds ratio 3.4 95% CI 1.85-6.16, p<0.0001). Dentists, healthcare assistants and porters were the job roles most likely to test positive. Those working in front-line roles with COVID-19 patients were more likely to test positive (17.4% vs. 13.4%, p=0.02). 97.3% of patients who had previously tested positive for SARSCoV-2 by RT-PCR had positive antibodies, compared to 10.9% of individuals with a symptomatic illness who had tested negative. 18.7% of HCW had an asymptomatic infection. Anosmia was the symptom most associated with the presence of detectable antibodies. There were 38 new infections with SARS-CoV-2 in HCW who were previously antibody negative and 1 symptomatic RT-PCR positive re-infection in a HCW who had detectable antibodies 76 days prior to re-infection. The presence of antibodies was 85% protective against re-infection with SARS-CoV-2 (HR 0.15, 95% CI 0.06 to 0.35, p=0.03). Conclusion: In this study, healthcare workers were three times more likely to test positive for SARS-CoV-2 than the general population. Almost all of the infected individuals developed an antibody response and this was 85% effective in protecting against reinfection with SARS-CoV-2.