A Phase 2 interventional study of mRNA-1647 and Placebo in Cytomegalovirus Infection, sponsored by ModernaTX, Inc.. Active, not recruiting at 3 sites in United States. Open to participants aged 18 Years and older. Per ClinicalTrials.gov, last updated 2026-08-10.
Sponsored by ModernaTX, Inc. (part of Moderna, Inc.) · Phase 2, Interventional, and Prevention
The main purpose of the study is to evaluate the efficacy and safety of mRNA-1647 compared to placebo to prevent first clinically significant cytomegalovirus infection (CS-CMVi) in the period following cessation of CMV prophylactic treatment (for example, letermovir) on Day 100 post-HCT through Month 9 post-HCT.
370 studies on the registry are indexed under Cytomegalovirus Infections; 57 are open to participants now.
This study's enrollment of 84 is above the median of 64 across 240 interventional studies indexed under Cytomegalovirus Infections.
Browse Cytomegalovirus Infections studies →ModernaTX, Inc. is the lead sponsor of 119 studies on the registry; 18 are open to participants now.
Of its 64 completed or terminated interventional studies of FDA-regulated products, 35 (55%) have results posted.
Counted across the registry records on this site, refreshed daily.
Go through the criteria one by one — yes, no or not sure — and take the list to your doctor or the study team. Kept in this browser only.
Exclusion Criteria:
Underlined terms in the criteria open these too. Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Stem cell (bone marrow) transplants. Allogeneic uses cells from a donor; autologous uses your own cells, collected earlier and given back.
After a transplant from a donor, the donor’s immune cells attack the recipient’s body, often the skin, gut or liver.
Able to become pregnant: from the first period until menopause, unless permanently unable to through surgery (removal of the womb, or of both ovaries or both fallopian tubes).
Criteria for people of childbearing potential usually ask for a negative pregnancy test and for contraception during the study and for a time after it.
Ways of preventing pregnancy. “Highly effective” methods fail less than 1% of the time a year when used correctly — for example an IUD or an implant.
Criteria usually say which methods count and how long to keep using them after the last dose, sometimes for male participants too. Some studies accept a partner’s vasectomy if it was confirmed successful and that person is the participant’s only sexual partner.
Before you join, the study team explains what taking part involves — its purpose, what happens, the risks and possible benefits — and answers your questions, so you can decide freely. Consent is usually recorded on a form (the informed consent form, ICF) signed by you or, where the law allows, by someone legally authorised to decide for you.
You can keep asking questions during the study, you are told of new information that matters, and you can choose to leave at any time.
The human immunodeficiency virus, which weakens the immune system.
Many studies now accept people whose HIV is controlled on treatment, judged by the viral load and the CD4 count. Check the limits this study sets.
A drug or device being studied in a clinical trial.
It may be new, or already approved and being studied for another use, dose or form. Criteria often leave out people who took part in another study of one within a recent period, commonly 30 days or five half-lives.
The other ingredients in a medicine besides the active drug, such as fillers, colours or preservatives.
Allogeneic and autologous transplant
Stem cell (bone marrow) transplants. Allogeneic uses cells from a donor; autologous uses your own cells, collected earlier and given back.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
GVHD (graft-versus-host disease)
After a transplant from a donor, the donor’s immune cells attack the recipient’s body, often the skin, gut or liver.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Childbearing potential
Able to become pregnant: from the first period until menopause, unless permanently unable to through surgery (removal of the womb, or of both ovaries or both fallopian tubes).
Criteria for people of childbearing potential usually ask for a negative pregnancy test and for contraception during the study and for a time after it.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Contraception
Ways of preventing pregnancy. “Highly effective” methods fail less than 1% of the time a year when used correctly — for example an IUD or an implant.
Criteria usually say which methods count and how long to keep using them after the last dose, sometimes for male participants too. Some studies accept a partner’s vasectomy if it was confirmed successful and that person is the participant’s only sexual partner.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Informed consent
Before you join, the study team explains what taking part involves — its purpose, what happens, the risks and possible benefits — and answers your questions, so you can decide freely. Consent is usually recorded on a form (the informed consent form, ICF) signed by you or, where the law allows, by someone legally authorised to decide for you.
You can keep asking questions during the study, you are told of new information that matters, and you can choose to leave at any time.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
HIV
The human immunodeficiency virus, which weakens the immune system.
Many studies now accept people whose HIV is controlled on treatment, judged by the viral load and the CD4 count. Check the limits this study sets.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Investigational drug or device
A drug or device being studied in a clinical trial.
It may be new, or already approved and being studied for another use, dose or form. Criteria often leave out people who took part in another study of one within a recent period, commonly 30 days or five half-lives.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Excipients
The other ingredients in a medicine besides the active drug, such as fillers, colours or preservatives.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Participants will receive mRNA-1647 by intramuscular (IM) injection on Day 42, Day 67, and Day 92, and a booster dose on Day 180.
Biological: mRNA-1647
Participants will receive mRNA-1647 matching placebo by IM injection on Day 42, Day 67, and Day 92, and a booster dose on Day 180.
Biological: Placebo
Lyophilized product that is reconstituted with 0.9% sodium chloride (normal saline).
0.9% sodium chloride (normal saline) injection
Time to the First Occurrence of an CS-CMVi Event as Measured by initiation of anti-CMV Antiviral Therapy
Time frame: Day 100 to Month 9
Number of Participants with Solicited Local and Systemic Reactogenicity Adverse Reactions (ARs)
Time frame: Up to Day 187 (7 days after last study injection)
Number of Unsolicited Adverse Events (AEs)
Time frame: Up to Day 205 (25 days after last study injection)
Number of Participants with Severe AEs
Time frame: Up to Day 365
Number of Participants with Serious Adverse Events (SAEs)
Time frame: Up to Day 365
Number of Participants with Grade ≥3 Acute Graft-Versus-Host Disease (GVHD)
Time frame: Up to Day 365
Number of Participants with First Occurrence of All CS-CMVi Events as Measured by Initiation of Anti-CMV Antiviral and/or End-Organ Disease
Time frame: Day 100 to Month 9
Number of Participants with an Occurrence of CMV Viremia
CMV Viremia is defined as ≥300 international units/milliliters (IU/mL).
Time frame: Day 100 to Month 9
Number of Participants with CMV End-Organ Disease
Time frame: Day 100 to Month 9
Duration of CMV Viremia
Time frame: Day 100 to Month 9
Duration of CMV Treatment
Time frame: Day 100 to Month 9
Number of Participants with Non-Relapse Mortality at 9 Months Post-HCT.
Time frame: Month 9
Titer of CMV-Specific Neutralizing Antibody (nAb)
Time frame: Days 42, 67, 92, 117, 180, 205 and 270
Geometric Mean Titer (GMT) of Anti-gB-Specific Immunoglobulin G (IgG) and Anti-Pentamer-Specific IgG as Measured by Enzyme-Linked Immunosorbent Assay (ELISA)
Time frame: Days 42, 67, 92, 117, 180, 205 and 270
Geometric Mean Concentration (GMC) of Anti-gB-Specific Immunoglobulin G (IgG) and Anti-Pentamer-Specific IgG as Measured by Enzyme-Linked Immunosorbent Assay (ELISA)
Time frame: Days 42, 67, 92, 117, 180, 205 and 270
Geometric Mean Fold Rise (GMFR) of Postbaseline/Baseline GMTs or GMCs
Time frame: Days 42, 67, 92, 117, 180, 205 and 270
Started Apr 2023 (actual). Primary completion is estimated for Mar 2027, 47 months after the start.
Of 29 phase 2 interventional studies under Cytomegalovirus Infections, half reached primary completion within 44 months of starting (the median), counting those still running; a quarter within 35 and three quarters within 62. This study's planned 47 months is close to that.
How these figures are worked out, and which studies are left out of them.
This study is active, not recruiting, as verified in Aug 2026. You cannot join it, but the record below documents what was studied.
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Studies of the drug tested here: mRNA-1647 cytomegalovirus vaccine