Evaluation of Cellular Immune Responses After mRNA-1273 Vaccination in Children 6 Months to 11 Years of Age.

Abstract

Background: Cell-mediated immunity (CMI) may help protect against emerging 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-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 (51:17, 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.Trial registration number and URL NCT04796896 (https://clinicaltrials.gov/study/NCT04796896).