HQ Team
December 11, 2024: The U.S. Food and Drug Administration (FDA) has announced a halt to all clinical trials for respiratory syncytial virus (RSV) vaccines targeting young children and infants following data regarding the safety of Moderna’s vaccine candidates. This decision comes ahead of an advisory committee meeting scheduled for later this week, where experts will discuss the implications of these findings.
The FDA reported an “imbalance in severe/very severe cases” of RSV lower respiratory tract infections (LRTI) among infants participating in trials for Moderna’s mRNA-1345 and mRNA-1365 vaccines. In a cohort study involving 20 infants who received mRNA-1365, 10 developed symptomatic RSV, with three cases classified as severe. Comparatively, in the placebo group, 12 out of 20 infants contracted RSV, with only one experiencing a severe case.
Moderna previously discontinued mRNA-1345 in September due to similar safety concerns, which were first flagged on July 17 when two or more study participants exhibited severe LRTI following vaccination. The company informed the FDA of a study-wide pause just two days later.
Future of pediatric vaccine development
The FDA’s findings raise significant questions about the safety of non-live attenuated RSV vaccines for infants and toddlers. The agency cautioned that the current data may have “uncertain implications” for ongoing and future pediatric studies. In light of past experiences with vaccine-associated enhanced respiratory disease (VAERD) during the 1960s, where early RSV vaccine trials resulted in severe outcomes for some infants, experts are urged to consider potential risks carefully before proceeding with new trials.
Broader context of RSV vaccine development
Moderna’s setbacks occur against a backdrop of increasing interest in RSV vaccine development. In May 2023, the FDA approved Pfizer’s maternal immunization vaccine designed to protect infants during their first six months of life by transferring antibodies from mothers to babies.
This approval followed compelling Phase 3 efficacy and safety data presented by Pfizer during advisory committee meetings. Despite the current hold on pediatric trials, other companies continue to advance their RSV vaccine candidates. Pfizer’s bivalent vaccine has shown promising results in older adults, demonstrating an 80% effectiveness rate in preventing serious outcomes related to RSV.
Market reaction and future outlook
Following the FDA’s announcement, Moderna’s stock experienced a decline of approximately 5%. The company has not yet commented publicly on the recent developments.
As the advisory committee convenes this Thursday, they will discuss whether existing evidence indicates broader safety concerns applicable to other RSV vaccine candidates for young children. While the halt on RSV vaccine trials presents significant challenges for public health efforts aimed at protecting vulnerable populations from this common respiratory virus, it also underscores the importance of rigorous safety evaluations in vaccine development processes.
