FDA Halts Moderna's Norovirus Vaccine Trial Over Guillain-Barré Case

Moderna's phase 3 trial for its norovirus vaccine candidate, mRNA-1403, has been placed on hold by the U.S. Food and Drug Administration (FDA) following a reported case of Guillain-Barré syndrome, the company announced in its fourth-quarter earnings release on February 14, 2025.

Trial Details and Enrollment Status

The large-scale study, which aims to evaluate the vaccine's efficacy against moderate to severe norovirus acute gastroenteritis in adults, has already completed enrollment in the Northern Hemisphere. Moderna began dosing patients in September 2024 and is preparing for enrollment in the Southern Hemisphere.

The trial's target is to recruit approximately 25,000 participants, including 20,000 adults aged 60 years and older and 5,000 between 18 and 59 years old. Moderna emphasized that the study focuses particularly on the older age group, which faces the highest risk of severe outcomes, including hospitalization.

Guillain-Barré Syndrome and Vaccine Safety

Guillain-Barré syndrome, a rare autoimmune disorder causing the immune system to attack the nerves, has been previously associated with other vaccine trials. Notably, similar concerns have arisen in trials for respiratory syncytial virus (RSV) vaccines, including Pfizer's Abrysvo and GSK's Arexvy.

Moderna stated that the single case of Guillain-Barré syndrome in the mRNA-1403 trial is currently under investigation. Despite the hold, the company does not anticipate an impact on the study's efficacy readout timeline, as enrollment in the Northern Hemisphere has already been completed.

mRNA-1403: Moderna's Norovirus Vaccine Candidate

Moderna's mRNA-1403 is designed as a trivalent formulation containing mRNA encoded for virus-like particles. The vaccine aims to protect against multiple norovirus genotypes, addressing a significant unmet medical need in infectious disease prevention.

While the FDA hold presents a setback, Moderna maintains that the timing of the phase 3 readout will depend on case accruals. The pharmaceutical industry and health authorities will closely monitor the investigation's outcomes, as they may have broader implications for mRNA vaccine development and safety protocols in clinical trials.