Abstract
BACKGROUND: Cell-mediated immunity (CMI) may help protect against emerging severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants that are less susceptible to neutralizing antibodies. We present CMI data after the mRNA-1273 primary series in a subset of participants aged 6 months to 11 years from the phase 2/3 KidCOVE trial. METHODS: T-cell responses were assessed after 2 doses of mRNA-1273 (6 months to 5 years, 25 μg; 6-11 years, 50 μg) or placebo administered 28 days apart. Magnitude, phenotype, and percentage of ancestral SARS-CoV-2 spike (S) protein T-cell responses to pooled peptides were assessed by intracellular cytokine staining and polyfunctionality analyses. RESULTS: A total of 68 children aged 6 months to 11 years received either the 2-dose mRNA-1273 primary series or placebo (51 and 17, respectively) at 28-day interval. mRNA-1273 induced S-protein-specific CD4+ T-cell responses exhibiting a type 1 T helper (Th1)-biased profile at day 43 and day 209 compared with placebo. S-protein-specific CD8+ T-cell responses were less frequently detected in children <5 years and undetectable in those <2 years. Compared with placebo, mRNA-1273 induced higher frequencies of S-specific polyfunctional CD4+ T cells at day 43; frequencies declined but remained detectable at day 209. Correlation between Th1 CD4+ responses and neutralizing antibodies was observed across age groups following mRNA-1273 vaccination. CONCLUSIONS: The 2-dose mRNA-1273 primary series elicited robust and durable (≥ 6 months) Th1-biased CD4+ T-cell responses in children aged 6 months to 11 years. CD8+ T-cell responses varied by age. Clinical Trials Registration. NCT04796896.