Antibody response to second dose of the BNT162b2 mRNA vaccine in the first 12 weeks in South Korea: A prospective longitudinal study.

OBJECTIVES: To characterise the antibody response for 12 weeks following second dose of the Pfizer/BioNTech BNT162b2 mRNA vaccine in hospital workers of a Korean general hospital. METHODS: We measured the level of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) anti-receptor binding domain (anti-RBD) and neutralising antibodies every week in the first 4 weeks, and at weeks 8 and 12 following the second dose of vaccination in 71 hospital workers. RESULTS: The initial median level of anti-RBD and neutralising antibodies were 3898.0 U/mL (interquartile range [IQR], 2107.5-5478.5) and 97.54 % (IQR, 96.85-97.81), respectively. The levels declined the fastest and the most significantly between weeks 1 and 2 (p < 0.01, both), and continuously decreased thereafter, and were 1163.0 U/mL (683.4-1743.0) and 94.87% (89.24-96.99) at weeks 12. The antibodies levels showed a trend of rapid decrease in the older group over time. The slope of the decrease in the antibodies level was observed for each individual. Within 8 weeks, the anti-RBD antibody levels decreased to less than half of the initial levels in most of the participants (88.7%: 63/71). The SARS-CoV-2 anti-RBD and neutralising antibodies levels showed a strong positive correlation (Spearman's coefficient = 0.7833). CONCLUSIONS: Considerably high levels of SARS-CoV-2 anti-RBD and neutralising antibodies were produced following the second dose of vaccination. The levels decreased continuously, showing a tendency to decline over time; however, reasonable levels persisted up to weeks 12. Moreover, considering individual variations in antibody response following vaccination, a further inter-individual analysis is needed.