Correlation between Anti-SARS-CoV-2 Total Antibodies and Spike Trimeric IgG after BNT162b2 Booster Immunization

Objective: In this work we monitored both total and IgG anti-SARS-CoV-2 antibodies responses after BNT162b2 vaccine booster immunization in a cohort of ostensibly healthy healthcare workers. Methods: The study population consisted of 266 subjects (median age, 46 years and interquartile range (IQR), 35–52 years; 168 females) undergoing homologous 30-µg BNT162b2 booster administration. Serum samples were collected immediately before the booster dose and 1 month after. Results: The concentration of anti-SARS-CoV-2 RBD total antibodies and anti-SARS-CoV-2 spike trimeric IgG increased by 31 (IQR, 16–53) and 22 (IQR, 11–43) folds, respectively, after receiving the BNT162b2 vaccine booster. A highly significant Spearman′s correlation was found between the relative increase (i.e., ratio of post-booster and pre-booster serum values) of anti-SARS-CoV-2 RBD total antibodies and anti-SARS-CoV-2 spike trimeric IgG (r = 0.86; p < 0.001). Conclusion: These results suggest that monitoring of post-BNT162b2 booster immunization for purposes of identifying “low responders” could be conducted almost interchangeably with either total or IgG anti-SARS-CoV-2 antibodies.