Comparing immunogenicity and efficacy of two different mRNA-based COVID-19 vaccines as a fourth dose; six-month follow-up, Israel, 27 December 2021 to 24 July 2022

We assess the immunogenicity and efficacy of Spikevax and Comirnaty as fourth dose COVID-19 vaccines. Six months post-fourth-dose, lgG levels were higher than pre-fourth dose at 1.58-fold (95°/o CI: 1.27-1.97) in Spikevax and 1.16-fold (95°/o CI: 0.98- 1.37) in Comirnaty vaccinees. Nearly 60% (159/274) of vaccinees contracted SARS-CoV-2. lnfection hazard ratios (HRs) for Spikevax(o.82; 95% CI: 0.62-1.09) and Comirnaty ;68.ס(95% Cl:0.65-1.13) vaccinees were similar, as were substantial-disease HRs, i.e. 0.28 (95% CI: 0.13-0.62) and 0.51 (95% CI: 0.27-0.96), respectively.