Safety and Immunogenicity of an mRNA-Based hMPV/PIV3 Combination Vaccine in Seropositive Children

Abstract

OBJECTIVES: Human metapneumovirus (hMPV) and parainfluenza virus type 3 (PIV3) are common respiratory illnesses in children. The safety and immunogenicity of an investigational mRNA-based vaccine, mRNA-1653, encoding membrane-anchored fusion proteins of hMPV and PIV3, was evaluated in hMPV/PIV3-seropositive children. METHODS: In this phase 1b randomized, observer-blind, placebo-controlled, dose-ranging study, hMPV/PIV3-seropositive children were enrolled sequentially into 2 dose levels of mRNA-1653 administered 2 months apart; children aged 12 to 36 months were randomized (1:1) to receive 10-mg of mRNA-1653 or placebo and children aged 12 to 59 months were randomized (3:1) to receive 30-mg of mRNA-1653 or placebo. RESULTS: Overall, 27 participants aged 18 to 55 months were randomized; 15 participants received 10-mg of mRNA-1653 (n 5 8) or placebo (n 5 7), whereas 12 participants received 30-mg of mRNA-1653 (n 5 9) or placebo (n 5 3). mRNA-1653 was well-tolerated at both dose levels. The only reported solicited local adverse reaction was tenderness at injection site; solicited systemic adverse reactions included grade 1 or 2 chills, irritability, loss of appetite, and sleepiness. A single 10-mg or 30-mg mRNA-1653 injection increased hMPV and PIV3 neutralizing antibody titers (geometric mean fold-rise ratio over baseline: hMPV-A 5 2.9–6.1; hMPV-B 5 6.2–13.2; PIV3 5 2.8–3.0) and preF and postF binding antibody concentrations (geometric mean fold-rise ratio: hMPV preF 5 5.3–6.1; postF 5 4.6–6.5 and PIV3 preF 5 13.9–14.2; postF 5 11.0–12.1); a second injection did not further increase antibody levels in these seropositive children. Binding antibody responses were generally preF biased. CONCLUSIONS: mRNA-1653 was well-tolerated and boosted hMPV and PIV3 antibody levels in seropositive children aged 12 to 59 months, supporting the continued development of mRNA-1653 or its components for the prevention of hMPV and PIV3.