Moderna has paused its mRNA RSV (Respiratory Syncytial Virus) vaccine trial for children after five infants were hospitalized with severe respiratory complications. This decision follows similar safety concerns recently acknowledged by the FDA, which halted enrollment in related trials for children under two years old.
The development came to light during Thursday’s FDA Vaccines and Related Biological Products Advisory Committee (VRBPAC) meeting. According to Fierce Pharma, panelists grappled with the safety implications of Moderna’s findings. Henry Bernstein, a professor of pediatrics at Hofstra/Northwell, noted, “This all seems like an incredible conundrum with lots of unanswered questions remaining—lots to still learn.”
The paused trial, labeled mRNA-1365-P101, was designed to evaluate the safety, tolerability, and immunogenicity of two mRNA-based vaccines, mRNA-1345 and mRNA-1365. These vaccines were intended to protect infants and toddlers against RSV.
The FDA briefing document explained, “A potential safety signal for RSV sLRTI (severe lower respiratory tract infection) was identified, and as additional information accrued, an imbalance in cases of RSV sLRTI was noted, with more cases identified in the vaccine groups compared with the control group. This raised a concern for possible VAERD (vaccine-associated enhanced respiratory disease).”
In the younger cohort phase of the study (5 months to <8 months), trial data revealed a concerning trend:
- Five cases of severe RSV-associated LRTI occurred among vaccinated infants who received lower doses of the vaccines.
- Only one case was reported in the placebo group.
- 26.3% of vaccinated infants with symptomatic RSV infections progressed to severe illness, compared to just 8.3% in the placebo group.
The trial’s pause was triggered by a pre-specified safety criterion: any severe LRTI with RSV-positive PCR in at least two participants. Upon reaching this threshold, Moderna halted enrollment and dosing in all study cohorts and notified the FDA and other regulators.
The FDA subsequently placed the trial on clinical hold, citing an “unreasonable and significant risk of illness or injury.” The pause affects studies involving infants aged 5 months to <24 months across multiple international sites.
While Moderna and the FDA emphasize that this decision reflects caution, some argue it highlights deeper issues with the “vaccine-first” approach. Public skepticism toward mRNA vaccines continues to grow, driven by safety concerns that remain unresolved.
Dr. Arnold Monto of the University of Michigan stressed the need for rigorous scrutiny, stating that RSV vaccines must be evaluated “on a platform-by-platform basis.” His comments underscore a larger concern: mRNA vaccines may pose unique risks that require further investigation.
