On December 12, 2024, the FDA in a briefing document “put on hold” all clinical trials of vaccines for respiratory syncytial virus (RSV) in infants. The FDA said it was notified by Moderna, in July 2024 that their findings from a clinical trial signaled safety concerns in infants. The two vaccine candidates were being evaluated during Phase 1 trial which primarily evaluates the drug’s, or vaccine’s safety and dose range.