Background Longitudinal serology studies can assist in analyzing kinetics of antibodies to the SARS-CoV-2 virus, helping to inform public health decision-making. Our study aims to characterize circulating antibody trends over 18 months in vaccinated participants with and without evidence of COVID-19 infection. Methods A cohort of healthcare workers employed at Boston Medical Center were followed, collecting serum samples and survey data over six timepoints from July 2020 through December 2021 (n = 527). History of SARS-CoV-2 infection, vaccination and booster status were confirmed, where possible, using electronic medical records. Serum was assessed for the qualitative detection of anti-N IgG and the semi-quantitative detection of anti-S IgG antibody levels. Piecewise regression models were utilized to characterize the antibody kinetics overtime. Results Anti-S IgG titers remained above the positivity threshold following infection and/or vaccination throughout the 18-month follow-up. Among participants with no evidence of COVID-19 infection, titers declined significantly faster in the initial 90 days post-full vaccination (β=-0.056) from December 2020 to March 2021 compared to the decline observed following booster dose uptake (β=-0.023) (p < 0.001). Additionally, COVID-19 infection prior to vaccination significantly attenuated the decline of anti-S IgG when compared to the infection-naïve participants following vaccine uptake (p < 0.001). Lastly, fewer boosted participants contracted Omicron (12.7%) than fully vaccinated (17.6%). Among the Omicron-positive participants, anti-S IgG titers were lower, but not significantly, than those who did not test positive when comparing by vaccination status. Conclusions These findings provide novel 18-month kinetics of anti-S IgG antibodies and further highlight the durability of hybrid immunity, underlining the strong humoral response stimulated by combined infection and vaccination.
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.
Over 15-months we found that anti-spike RBD SARS-CoV-2 antibody concentrations follow different trends with combinations and permutations of COVID-19 infection and vaccination among healthcare workers in Boston, MA. A majority of HCWs remain well above the positivity threshold for anti-spike RBD IgG antibodies for at least 9 months following vaccination regardless of infection history. Of interest, 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 timepoint. These findings further support what is known regarding the decline in serum antibody concentrations following natural infection and vaccination, adding knowledge of serum antibodies up to 15 months post infection and 11 months post vaccination.ImportanceBoston Medical Center (BMC) is a safety net hospital in Boston and from the initial wave of COVID-19 there has been overwhelming concern about the exposure of healthcare workers to SARS-CoV-2. We conceived a longitudinal study to assess virus exposure and trends in SARS-CoV-2 antibodies amongst healthcare workers at BMC over 15 months. We have followed HCWs through three waves of COVID-19, including the Delta variant wave from June through mid-December 2021, assessing anti-spike receptor binding domain IgG, anti-nucleocapsid IgG, and anti-spike IgM at approximately three-month intervals. Current literature largely describes antibody durability six months post vaccination. These data add to the literature by describing antibody durability and trend differences according to infection history and vaccination status. These longitudinal data contribute to a greater understanding of the ongoing COVID-19 pandemic and can help inform future research and public health decision-making regarding vaccine uptake, breakthrough infections, and overall pandemic response.
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