Moderna ends development of congenital CMV vaccine after late-stage failure

US biotech Moderna (Nasdaq: MRNA) is discontinuing its once-promising vaccine for congenital cytomegalovirus (CMV) after the shot failed to prevent primary infection in healthy women during a Phase III study. The decision marks a setback for the company’s post-pandemic vaccine ambitions, sending its shares down about 5% in after-hours trading on Wednesday.

The pivotal trial enrolled around 7,500 women aged 16 to 40 across 13 countries, making it the largest CMV vaccine study to date. Moderna had aimed for around 50% efficacy for its candidate, mRNA-1647, but results fell well short, with protection ranging from 6% to 23%, depending on case definition. The vaccine was generally well-tolerated, and no safety concerns were raised by monitors.

Chief executive Stéphane Bancel described the outcome as “disappointing for families and healthcare professionals” awaiting a vaccine for congenital CMV, which remains the leading infectious cause of birth defects in the USA. President Stephen Hoge added that the company will continue testing mRNA-1647 in bone marrow transplant patients, where CMV reactivation can cause serious complications.