Short-Term Drop in Antibody Titer after the Third Dose of SARS-CoV-2 BNT162b2 Vaccine in Adults

Little is known about the longevity of antibodies after a third dose of the mRNA-based SARS-CoV-2 vaccine BNT162b2 (BioNTech/Pfizer, Mainz, Germany). Therefore, serum antibody levels were evaluated after a third dose of BNT162b2 in healthy adult healthcare workers in Germany. These antibody levels dropped significantly within a short period of 11 weeks from 4155.59 ± 2373.65 BAU/mL to 2389.10 ± 1433.90 BAU/mL, p-value < 0.001 but remained higher than after the second dose (611.92 ± 450.31 BAU/mL). To evaluate the quality of the humoral immune response, we additionally measured neutralizing antibodies, which also showed a small but significant decrease within this short period. These data underline the positive effect of a third dose of BNT162b2 concerning antibody re-induction but also shows a drop of Anti-SARS-CoV-2-IgG within a short span of time.