Abstract
Objective: To investigate the reactogenicity and immunogenicity of the fourth dose mRNA vaccines after different three-dose regimens, followed by a comparison between the 30 μg BNT162b2 and 50 μg mRNA-1273 groups. Methods: The prospective cohort study was performed between June and October 2022. The self-recorded reactogenicity after 7 subsequent days following a fourth booster dose was evaluated. The binding antibodies and neutralizing activity to the Omicron BA.4/5 variants were determined. Results: Overall, 292 healthy adults were enrolled and received either the BNT162b2 or mRNA-1273. The reactogenicity was mild to moderate and well-tolerated within a few days. Sixty-five individuals were excluded. A total of 227 eligible individuals received the fourth booster dose of BNT162b2 (n=109) and mRNA-1273 (n=118). Most participants, regardless of different previous three dose regimens, significantly elicited a high level of binding antibody and neutralizing activity against the Omicron BA.4/5 at 28 days after a fourth dose. The neutralizing activity against the Omicron BA.4/5 between the BNT162b2 (82.8%) and mRNA-1273 (84.2%) groups was comparable with a median ratio of 1.02. Conclusion: The findings indicated that the BNT162b2 and mRNA-1273 can be used as a fourth booster dose for individuals who were previously immunized with any mix-and-match three-dose COVID-19 vaccine.
