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Evaluating an mRNA vaccine for cytomegalovirus in young participants

A Phase 1/2a Open-Label Dose-Ranging and Observer-Blind Placebo-Controlled, Safety and Immunogenicity Study of mRNA-1647 Cytomegalovirus Vaccine in Female and Male Participants 9 to 15 Years of Age and Participants 16 to 25 Years of Age

Phase1; Phase2 Interventional ModernaTX, Inc. · NCT05575492

This study is testing a new mRNA vaccine for cytomegalovirus in healthy young people aged 9 to 25 to see if it's safe and helps their immune system.

Quick facts

PhasePhase1; Phase2
Study typeInterventional
Enrollment770 (estimated)
Ages9 Years to 25 Years
SexAll
SponsorModernaTX, Inc. Industry-sponsored
Drugs / interventionsprednisone
Locations71 sites (Birmingham, Alabama and 70 other locations)
Trial IDNCT05575492 on ClinicalTrials.gov

What this trial studies

This study aims to assess the safety and immune response of the mRNA-1647 vaccine in healthy participants aged 9 to 25 years, focusing on both CMV-seronegative and CMV-seropositive individuals. The research is divided into two parts: a dose-ranging phase and a safety expansion phase. Participants will receive either the mRNA-1647 vaccine or a placebo, and their health will be monitored throughout the study to evaluate the vaccine's effectiveness and safety profile.

Who should consider this trial

Good fit: Ideal candidates include healthy males and females aged 9 to 25 years who are either CMV-seronegative or CMV-seropositive.

Not a fit: Patients with isolated positive or indeterminate results for CMV IgM or indeterminate results for CMV IgG will not benefit from this study.

Why it matters

Potential benefit: If successful, this vaccine could provide effective protection against cytomegalovirus in young individuals.

How similar studies have performed: Other studies involving mRNA vaccines have shown promising results, indicating potential success for this approach.

Eligibility criteria

Show full inclusion / exclusion criteria 
Key Inclusion Criteria:

* Is a female or male 9 to 15 years of age or is a female 16 to 25 years of age at the time of consent.
* Is in good general health, in the opinion of the Investigator, and is capable of complying with study procedures.
* For the CMV-seronegative cohorts: At the Screening visit, is CMV IgG-negative and CMV immunoglobulin M (IgM)-negative.
* For CMV-seropositive cohorts: At the Screening visit, is CMV IgG-positive and CMV IgM-negative, CMV IgG-positive and CMV IgM-positive, or CMV IgG-positive and CMV IgM-indeterminate. Participants with an isolated positive or indeterminate result for CMV IgM (that is, CMV IgG-negative and either CMV IgM-positive or CMV IgM-indeterminate) will not be eligible for enrollment but may be rescreened after at least 6 weeks from the initial CMV Screening. Participants with an indeterminate result for CMV IgG, regardless of IgM result, will not be eligible for enrollment but may be rescreened after at least 6 weeks from the initial CMV screening.
* If 9 to 15 years of age, has a body mass index (BMI) at or above the third percentile according to World Health Organization (WHO) Child Growth Standards. If 16 to 25 years of age: has a BMI of 15 to 35 kilograms (kg)/square meter (m\^2).
* For female participants of childbearing potential: negative pregnancy test, adequate contraception or has abstained from all activities that could result in pregnancy for at least 28 days prior to Day 1, agreement to continue adequate contraception through 3 months following vaccine administration.

Key Exclusion Criteria:

* Has a history of a diagnosis or condition that, in the judgment of Investigator, is clinically unstable or may affect participant safety, assessment of safety endpoints, assessment of immune response, or adherence to study procedures. Clinically unstable is defined as diagnosis or condition requiring significant changes in management or medication within the 2 months prior to Screening and includes ongoing workup of an undiagnosed illness that could lead to a new diagnosis or condition.
* Has received, or plans to receive, any nonstudy vaccine \< 28 days prior to or after any study injection.
* Has a screening liver function test (aspartate aminotransferase, alanine aminotransferase, total bilirubin) or a screening creatinine result of Toxicity Grade ≥1.
* Has a Screening hematology or coagulation result of Toxicity Grade ≥1.
* Is acutely ill or febrile (body temperature ≥38.0 degrees Celsius \[°C\]/100.4 degrees Fahrenheit \[°F\]) at the Screening Visit.
* Has received systemic immunosuppressants or immune-modifying drugs for \> 14 days in total within 6 months prior to the day of enrollment (for corticosteroids, ≥1 milligrams (mg)/kg/day or ≥10 mg/day prednisone equivalent).
* Has received an antiviral with activity against CMV (ganciclovir, valganciclovir, foscarnet, cidofovir, letermovir, acyclovir, valacyclovir) \<2 weeks prior to the day of the first study injection (Day 1) or plans to do so during the course of the study.
* Reports a history of myocarditis, pericarditis, or myopericarditis.
* Has reported medical history of hepatitis B, hepatitis C, or human immunodeficiency virus (HIV); or a positive screening test for hepatitis B surface antigen (HBsAg), hepatitis C antibodies, or HIV 1 or 2 antibodies.
* Has previously received an investigational CMV vaccine.
* Has received systemic immunoglobulins or blood products \<3 months prior to the day of the first study injection (Day 1).
* Has donated ≥ 450 milliliter (mL) of blood products \<28 days prior to the day of the first study injection (Day 1).
* Has participated in an interventional clinical study \<28 days prior to the day of the first study injection (Day 1) or plans to do so while enrolled in the study.

Note: Other inclusion and exclusion criteria may apply.

Where this trial is running

Birmingham, Alabama and 70 other locations

+21 more sites — see ClinicalTrials.gov for the full list.

Study contacts

How to participate

  1. Review the eligibility criteria above with your treating physician.
  2. Visit the official trial page on ClinicalTrials.gov for the most current contact information and recruitment status.
  3. Contact the listed study coordinator or principal investigator to request pre-screening. Pre-screening is free and never obligates you to enroll.
View on ClinicalTrials.gov → Find more trials like this →
Conditions CytomegalovirusmRNA-1647 VaccineCMVModerna
Last reviewed 2026-06-13 by the Find a Trial editorial team. Information on this page is for educational purposes and is not medical advice. Always consult qualified healthcare professionals about clinical trial participation.