Dynamics of Antibody Response to BNT162b2 mRNA COVID-19 Vaccine: A 7-Month Follow-Up Study

Background and Objectives: Comprehension regarding immunity to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is limited, and the durability of immune responses after vaccination is currently unknown. Several studies have reported on the antibody response in fully vaccinated individuals with a limited follow-up of the participants, i.e., below 7 months. Materials and Methods: The antibody response to complete vaccination with the BNT162b2 mRNA COVID-19 vaccine was assessed monthly, for 7 months, in 92 healthcare workers, between February 26 and September 26, 2021. The SARS-CoV-2 anti-spike protein IgG (IgG_S) antibody was detected using the SARS-CoV-2 IgG II Quant assay (Abbott, Diagnostics Division, Sligo, Ireland), a chemiluminescent microparticle immunoassay (CMIA) with a sensitivity of 98.1% and specificity of 99.6%. Participants were divided into two groups, one for individuals previously infected with SARS-CoV-2 and the other for individuals without previous infection. Results: The median IgG_S titers decreased monthly both in previously infected individuals and in the uninfected group. Previously infected individuals had significantly higher median titers of IgG_S compared with previously uninfected subjects at all seven time points after complete vaccination (p < 0.001). Conclusions: Seven months after vaccination, the median IgG_S titer had decreased by more than 92% both in individuals previously infected with SARS-CoV-2 and in uninfected individuals. However, IgG_S antibodies were still detected in all study participants and persisted throughout the 7 months after the second dose of the vaccine. Further studies should be conducted to monitor the antibody response to the BNT162b2 mRNA vaccine beyond 7 months, to assess the need for a new booster dose in order to extend the duration and amplitude of the specific immune response.