Demographic and Clinical Factors Associated With Anti–SARS-CoV-2 Antibody Levels After 2 BNT162b2 mRNA Vaccine Doses

IMPORTANCE: The factors associated with long-term serum levels of anti–SARS-CoV-2 antibodies after COVID-19 vaccination in healthy individuals have rarely been investigated. OBJECTIVE: To investigate factors associated with anti–SARS-CoV-2 antibody levels. DESIGN, SETTING, AND PARTICIPANTS: This prospective cohort study included health care workers at Kyungpook National University Chilgok Hospital (Daegu, Korea) with no history of SARS-CoV-2 infection who received 2 doses of the BNT162b2 mRNA COVID-19 vaccine (Pfizer/BioNTech; first dose, March 17-20, 2021; second dose, April 7-10, 2021). Serum samples were collected at 2, 4, and 6 months after the second injection. INTERVENTIONS: SARS-CoV-2 BNT162b2 mRNA vaccine. MAIN OUTCOMES AND MEASURES: Anti–SARS-CoV-2 specific antibodies were measured using enzyme-linked immunosorbent assay kits up to 6 months after the receipt of 2 doses of the BNT162b2 mRNA COVID-19 vaccine. The main outcome was factors associated with anti–SARS-CoV-2 antibody levels at 6 months. RESULTS: All 50 participants (mean [SD] age, 34.7 [9.4] years; 10 [20.0%] male; mean [SD] body mass index, 21.8 [5.4]) acquired anti–SARS-CoV-2 antibodies and maintained positive antibody (cutoff ≥30%) up to 6 months. The mean serum antibody level decreased with time (91.9%, 89.3%, and 81.5% at 2, 4, and 6 months, respectively). Serum antibody levels at 6 months were correlated with antibody levels at 2 months (R = 0.944; P < .001). The anti–SARS-CoV-2–specific antibody level was inversely correlated with weight, body mass index, body fat amount, and body weight to height ratio in Spearman correlation analysis. A 1-SD increase in body weight, weight to height ratio, and body mass index was associated with a 4%- to 5%-decrease in anti–SARS-CoV-2 antibodies in multiple linear regression analysis for women. In multivariate analysis for categorized variables, lower serum level of antibody (ie, <81.5%) was associated with weight (weight ≥55 kg: odds ratio, 9.01; 95% CI, 1.44-56.40). The probabilities of less than 70% and less than 80% antibody at 6 months were 0% and 11% in participants weighing less than 55 kg, respectively, but 16% and 42% in participants weighing 55 kg or greater. CONCLUSIONS AND RELEVANCE: In this study, the inverse correlation of anti–SARS-CoV-2–specific antibody levels with weight was sustained up to 6 months after vaccination. A booster shot of BNT162b2 mRNA vaccination may be given later than 6 months after the second dose in young and middle-aged healthy persons with low body weight.