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mRNA-1647

Phase 2

Cytomegalovirus Infection | Monoclonal antibody | Infectious Disease |Moderna, Inc.|Last Updated: Aug 10, 2026

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Trial Design

RandomizedDouble-BlindPLACEBO_CONTROLLEDDMC
Total Trials5
Total Enrollment724

FDA Designations

No designations recorded

Clinical trial landscape

mRNA-1647 · 6 trials · 2 indications

Phase 2 3Phase 1 3
NCT05683457A Study to Evaluate the Efficacy, Safety, and Immunogenicity of mRNA-1647 Cytomegalovirus (CMV) Vaccine in Allogenic Hematopoietic Cell Transplantation (HCT) Participants.Cytomegalovirus Infection
ACTIVE NOT_RECRUITING84 Analytics
NCT04975893A Long-Term Extension Study to Evaluate the Immunogenicity and Safety of Cytomegalovirus (CMV) mRNA-1647 VaccineCytomegalovirus Infection
COMPLETED135 Analytics
NCT04232280Dose-Finding Trial to Evaluate the Safety and Immunogenicity of Cytomegalovirus (CMV) Vaccine mRNA-1647 in Healthy AdultsCytomegalovirus Infection
COMPLETED315 Analytics
PHASE2ACTIVE NOT_RECRUITING
A Study to Evaluate the Efficacy, Safety, and Immunogenicity of mRNA-1647 Cytomegalovirus (CMV) Vaccine in Allogenic Hematopoietic Cell Transplantation (HCT) Participants.
Cytomegalovirus InfectionUnlock trial analytics
PHASE2COMPLETED
A Long-Term Extension Study to Evaluate the Immunogenicity and Safety of Cytomegalovirus (CMV) mRNA-1647 Vaccine
Cytomegalovirus InfectionUnlock trial analytics
PHASE2COMPLETED
Dose-Finding Trial to Evaluate the Safety and Immunogenicity of Cytomegalovirus (CMV) Vaccine mRNA-1647 in Healthy Adults
Cytomegalovirus InfectionUnlock trial analytics

Study Endpoints

Primary Endpoints

Time to the First Occurrence of an CS-CMVi Event as Measured by initiation of anti-CMV Antiviral Therapy
Day 100 to Month 9
Number of Participants with Solicited Local and Systemic Reactogenicity Adverse Reactions (ARs)
Up to Day 187 (7 days after last study injection)
Number of Unsolicited Adverse Events (AEs)
Up to Day 205 (25 days after last study injection)
Number of Participants with Severe AEs
Up to Day 365
Number of Participants with Serious Adverse Events (SAEs)
Up to Day 365
Number of Participants with Grade ≥3 Acute Graft-Versus-Host Disease (GVHD)
Up to Day 365
Primary Extension Phase: Geometric Mean Titers (GMTs) of Antigen-Specific Neutralizing Antibody (nAb) and Binding Antibody (bAb)
Up to 3 years
BP: GMTs of Antigen-Specific nAb and bAb
BP Month 0, BP Month 1, BP Month 3, BP Month 6, and BP Month 12
BP: Number of Participants with Solicited Adverse Reactions (ARs)
Up to BP Day 7 (7 days after BP vaccination)
BP: Number of Participants with Unsolicited Adverse Events (AEs)
Up to BP Day 28 (28 days after BP vaccination)
BP: Number of Participants with Medically-Attended AEs (MAAEs)
Up to BP Month 6 (6 months after BP vaccination)
BP: Number of Participants with Adverse Events of Special Interest (AESIs), Serious Adverse Events (SAEs), and AEs Leading to Discontinuation of Study
Up to BP Month 12
Number of Participants With Solicited Local and Systemic Adverse Reactions (ARs)
Up to Day 175 (7 days following last dose administration)

Solicited ARs were selected signs and symptoms occurring after vaccination administration during a specified post-vaccination follow-up period. The occurrence and intensity of the selected signs and symptoms was actively solicited from the participant during a specified post-vaccination follow-up period (day of vaccination and 6 subsequent days), using a predefined checklist in the electronic diary. The following local ARs were solicited: pain at injection site, erythema (redness) at injection site, swelling/induration (hardness) at injection site, and localized axillary swelling or tenderness ipsilateral to the vaccination arm. The following systemic ARs were solicited: headache, fatigue, myalgia (muscle aches all over the body), arthralgia (aching in several joints), nausea/vomiting, rash, fever, and chills. A summary of all Serious Adverse Events and Other Adverse Events (nonserious) regardless of causality is located in the 'Reported Adverse Events' Section.

Number of Participants With Unsolicited Adverse Events (AEs)
Up to Day 196 (28 days following last dose administration)

An unsolicited AE was defined as any untoward medical occurrence associated with the use of a drug in humans, whether or not considered drug related. The treatment-emergent AEs are defined as any event not present before exposure to study drug or any event already present that worsened in intensity or frequency after exposure. A summary of all Serious Adverse Events and Other Adverse Events (nonserious) regardless of causality is located in the 'Reported Adverse Events' Section."

Number of Participants With Medically Attended Adverse Events (MAAEs)
Up to Day 336 (6 months following last dose administration)

An MAAE is an AE that lead to a visit to a healthcare practitioner (HCP). This would include visits to study clinic for unscheduled assessments (for example, rash assessment, abnormal laboratory follow-up), and visits to HCPs external to the clinical site (for example, urgent care, primary care physician). A summary of all Serious Adverse Events and Other Adverse Events (nonserious) regardless of causality is located in the 'Reported Adverse Events' Section."

Geometric Mean Titer (GMT) of Serum Neutralizing Anti-CMV Antibodies Against Epithelial Cell Infection and Against Fibroblast Infection
Baseline (Day 1), Day 29, Day 56, Day 84, Day 168, Day 196, Day 336, Day 504

Blood samples for antibody-mediated immunogenicity (AMI) analysis were collected during protocol-specified study visits. Serological assessment of serum anti-CMV neutralizing antibody titers against epithelial cell infection and fibroblast infection were measured by a neutralization assay. Results are reported as fold dilution (titer). GMT 95% confidence interval (CI) was calculated based on the t-distribution of the log-transformed values then back transformed to the original scale for presentation.

Geometric Mean Ratio (GMR) of Serum Neutralizing Anti-CMV Antibodies Against Epithelial Cell Infection and Against Fibroblast Infection
Day 29, Day 56, Day 84, Day 168, Day 196, Day 336, Day 504

Blood samples for antibody-mediated immunogenicity analysis were collected during protocol-specified study visits. Serological assessment of serum anti-CMV neutralizing antibody titers against epithelial cell infection and fibroblast infection were measured by a neutralization assay. The GMR measures the changes in immunogenicity titers within participants. Results are reported as a ratio (post-baseline/baseline titers). GMR 95% CI was calculated based on the t-distribution of the log-transformed values then back transformed to the original scale for presentation.

Percentage of Participants With ≥2-Fold, 3-Fold, and 4-Fold Increases in Neutralizing Antibodies (nAb) Over Baseline Against Epithelial Cell Infection and Against Fibroblast Infection
Day 29, Day 56, Day 84, Day 168, Day 196, Day 336, Day 504

Blood samples for antibody-mediated immunogenicity analysis were collected during protocol-specified study visits. Serological assessment of serum anti-CMV nAb titers against epithelial cell infection and fibroblast infection were measured by a neutralization assay. A ≥z-fold increase from baseline at participant level was defined as a ≥z \* the lower limit of quantification (LLOQ) for participants with baseline antibody level below the LLOQ, or a z-times or higher-level ratio in participants with baseline antibody level equal to or above the LLOQ. LLOQ=16. Results are reported as percentage of participants with ≥2-fold, 3-fold, and 4-fold increases in serum anti-CMV nAb titers from baseline. 95% CI for percentage is calculated using the Clopper-Pearson method.

Number of Solicited Local and Systemic Reactogenicity Adverse Reactions (ARs)
Up to Day 176 (7 days after each study injection)
Number of Medically Attended Adverse Events (MAAEs)
Up to Day 347 (6 months after the last study injection)
Number of Serious Adverse Events (SAEs), Adverse Events of Special Interest (AESIs), and AEs Leading to Discontinuation
Up to Day 527 (end of study)
Geometric Mean Titer (GMT) of Anti-CMV Neutralizing Antibodies (nAbs)
Up to Day 527 (end of study)

Serum functional antibody levels against vaccine antigens will be measured by nAb titer against epithelial cell infection and nAb titer against fibroblast infection.

Geometric Mean Fold-Rise (GMFR) of Anti-CMV nAbs
Up to Day 527 (end of study)

Serum functional antibody levels against vaccine antigens will be measured by nAb titer against epithelial cell infection and nAb titer against fibroblast infection.

Number of Participants with ≥2-Fold, 3-Fold, and 4-Fold increases Over Baseline of Anti-CMV Antibodies
Up to Day 527 (end of study)

Serum functional antibody levels against vaccine antigens will be measured by nAb titer against epithelial cell infection and nAb titer against fibroblast infection.

Number of Participants With Medically-Attended AEs (MAAEs)
Day 1 through 6 months after the last injection (up to Day 347)
Number of Participants With Serious AEs (SAEs)
Day 1 through End of Study (EOS) (up to Day 347)
Number of Participants With AEs of Special Interest (AESIs)
Day 1 through EOS (up to Day 347)
Frequency of solicited AEs (local and systemic reactogenicity events)
7 days following each dose administration
Frequency of unsolicited adverse events
29 days following each dose administration
Frequency of medically-attended AEs, adverse events of special interest (AESI), and serious adverse events (SAE)
one year following the last dose administration
Frequency of clinical laboratory adverse events
1 month following the last dose administration

Secondary Endpoints

Number of Participants with First Occurrence of All CS-CMVi Events as Measured by Initiation of Anti-CMV Antiviral and/or End-Organ Disease
Day 100 to Month 9
Number of Participants with an Occurrence of CMV Viremia
Day 100 to Month 9
Number of Participants with CMV End-Organ Disease
Day 100 to Month 9
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Study Design & Arms

AllocationRANDOMIZED
MaskingTRIPLE
ModelPARALLEL
PurposePREVENTION

Treatment Arms

ArmTypeDescription
mRNA-1647EXPERIMENTALParticipants will receive mRNA-1647 by intramuscular (IM) injection on Day 42, Day 67, and Day 92, and a booster dose on Day 180.
PlaceboPLACEBO_COMPARATORParticipants will receive mRNA-1647 matching placebo by IM injection on Day 42, Day 67, and Day 92, and a booster dose on Day 180.
Primary Extension PhaseOTHERCMV-seropositive and CMV-seronegative participants who completed Study mRNA-1647-P202 will be followed every 6 months for 3 years in this study after the final visit in Study mRNA-1647-P202.
Optional Booster Phase - BD RecipientsEXPERIMENTALParticipants who opted to enroll into the optional Booster Phase will receive a single mRNA-1647 vaccine dose.
Optional Booster Phase - Observational GroupOTHERParticipants who opted to enroll into the Observational Group will be followed in the optional BP until BP Month 12.
mRNA-1647 Dose Level AEXPERIMENTALParticipants will receive mRNA-1647 vaccine at Dose Level A by intramuscular (IM) injection on Day 1, Day 56, and Day 168.
mRNA-1647 Dose Level BEXPERIMENTALParticipants will receive mRNA-1647 vaccine at Dose Level B by IM injection on Day 1, Day 56, and Day 168.
mRNA-1647 Dose Level CEXPERIMENTALParticipants will receive mRNA-1647 vaccine at Dose Level C by IM injection on Day 1, Day 56, and Day 168.
mRNA-1647 Dose AEXPERIMENTALCMV-seronegative or CMV-seropositive participants 9 to 15 years of age will receive mRNA-1647 at Dose Level A by intramuscular (IM) injection given as a 3-injection series on Day 1, Month 2, and Month 6.
mRNA-1647 Dose BEXPERIMENTALCMV-seronegative or CMV-seropositive participants 9 to 15 years of age will receive mRNA-1647 at Dose Level B by IM injection given as a 3-injection series on Day 1, Month 2, and Month 6.
mRNA-1647 Dose CEXPERIMENTALCMV-seronegative or CMV-seropositive participants 9 to 15 years of age and 16 to 25 years of age will receive mRNA-1647 at Dose Level C by IM injection given as a 3-injection series on Day 1, Month 2, and Month 6.
Dose Expansion: mRNA-1647 (3-dose Schedule)EXPERIMENTALCMV-seronegative or CMV-seropositive participants 9 to 15 years of age will receive mRNA-1647 at selected dose level by IM injection given as a 3-injection series on Day 1, Month 2, and Month 6.
Dose Expansion: mRNA-1647 (2-dose Schedule)EXPERIMENTALCMV-seronegative participants 9 to 15 years of age will receive mRNA-1647 at selected dose level by IM injection given as a 2-injection series on Day 1 and Month 6.
Dose Expansion: Placebo (3-dose Schedule)PLACEBO_COMPARATORCMV-seronegative or CMV-seropositive participants 9 to 15 years of age will receive placebo by IM injection given as a 3-injection series on Day 1, Month 2, and Month 6.
Dose Expansion: Placebo (2-dose Schedule)PLACEBO_COMPARATORCMV-seronegative participants 9 to 15 years of age will receive placebo by IM injection given as a 2-injection series on Day 1 and Month 6.
mRNA-1443EXPERIMENTAL -

Interventions

NameTypeDescription
mRNA-1647BIOLOGICALLyophilized product that is reconstituted with 0.9% sodium chloride (normal saline).
PlaceboBIOLOGICAL0.9% sodium chloride (normal saline) injection
mRNA-1443BIOLOGICALEscalating dose levels
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Eligibility Criteria

Age Range18 Years to N/A
SexALL
Healthy VolunteersNo
Study Sites3

Inclusion Criteria: * Receipt of an allogeneic HCT. * CMV-seropositive, defined as a documented positive test for anti-CMV IgG. * High-risk for CMV: HCT from related, unrelated, or haploidentical donor with post-transplant cyclophosphamide for graft-versus-host-disease (GVHD) prophylaxis; or HCT fr...

Countries:United StatesCanadaUnited Kingdom
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Recent Changes (Last 90 Days)

MEDIUMAug 11, 2026NCT05683457primaryCompletionDate: changed
MEDIUMAug 11, 2026NCT05683457primaryCompletionDate: changed
MEDIUMAug 11, 2026NCT05683457primaryCompletionDate: changed
MEDIUMJul 5, 2026NCT05575492TRIAL_REMOVED: changed
MEDIUMJul 5, 2026NCT05575492TRIAL_REMOVED: changed
MEDIUMJul 5, 2026NCT05575492TRIAL_REMOVED: changed

Frequently asked questions about mRNA-1647

What is mRNA-1647 used for?

mRNA-1647 is an investigational vaccine being developed for the prevention of Cytomegalovirus (CMV) infection. It is currently in Phase 1 clinical development, with studies also conducted in Phase 2. The vaccine is designed to elicit an immune response against CMV, a common virus that can cause serious complications in immunocompromised individuals and during pregnancy.

Who makes mRNA-1647?

mRNA-1647 is being developed by Moderna, Inc., a biotechnology company traded on the NASDAQ under the ticker symbol MRNA. Moderna is conducting clinical trials to evaluate the safety, reactogenicity, and immunogenicity of this investigational CMV vaccine in various populations.

What phase is mRNA-1647 in?

mRNA-1647 is currently in Phase 1 clinical development. While some completed trials were designated as Phase 1 and Phase 2, the overall development stage is Phase 1. It is an investigational vaccine and has not been approved by regulatory authorities. Clinical trials are ongoing to assess its efficacy, safety, and immunogenicity.

What clinical trials is mRNA-1647 in?

mRNA-1647 has been studied in several clinical trials, including NCT03382405, a Phase 1 study in healthy adults; NCT04975893, a long-term extension study; NCT05105048, a Phase 1 study; and NCT05683457, a Phase 2 study in allogeneic hematopoietic cell transplantation participants. These trials have evaluated the vaccine's safety, reactogenicity, and immunogenicity.

Is mRNA-1647 FDA approved?

No, mRNA-1647 is not FDA approved. It is an investigational vaccine currently in Phase 1 clinical development. Clinical trials are being conducted to evaluate its safety and efficacy, but it has not yet received regulatory approval for use in the prevention of Cytomegalovirus infection.

How does mRNA-1647 work?

mRNA-1647 is an mRNA-based vaccine that works by encoding antigens from Cytomegalovirus (CMV). When administered, it instructs cells to produce these viral proteins, triggering an immune response. This response is intended to protect against CMV infection. The vaccine is being studied for its ability to generate neutralizing antibodies and cellular immunity.