Safety and Immunogenicity of an mRNA-1273 Booster in Children.

Background A 2-dose mRNA-1273 primary series in children aged 6 months–5 years (25 µg) and 6–11 years (50 µg) had an acceptable safety profile and was immunogenic in the phase 2/3 KidCOVE study. We present data from KidCOVE participants who received an mRNA-1273 booster dose. Methods An mRNA-1273 booster dose (10 µg for children aged 6 months–5 years; 25 µg for children aged 6–11 years; age groups based on participant age at enrollment) was administered ≥6 months after primary series completion. The primary safety objective was the safety and reactogenicity of an mRNA-1273 booster dose. The primary immunogenicity objective was to infer efficacy of an mRNA-1273 booster dose by establishing noninferiority of neutralizing antibody (nAb) responses after a booster in children versus nAb responses observed after the mRNA-1273 primary series in young adults (18–25 years) from the pivotal efficacy study. Data were collected from March 2022 to June 2023. Results Overall, 153 (6 months–5 years) and 2519 (6–11 years) participants received an mRNA-1273 booster dose (median age at receipt of booster: 2 and 10 years, respectively). The booster dose safety profile was generally consistent with that of the primary series in children; no new safety concerns were identified. An mRNA-1273 booster dose elicited robust nAb responses against ancestral SARS-CoV-2 among children and met prespecified noninferiority success criteria versus responses observed after the primary series in young adults. Conclusions Safety and immunogenicity data support administration of an mRNA-1273 booster dose in children aged 6 months to 11 years. Clinical Trials Registration NCT04796896 (Clinicaltrials.gov). [ABSTRACT FROM AUTHOR]