In short
MRNA encoding human cytomegalovirus glycoprotein H is an investigational messenger RNA (mRNA) vaccine component being studied to prevent cytomegalovirus (CMV) infection. It is part of a multi-component vaccine candidate known as mRNA-1647, developed by Moderna. A Phase 3 trial of mRNA-1647 enrolled 7,484 healthy participants aged 16 to 40 years and has been completed.
Key points
- Phase 3 trial completed in healthy participants aged 16 to 40 years
- 7,484 participants enrolled to evaluate efficacy, safety, and immunogenicity
- Studied for prevention of primary cytomegalovirus (CMV) infection in seronegative females
- Vaccine given as a 3-dose intramuscular injection schedule
- Primary outcome measured seroconversion to CMV antigens not encoded by the vaccine
- An mRNA-based vaccine candidate with a paediatric investigation plan under EMA review
What is mRNA encoding human cytomegalovirus glycoprotein H?
MRNA encoding human cytomegalovirus glycoprotein H is an investigational messenger RNA (mRNA) component of a vaccine candidate. It is part of a multi-antigen vaccine known as mRNA-1647, which also includes mRNA encoding other CMV proteins: glycoprotein B, glycoprotein L, UL128, UL130, and UL131A. The substance is not yet an authorised medicine; it remains under investigation. Moderna Biotech Spain S.L. is the company developing this vaccine candidate.
How does mRNA encoding human cytomegalovirus glycoprotein H work?
The vaccine uses messenger RNA to instruct cells in the body to produce the cytomegalovirus glycoprotein H protein. This protein is part of the pentameric complex that CMV uses to enter human cells. By presenting this viral protein to the immune system, the vaccine aims to train the body to recognise and fight CMV before an actual infection occurs. Glycoprotein H is one of several CMV proteins included in the mRNA-1647 vaccine, along with glycoprotein B, glycoprotein L, UL128, UL130, and UL131A.
Which conditions is it used or studied for?
- Cytomegalovirus infection (CMV) — a common viral infection that can cause serious health problems in unborn babies when a pregnant woman is infected for the first time during pregnancy, and in people with weakened immune systems.
How is mRNA encoding human cytomegalovirus glycoprotein H given?
In the clinical trial, the vaccine was administered as an intramuscular injection on a 3-dose schedule. The trial used a 100 microgram dose of mRNA-1647, given into the muscle.
What do the clinical trials show?
One completed Phase 3 trial (NCT05085366) evaluated mRNA-1647 in 7,484 healthy participants aged 16 to 40 years. The trial aimed to demonstrate the efficacy of the vaccine in preventing primary CMV infection in CMV-seronegative female participants, and to evaluate safety and reactogenicity on a 3-dose injection schedule in all participants.
The primary outcome measured seroconversion from a negative to a positive result for serum IgG against four recombinant CMV antigens not encoded by the vaccine (pp150, pp28, pp52, pp38), assessed starting 28 days after the third injection. Safety was assessed through solicited adverse reactions through 7 days after each injection, unsolicited adverse events through 28 days after each injection, medically attended adverse events from Day 1 through 6 months after the last injection, adverse events of special interest from Day 1 through end of study, and serious adverse events from time of consent through end of study.
Participants were healthy individuals aged 16 to 40 years. The trial is now completed. A paediatric investigation plan for this vaccine candidate has been accepted by the European Medicines Agency with a modification agreed on 29 January 2026.
What side effects are known?
The Phase 3 trial collected data on solicited adverse reactions through 7 days after each injection, unsolicited adverse events through 28 days, medically attended adverse events, adverse events of special interest, and serious adverse events. The supplementary sources provided do not report specific side effect frequencies or types for this vaccine candidate.