The protective effect of SARS-COV-2 antibodies in Scottish healthcare workers

Background Healthcare workers (HCW) are believed to be at increased risk of SARS-CoV-2 infection. It is 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 HCW's in Scotland (UK) from May to September 2020. The Siemens SARS-CoV-2 total antibody assay was used to establish seroprevalence in this cohort. Controls, matched for age and sex to the general local population, were studied for comparison. New infections (up to 2/12/2020) post antibody testing 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. At enrolment 300 HCW had a positive antibody test (14.5%). 11/231 control sera tested positive (4.8%). HCW therefore had an increased likelihood of a positive test (Odds ratio 3.4 95% CI 1.85–6.16, p<0.0001). Dentists were most likely to test positive. 97.3% of patients who had previously tested positive for SARS-CoV-2 by RT-PCR had positive antibodies. 18.7% had an asymptomatic infection. There were 38 new infections with SARS-CoV-2 in HCW who were previously antibody negative and one symptomatic RT-PCR positive re-infection. The presence of antibodies was therefore associated with an 85% reduced risk of re-infection with SARS-CoV-2 (HR 0.15, 95% CI 0.06 to 0.35, p=0.026).

Conclusion HCW were three times more likely to test positive for SARS-CoV-2 than the general population. Almost all infected individuals developed an antibody response which was 85% effective in protecting against re-infection with SARS-CoV-2.