Moderna has announced that its Phase 3 trial for the cytomegalovirus (CMV) vaccine candidate, mRNA-1647, did not meet its primary endpoint. As a result, the company is discontinuing its congenital CMV clinical development program.

“Today’s outcome is disappointing for families and healthcare professionals who have long awaited a vaccine to prevent congenital CMV, a leading infectious cause of birth defects,” said Stéphane Bancel, Chief Executive Officer of Moderna.

“While the trial did not achieve its goal, we remain committed to scientific transparency and will share the full data with the research community to help advance the global effort toward a CMV vaccine. We are deeply grateful to our clinical teams, partners, and participants who made this work possible.”

The Phase 3 study was a randomized, observer-blind, placebo-controlled trial enrolling approximately 7,500 women across 13 countries—the largest CMV vaccine efficacy trial conducted to date. Vaccine efficacy against primary CMV infection ranged from 6 per cent to 23 per cent, depending on case definition, falling short of Moderna’s predefined target.

“We are clearly disappointed by these results, as preventing primary CMV infection remains an urgent unmet need,” said Stephen Hoge, M.D., President of Moderna. “However, CMV continues to cause serious disease in other settings, including viral reactivation in bone marrow transplant patients. We will continue to explore the potential of mRNA-1647 in this high-risk population through our ongoing Phase 2 study.”

mRNA-1647 was generally well tolerated, regardless of CMV serostatus, with a safety profile consistent with earlier studies. No safety concerns were identified by the Data and Safety Monitoring Board. Moderna’s Phase 2 trial evaluating mRNA-1647 in bone marrow transplant patients will continue as planned.

The company does not anticipate any impact on its 2025 financial guidance or its expectation of achieving breakeven in 2028. Moderna had projected limited near-term revenue contribution from mRNA-1647 given the investment required for market development and launch, and had expected the program to be cash-flow negative through 2028.