ABSTRACT
OBJECTIVES: To assess safety and immunogenicity of a 4th vaccination (2nd booster) in individuals ≥75 years METHODS: Participants were randomised to BNT162b2 (Comirnaty®, 30µg) or mRNA-1273 (Spikevax®, 100µg). The primary endpoint was the rate of 2-fold antibody titre increase 14 days post-vaccination targeting the receptor binding domain (RBD) region of wild-type SARS-CoV-2. Secondary endpoints included changes in neutralising activity against wild-type and 25 variants. Safety was assessed by monitoring solicited adverse events (AE) for seven days. RESULTS: 269 participants (mean age 81 years, mRNA-1273 n=135/BNT162b2 n=134) were included. 2-fold anti-RBD IgG titre increase was achieved by 101/129 (78%) and 116/133 (87%) subjects in the BNT162b2 and the mRNA-1273 group, respectively (p=0.054). A 2nd booster of mRNA-1273 provided higher anti-RBD IgG geometric mean titre: 21.326 IU/mL (95%-CI: 18.235; 24.940) vs. BNT162b2: 15.181 IU/mL (95%-CI: 13.172; 17.497). Higher neutralising activity was noted for the mRNA-1273 group. The most frequent AE was pain at injection site (51% in mRNA-1273 and 48% in BNT162b2). Participants in the mRNA-1273 group had less vaccine-related AEs (30% vs. 39%). CONCLUSIONS: A 2nd booster of either BNT162b2 or mRNA-1273 provided substantial IgG increase. Full-dose mRNA-1273 provided higher IGG levels and neutralising capacity against SARS-CoV-2 with similar safety profile for subjects of advanced age.
