Longitudinal humoral antibody response to SARS-CoV-2 infection among healthcare workers in a New York City hospital

Objective: Dynamics of humoral immune responses to SARS-CoV-2 antigens following infection suggest an initial decay of antibody followed by subsequent stabilisation. We aim to understand the longitudinal humoral responses to SARS-CoV-2 nucleocapsid (N) protein and spike (S) protein and to evaluate their correlation to clinical symptoms among healthcare workers (HCWs).

Design: A prospective longitudinal study.

Setting: This study was conducted in a New York City public hospital in the South Bronx, New York.

Participants: HCWs participated in phase 1 (N=500) and were followed up 4 months later in phase 2 (N=178) of the study. They underwent SARS-CoV-2 PCR and serology testing for N and S protein antibodies, in addition to completion of an online survey in both phases. Analysis was performed on the 178 participants who participated in both phases of the study.

Primary outcome measure: Evaluate longitudinal humoral responses to viral N (qualitative serology testing) and S protein (quantitative Mount Sinai Health System ELISA to detect receptor-binding domain and full-length S reactive antibodies) by measuring rate of decay.

Results: Anti-N antibody positivity was 27% and anti-S positivity was 28% in phase 1. In phase 1, anti-S titres were higher in symptomatic (6754 (5177-8812)) than in asymptomatic positive subjects (5803 (2825-11 920)). Marginally higher titres (2382 (1494-3797)) were seen in asymptomatic compared with the symptomatic positive subgroup (2198 (1753-2755)) in phase 2. A positive correlation was noted between age (R=0.269, p<0.01), number (R=0.310, p<0.01) and duration of symptoms (R=0.434, p<0.01), and phase 1 anti-S antibody titre. A strong correlation (R=0.898, p<0.001) was observed between phase 1 titres and decay of anti-S antibody titres between the two phases. Significant correlation with rate of decay was also noted with fever (R=0.428, p<0.001), gastrointestinal symptoms (R=0.340, p<0.05), and total number (R=0.357, p<0.01) and duration of COVID-19 symptoms (R=0.469, p<0.001).

Conclusions: Higher initial anti-S antibody titres were associated with larger number and longer duration of symptoms as well as a faster decay between the two time points.