CMV Vaccine Fails to Meet Efficacy Goals
Moderna has decided to discontinue development of its mRNA-based vaccine for congenital cytomegalovirus (CMV) after the candidate couldn’t meet efficacy goals in a large phase 3 study, the company disclosed in an announcement.
Although mRNA-1647 demonstrated an acceptable tolerability profile, its effectiveness in preventing CMV infection fell short of expectations, with protection rates ranging from just 6% to 23%, depending on how infection was defined.
Details of the Phase 3 Study
The phase 3 study included 7,454 women aged 16 to 40 across 13 countries. Congenital CMV occurs when a newborn contracts the virus from the mother during childbirth. While CMV often remains dormant in most infected individuals, it can reactivate over time, and in infants, may lead to growth delays, hearing impairment, and other serious issues.
According to estimates from the Centers for Disease Control and Prevention, over half of all adults contract CMV by the time they reach 40 years of age.
In the announcement, Moderna President Stephen Hoge expressed disappointment that the vaccine did not prevent initial infection, noting that after decades of research, there is still no vaccine capable of stopping congenital CMV.
In a separate blog post, CEO Stéphane Bancel described the trial as especially difficult because its goal was to block new infections caused by a dormant virus rather than to prevent visible illness. She noted that this study stands out within their research portfolio, as it was the sole clinical trial designed with the prevention of initial infection as its main goal.
Future Research and Financial Outlook
Moderna will continue investigating whether the vaccine can prevent CMV reactivation following bone marrow transplantation, Hoge said in the announcement. The ongoing phase 2 study aims to enroll over 220 participants and is expected to conclude by August next year.
The company added that halting development of the vaccine will not affect its 2025 financial outlook or its goal to achieve breakeven in 2028.
Shift in Focus to Oncology
The discontinuation of the congenital CMV vaccine program, coupled with mounting federal scrutiny of mRNA vaccines, has intensified pressure on Moderna’s oncology division to produce meaningful results. Speaking at the 2025 European Society for Medical Oncology (ESMO) conference, Moderna’s head of oncology, Kyle Holen noted that most of the company’s forthcoming investigational new drug (IND) filings will focus on cancer indications rather than infectious diseases.
At the same event, Moderna unveiled phase 1/2 results from a 29-patient study (with each getting two doses) testing its experimental cancer vaccine mRNA-4359 alongside Merck & Co.’s Keytruda. The combination achieved an objective response rate of 24% among evaluable patients. Encouraged by these findings, Holen confirmed that Moderna plans to expand development of mRNA-4359 into lung cancer.
CMV remains a leading cause of congenital infection worldwide, with significant outcomes including hearing loss, developmental disabilities and other serious health impacts.
With Moderna’s withdrawal of the congenital CMV programme, other developers and public health bodies may increase focus on alternate vaccine approaches for CMV, such as subunit, viral vector, and other novel platforms.
For Moderna, the setback underscores the risks inherent in vaccine development — particularly for pathogens with challenging biology — and may lead to tactical shifts in how mRNA vaccine candidates are prioritised and advanced.
In conclusion, Moderna’s decision to halt the congenital CMV vaccine programme represents a significant pivot for the company. While the technology and ambition remain, the path forward will require recalibration. The broader scientific community will now look to integrate the insights from this trial into next-generation CMV vaccine candidates.
Looking ahead, Moderna’s experience with the CMV vaccine serves as a reminder of both the potential and the limitations of mRNA science. The lessons learned from this programme will likely influence future vaccine design strategies and clinical trial methodologies across the biotech industry.
