A Long-Term Extension Study to Evaluate the Immunogenicity and Safety of Cytomegalovirus (CMV) mRNA-1647 Vaccine

January 30, 2026 updated by: ModernaTX, Inc.

A Phase 2, Non-Randomized, Long-Term Extension Study to Evaluate the Immunogenicity and Safety of Cytomegalovirus mRNA-1647 Vaccine Including a Booster Dose in a Subset of Participants Who Completed Study mRNA-1647-P202

The main purpose of the extension phase of this study is to evaluate the longer-term immune persistence of mRNA-1647 vaccine administered to CMV-seronegative and CMV-seropositive adults who completed Study mRNA-1647-P202 (NCT04232280). For participants in the optional booster phase (BP), the main purpose is to evaluate the long-term immunogenicity and safety of the mRNA-1647 vaccine in both participants receiving a booster dose (BD) and those not receiving a BD, and to additionally evaluate the reactogenicity in participants receiving a BD.

Study Overview

Status

Completed

Conditions

Intervention / Treatment

Detailed Description

The study aims to explore the long-term potential differences in immunogenicity and key safety parameters following mRNA-1647 administration, participants who completed study mRNA-1647-P202, who are CMV-seronegative and who did not seroconvert due to primary CMV infection during the study will be enrolled. Study mRNA-1647-P202 participants who were CMV-seropositive at baseline, randomized to receive mRNA-1647 injection, and completed their final study visit will also be enrolled.

No study treatment will be administered during the primary extension phase of this study. Eligible participants enrolling in the primary extension phase who completed Study mRNA-1647-P202 may have received mRNA-1647 (either low dose, medium dose, or high dose) or placebo in CMV-seronegative participants and mRNA-1647 (either low dose, medium dose, or high dose) in CMV-seropositive participants.

In the optional BP, consenting and eligible participants will receive a single BD of the mRNA-1647 vaccine (medium dose). In the Observational Group of the optional BP, consenting and eligible participants will not receive study treatment.

Study Type

Interventional

Enrollment (Actual)

135

Phase

  • Phase 2

Contacts and Locations

This section provides the contact details for those conducting the study, and information on where this study is being conducted.

Study Locations

  • United States
    • Illinois
      • Peoria, Illinois, United States, 61610
        • Optimal Research, LLC
    • Kansas
      • Lenexa, Kansas, United States, 66219
        • Johnson County Clin-Trials, Inc.
    • Kentucky
      • Lexington, Kentucky, United States, 40509
        • Alliance for Multispeciality Research, LLC
    • Texas
      • Austin, Texas, United States, 78745
        • Tekton Research Inc
      • Victoria, Texas, United States, 77901
        • Crossroads Clinical Research (Victoria)
    • Utah
      • Salt Lake City, Utah, United States, 84121
        • J. Lewis Research, Inc. / Foothill Family Clinic South
      • Salt Lake City, Utah, United States, 84109
        • J. Lewis Research, Inc. / Foothill Family Clinic South

Participation Criteria

Researchers look for people who fit a certain description, called eligibility criteria. Some examples of these criteria are a person's general health condition or prior treatments.

Eligibility Criteria

Ages Eligible for Study

18 years to 40 years (Adult)

Accepts Healthy Volunteers

No

Description

Inclusion Criteria:

Primary Extension Phase:

  • Male and female participants who were CMV-seronegative at the Study mRNA-1647-P202 Screening visit, completed the final Study mRNA-1647-P202 visit, and remained CMV-seronegative at Screening for Study mRNA-1647-P202-EXT.
  • Male and female participants who were CMV-seropositive at the Study mRNA-1647-P202 Screening visit, were randomized to receive mRNA-1647 injection (and not placebo), and completed the final visit in Study mRNA-1647-P202.
  • Understands and agrees to comply with the trial procedures and provides written informed consent.
  • According to the assessment of the Investigator, is in good general health and is capable of complying with trial procedures.

Optional Booster Phase:

For BD Recipients:

- CMV-seronegative and CMV-seropositive participants who received mRNA-1647 medium dose injection (and not placebo or other dose levels) in Study mRNA-1647-P202, including participants who enrolled in the Primary Extension Phase of Study mRNA-1647-P202-EXT and participants who were eligible but did not previously enroll in the Primary Extension Phase of Study mRNA-1647-P202-EXT are eligible to receive a BD in the optional BP.

For Observational Group:

- CMV-seronegative and CMV-seropositive participants who received mRNA-1647 low dose or high dose injection (and not placebo or mRNA-1647 medium dose injection) in Study mRNA-1647-P202, including participants who enrolled in the Primary Extension Phase of Study mRNA-1647-P202-EXT and participants who were eligible but did not previously enroll in the Primary Extension Phase of Study mRNA-1647-P202-EXT are eligible to enroll in the observational group.

Exclusion Criteria:

Primary Extension Phase:

  • Receipt of any CMV vaccine other than mRNA-1647.
  • Diagnosis or condition that, in the judgment of the Investigator, may affect participant safety, assessment of safety endpoints, assessment of immune response, or adherence to trial procedures, including any medical, psychiatric, or occupational condition that, in the opinion of the Investigator, might pose additional risk due to participation in the study or could interfere with the interpretation of study results.

Optional Booster Phase:

For BD Recipients:

- Participants from the placebo, mRNA-1647 low dose, or mRNA-1647 medium dose groups in Study mRNA-1647-P202.

For Observational Group:

- Participants from the placebo or mRNA-1647 medium dose groups in study mRNA-1647-P202.

Note: Other protocol-defined inclusion/exclusion criteria apply

Study Plan

This section provides details of the study plan, including how the study is designed and what the study is measuring.

How is the study designed?

Design Details

  • Primary Purpose: Prevention
  • Allocation: Non-Randomized
  • Interventional Model: Sequential Assignment
  • Masking: None (Open Label)

Arms and Interventions

Participant Group / Arm
Intervention / Treatment
Other: Primary Extension Phase
CMV-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.
Biological: mRNA-1647
No investigational product will be administered during the Primary Extension Phase or to the participants in the Observational Group.
Other: Optional Booster Phase - Observational Group
Participants who opted to enroll into the Observational Group will be followed in the optional BP until BP Month 12.
Biological: mRNA-1647
No investigational product will be administered during the Primary Extension Phase or to the participants in the Observational Group.
Experimental: Optional Booster Phase - BD Recipients
Participants who opted to enroll into the optional Booster Phase will receive a single mRNA-1647 vaccine dose.
Other: mRNA-1647
Lyophilized product that is reconstituted with saline then diluted with a special diluent to reach the desired concentration

What is the study measuring?

Primary Outcome Measures

Outcome Measure
Time Frame
Primary Extension Phase: Geometric Mean Titers (GMTs) of Antigen-Specific Neutralizing Antibody (nAb) and Binding Antibody (bAb)
Time Frame: Up to 3 years
Up to 3 years
BP: GMTs of Antigen-Specific nAb and bAb
Time Frame: BP Month 0, BP Month 1, BP Month 3, BP Month 6, and BP Month 12
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)
Time Frame: Up to BP Day 7 (7 days after BP vaccination)
Up to BP Day 7 (7 days after BP vaccination)
BP: Number of Participants with Unsolicited Adverse Events (AEs)
Time Frame: Up to BP Day 28 (28 days after BP vaccination)
Up to BP Day 28 (28 days after BP vaccination)
BP: Number of Participants with Medically-Attended AEs (MAAEs)
Time Frame: Up to BP Month 6 (6 months after BP vaccination)
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
Time Frame: Up to BP Month 12
Up to BP Month 12

Secondary Outcome Measures

Outcome Measure
Time Frame
Primary Extension Phase: Number of Participants With AEs Leading to Study Discontinuation
Time Frame: Up to 3 years
Up to 3 years
Primary Extension Phase: Number of Participants With SAEs
Time Frame: Up to 3 years
Up to 3 years

Collaborators and Investigators

This is where you will find people and organizations involved with this study.

Sponsor

ModernaTX, Inc.

Study record dates

These dates track the progress of study record and summary results submissions to ClinicalTrials.gov. Study records and reported results are reviewed by the National Library of Medicine (NLM) to make sure they meet specific quality control standards before being posted on the public website.

Study Major Dates

Study Start (Actual)

June 18, 2021

Primary Completion (Actual)

January 19, 2026

Study Completion (Actual)

January 19, 2026

Study Registration Dates

First Submitted

July 9, 2021

First Submitted That Met QC Criteria

July 22, 2021

First Posted (Actual)

July 26, 2021

Study Record Updates

Last Update Posted (Actual)

February 2, 2026

Last Update Submitted That Met QC Criteria

January 30, 2026

Last Verified

January 1, 2026

More Information

Terms related to this study

Keywords

Additional Relevant MeSH Terms

Other Study ID Numbers

  • mRNA-1647-P202-EXT

Drug and device information, study documents

Studies a U.S. FDA-regulated drug product

Yes

Studies a U.S. FDA-regulated device product

No

This information was retrieved directly from the website clinicaltrials.gov without any changes. If you have any requests to change, remove or update your study details, please contact register@clinicaltrials.gov. As soon as a change is implemented on clinicaltrials.gov, this will be updated automatically on our website as well.

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