Fifteen-Month Follow-Up of Anti-Spike Receptor-Binding Domain SARS-CoV-2 Antibodies among Healthcare Workers in Boston, MA

Background: Boston Medical Center (BMC) is a safety net hospital in Boston, and from the initial wave of COVID-19 there has been an overwhelming concern about the exposure of healthcare workers (HCWs) to SARS-CoV-2. Methods: We conceived a study to follow a cohort of BMC HCWs, beginning in July 2020 and continuing for 15 months, collecting survey data and serum samples at approximately 3-month intervals. Serum samples were analyzed using the Abbott Architect i2000 for SARS-CoV-2 antibodies (anti-spike1-Receptor Binding Domain IgG and anti-nucleoprotein IgG). Positive anti-n IgG results were used, in addition to reverse transcription-PCR results, for identifying cases of infection. History of COVID-19 and vaccination status were confirmed, where possible, using electronic medical records. Participants were grouped according to vaccination and infection status in September 2021 for analysis of anti-s IgG trends. Results: A majority of HCWs remain well above the positivity threshold for anti-spike IgG antibodies for up to 11 months post-vaccination and 15 months post-infection, regardless of combinations and permutations of vaccination and infection. Those with COVID-19 infection before vaccination had significantly higher median serum antibody concentrations in comparison to HCWs with no prior infection at each follow-up time point. Conclusions: These findings further support what is known regarding the decline in serum antibody concentrations following natural infection and vaccination, adding knowledge of serum antibody levels for up to 15 months post- infection and 11 months post-vaccination.