Influence of a Heterologous (ChAdOx1-nCoV-19/BNT162b2) or Homologous (BNT162b2/BNT162b2) Vaccination Regimen on the Antibody and T Cell Response to a Third Vaccination with BNT162b2.

Emerging numbers of SARS-CoV-2 infections are currently combated with a third vaccination. Considering the different vaccination regimens used for the first two vaccine doses, we addressed whether the previous vaccination influences the immune response to the booster. Participants for this prospective study were recruited from among healthcare workers. N = 20 participants were previously vaccinated with two doses of BNT162b2, and n = 53 received a priming dose of ChAdOx1-nCoV-19 followed by a BNT162b2 dose. Participants were vaccinated with a third dose of BNT162b2 in December 2021. Antibody concentrations were determined after vaccination, and in a subset of n = 19 participants, T cell responses were evaluated. Anti-S concentrations and IFNγ production increased during the first 21 days. The choice of the first and second vaccineshad no influence on the final outcome of the booster vaccination. Before booster vaccination, antibody concentrations were lower for older participants but increased more strongly over time.