Moderna, Inc. (MRNA) saw its stock price plummet 5.40% in after-hours trading following a significant setback in its vaccine development program. The biotech company announced that its experimental cytomegalovirus (CMV) vaccine failed to meet the primary efficacy endpoint in a crucial Phase 3 trial, leading to the discontinuation of its development for congenital CMV.

The vaccine, known as mRNA-1647, was designed to prevent CMV infection, a common cause of birth defects. However, the late-stage trial involving approximately 7,500 women aged 16 to 40 showed disappointing results. Vaccine efficacy against infection ranged from just 6% to 23%, falling well below Moderna's target. This outcome represents a significant blow to efforts in preventing congenital CMV, for which there is currently no approved vaccine.

Despite the setback, Moderna stated that it does not anticipate any impact on its 2025 financial guidance or its expectation of achieving breakeven in 2028. The company will continue to evaluate mRNA-1647 in an ongoing Phase 2 trial for bone marrow transplant patients. However, the failure of this high-profile vaccine candidate in a large market has clearly shaken investor confidence, as reflected in the sharp after-hours stock decline.