Longitudinal Protection Following Natural SARS-CoV-2 Infection and Early Vaccine Responses: Insights from a Cohort of Community Based Dental Health Care Professionals

Background: The threshold of protection for anti-SARS-CoV-2 spike glycoprotein antibodies and their longevity are not known. Interpretation of serological results in with respect to international reference material can inform this essential question. Methods: 1,507 West Midlands dental care professionals were recruited into this study in June 2020. Baseline seroprevalence of antibodies directed against the SARS-CoV-2 spike glycoprotein was determined and the cohort was followed longitudinally for 6 months until January/February 2021 through the second wave of the COVID-19 pandemic in the United Kingdom, and commencement of vaccination. Findings: Baseline seroprevalence was 16.3% in this cohort, compared to estimates in the general population of between 6-7%. Seropositivity was retained in over 70% of participants at 3 and 6-month follow up and conferred a 74% reduced risk of infection. During follow-up, no PCR-proven infections occurred in individuals with a baseline anti-SARS-CoV-2 IgG level greater than 3.69 IU/ml with respect to the World Health Organization international standard 20-136. Post-vaccination, antibody responses were more rapid and of higher magnitude in individuals with who were seropositive at baseline. Interpretation: Natural infection leads to a serological response that remains detectable in over 70% of individuals 6 months after initial sampling and 9 months from the peak of the first wave of the pandemic. This response is associated with protection from future infection. Even if serological responses wane, a single dose of the Pfizer-BioNTech vaccine is associated with an antibody response indicative of immunological memory. Funding: The Association of Clinical Biochemistry and Laboratory Medicine and The Institute for Global Innovation (IGI) of the University of Birmingham. Conflict of Interest: MTD reports personal fees from Abingdon Health, outside the submitted work. AMC isan employee of the Binding Site Group. All other authors declare no competing interests. Ethical Approval: The study was approved by the London - Camden and Kings Cross Research EthicsCommittee (reference 20/HRA/1817). All participants provided written informed consent prior to enrolment in the study.