Longitudinal Serological and Vaccination Responses to SARS-COV-2 in Dental Professionals

Objectives: Background: The SARS-COV-2 (COVID-19) pandemic significantly impacted dental professionals (DPs), who are thought to be at high occupational risk of infection. Seroepidemiological studies can define DPs’ occupational risk.

Aims: To determine the magnitude, persistence and neutralising capacity of serum antibody responses to the SARS-COV-2 spike glycoprotein at baseline (3-months following first wave), 3- and 6-months in an observational cohort of UK DPs, and the IgG threshold for protection from re-infection.
Methods: 1507 participants provided baseline venous blood samples between the 3-26th June 2020. The total antibody response (combined IgG, A and M), and individual isotype response against the SARS-CoV-2 spike glycoprotein were measured. The neutralising ability of antibodies was determined using a plaque reduction micro-neutralisation assay. The minimum baseline IgG concentration associated with complete protection against PCR-proven re-infection for 6 months was determined in reference to the first WHO international reference material for SARS-CoV-2 serology.
Results: Baseline seroprevalence was 16.3%. Seropositivity was retained in 73% of participants who returned 3-months post-baseline (n=148/203) and 72% of participants who returned at 6-months, prior to their vaccination (n=57/79). 926/1507 participants returned at 6-months and reported 77 PCR-confirmed SARS-CoV-2 infections during follow-up (8.3%). Seropositivity arising following natural infection during the first wave, conferred a 74% risk reduction for re-infection during follow-up (9.6% seronegative, vs. 2.8% seropositive). No PCR proven infections arose in individuals with a baseline anti-SARS-COV-2 IgG level above 147.6 IU/ml (WHO standard 20-136). Serological responses were detectable in over 95% of Pfizer-BioNTech vaccine recipients and were quantitatively greater in those with prior evidence of SARS-CoV-2 infection.
Conclusions: Natural infection with SARS-COV-2 leads to persistent, neutralising and protective serological responses in over 70% of DPs 9-months post-infection (6-months post-baseline). We define a putative threshold of protection for anti-SARS-CoV-2 spike glycoprotein antibodies in reference to the WHO standard.