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Lessons From the First Pediatric mRNA-based Vaccine Study After COVID-19

May 13, 2024

Editor’s Note: Dr. Elif Ozdogan (she/her) is a second-year resident physician in Pediatrics at The Boston Combined Residency Program at Boston Children's Hospital and Boston Medical Center. She is interested in quality improvement and computational research and hopes to pursue further training in Transplant Medicine. -Rachel Y. Moon, MD, Associate Editor, Digital Media, Pediatrics

Vaccine research, in the wake of progress in adjuvant and mRNA technology, is rapidly advancing. As a result, clinical practice as the result of new pediatric vaccines may very well look different in the near future.

In an article being early released in Pediatrics this week entitled, “Safety and Immunogenicity of a Human Metapneumovirus and Parainfluenza Virus Type 3 Vaccine in Seropositive Children: Phase 1B Study,” Sabine Schnyder Ghamloush, MD, and colleagues at Moderna and MeridiTable San Clinical Research share the promising results of their early phase clinical trial on a combination mRNA-based vaccine, mRNA-1653, which encodes pre-fusion proteins of both Human Metapneumovirus (hMPV) and Parainfluenza Virus Type 3 (PIV3) (10.1542/peds.2023-064748). 

Early phase clinical trials such as this one assess the immunogenicity and safety of a vaccine on a small number of participants. The trial, conducted across multiple centers in the United States, used a randomized, observer-blind, placebo-controlled design.

Participants aged 18–55 months received two doses of mRNA-1653, with varying dosage levels, and were closely monitored for adverse reactions and immune responses. Children who were previously infected with and had antibodies against hMPV and PIV3 were included for safety considerations as is typical for vaccine trials in young children.

Immune response was assessed by changes in the neutralizing and binding antibody. In line with the preceding adult study of the same vaccine, the results were encouraging:

  • A single dose of mRNA-1653 increased neutralizing and binding antibody titers against hMPV-A, hMPV-B, and PIV3. Neutralization response against hMPV was more robust than response against PIV3.
  • Both 10 ug and 30 ug dose levels were effective in boosting antibody levels. The second injection at month 2 had little impact on humoral response.
  • Most common adverse reactions were local tenderness, irritability, chills, and sleepiness lasting 1–2 days. These reactions were similar to what was found in the prior COVID-19 vaccine research in children.
  • One participant experienced febrile seizure within 28 days of injection.

In the solicited commentary entitled “The Promise of New Vaccines Against Respiratory Viruses,” Robert L. Atmar, MD, and Hana M. El Sahly, MD, from Baylor College of Medicine pose the question of whether we should be surprised by these results (10.1542/peds.2023-065328). Their answer is no.

The past decade witnessed tremendous progress in the field of vaccine research. The mRNA technology that brought the 2023 Nobel Prize in Physiology or Medicine to Drs. Katalin Kariko and Drew Weissman is perhaps the most prominent but not the only technology to result in new vaccines.

A future in which we've modernized and expanded immunization schedules is within reach. Achieving this demands that we clinicians remain informed and figure out the optimal means of providing these vaccines to all our patients. For those interested, the article and the accompanied commentary are a great start.

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