Interim Safety and Immunogenicity of COVID-19 Omicron-BA.1 Variant-Containing Vaccine in Children

Objectives We report interim safety and immunogenicity results from a phase 3 study of omicron-BA.1 variant-containing (mRNA-1273.214) primary vaccination series (Part 1) and booster dose (Part 2) in children aged 6 months to 5 years ( NCT05436834 ). Methods In Part 1, SARS-CoV-2 unvaccinated participants, including participants who received placebo in the KidCOVE study ( NCT04796896 ), received 2 doses of mRNA-1273.214 (25-μg omicron-BA.1 and ancestral Wuhan-Hu-1 mRNA 1:1 co-formulation) primary series. In Part 2, participants who previously completed the mRNA-1273 (25-µg) primary series in KidCOVE received a mRNA-1273.214 (10-μg) booster dose. Primary objectives were safety, reactogenicity, and immunogenicity, including prespecified immune response success criteria. Results At the data cutoff (December 5, 2022), 179 participants had received ≥1 dose of mRNA-1273.214 primary series (Part 1) and 539 participants had received a mRNA-1273.214 booster dose (Part 2). The safety profile of mRNA-1273.214 primary series and booster dose was consistent with that of the mRNA-1273 primary series in this same age group, with no new safety concerns identified and no vaccine-related serious adverse events observed. Compared with neutralizing antibody responses induced by the mRNA-1273 primary series, both the mRNA-1273.214 primary series and booster elicited responses that were superior against omicron-BA.1 and non-inferior against ancestral Wuhan-Hu-1(D614G). Conclusions mRNA-1273.214 was immunogenic against BA.1 and D614G in children aged 6 months to 5 years, with a comparable safety profile to mRNA-1273, when given as a 2-dose primary series or as a booster dose after the mRNA-1273 primary series. Clinical Trial Registry NCT05436834