The Effect of Third Dose of Pfizer/BioNTech and Moderna COVID-19 mRNA Vaccines on IgG Antibody Titers

With the emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants, the Centers for Disease Control and Prevention (CDC) authorized the third dose of the Pfizer-BioNTech (BNT162b2) vaccine with the rationale for prolonged elevation of anti-SARS-CoV-2 antibody titers and protection against the SARS-CoV-2 virus. To better understand how administration of the third dose of the Pfizer/BioNTech coronavirus disease 2019 (COVID-19) vaccine affects the incidence and severity of SARS-CoV-2 infections, we administered the third dose of the Pfizer-BioNTech (BNT162b2) to 189 participants. Blood samples were collected from participants during each of their scheduled visits (baseline, week two, week 12, and week 24) and tested for semi-quantitative anti-SARS-CoV-2 immunoglobulin G (IgG) titers. Our results showed that administration of the third dose of the Pfizer-BioNTech (BNT162b2) vaccine elicited elevated anti-SARS-CoV-2 IgG antibodies for the 24-week duration of the study. IgG antibody titers were greatest in week two, and progressively decreased by week 12 and week 24, with statistically significant differences between the IgG antibody titers for each collection date.