The main purpose of this study is to evaluate the efficacy of mRNA 1647 vaccine in CMV-seronegative female participants and to evaluate the safety and reactogenicity of mRNA-1647 vaccine in all participants.



Eligible Ages
Between 16 Years and 40 Years
Eligible Genders
Accepts Healthy Volunteers

Inclusion Criteria

  • Participants aged ≥20 years, has or anticipates having direct exposure within 7 months after the planned first dose (in the home, socially, or occupationally) to at least 1 child ≤5 years of age. Direct exposure is defined as either participant is the parent, or participant has close contact (feeding, diaper changes, childcare/supervision) for at least 8 hours per week. - CMV-seronegative Cohort is CMV-seronegative based on CMV testing at Screening. - CMV-seropositive Cohort is CMV-seropositive based on CMV testing at Screening. - Investigator assessment confirms that the participant (including in the case of an emancipated minor), or parent(s)/legally acceptable representative (LAR)(s), as applicable, understand and are willing and physically able to comply with protocol-mandated follow-up including all study visits and procedures anticipated during the 30 month study period. - Female participants of child-bearing potential: Urine pregnancy test is negative at Screening and negative on the day of the first injection (Day 1). If the participant is sexually active with men, has practiced adequate contraception or has abstained from all activities that could result in pregnancy for at least 28 days prior to the first injection (Day 1) and agrees to continue adequate contraception through 3 months following the third study injection (Month 9/Day 257).

Exclusion Criteria

  • History of a diagnosis or condition that, in the judgment of the Investigator, is clinically unstable or may affect participant safety, assessment of safety endpoints, assessment of immune response, or adherence to study procedures. - Received or plans to receive any nonstudy vaccine <28 days prior to and after any study injection; in addition, the following criteria for COVID-19 and influenza vaccines apply: - Any COVID-19 vaccination series must have been completed a minimum 28 days prior to receiving any dose of the study injection. - COVID-19 vaccines (regardless of manufacturer) must be administered at least 28 days prior to or after any study injection. - Influenza vaccines may be administered > 14 days prior to or after any study injection. - Received systemic immunosuppressants or immune-modifying drugs for >14 days in total within 6 months prior to the day of first injection (Day 1) (for corticosteroids, ≥5 milligrams (mg)/day of prednisone equivalent) or plans to do so during the course of the study. Inhaled, nasal, and topical steroids are allowed. Stable immunomodulator regimens used for managing environmental allergies are allowed. - Receipt of an antiviral with activity against CMV (ganciclovir, valganciclovir, foscarnet, cidofovir, letermovir, acyclovir, valacyclovir) <2 weeks prior to the day of first injection or plans to do so during the course of the study. - Previous receipt of an investigational CMV vaccine. - Receipt of systemic immunoglobulins or blood products <3 months prior to the day of first injection. - Participated in an interventional clinical study <28 days prior to the day of first injection (Day 1) or plans to do so while enrolled in this study. - Participant has donated ≥450 milliliters (mL) of blood products <28 days prior to Screening. - Participant is a member of study team or is an immediate family member or household member of study personnel.

Study Design

Phase 3
Study Type
Intervention Model
Parallel Assignment
Primary Purpose
Quadruple (Participant, Care Provider, Investigator, Outcomes Assessor)
Masking Description

Arm Groups

ArmDescriptionAssigned Intervention
Participants will receive mRNA-1647 vaccine by intramuscular (IM) injection on Day 1, Day 57, and Day 169.
  • Biological: mRNA-1647
    Lyophilized product that is reconstituted with 0.9% sodium chloride (normal saline)
Placebo Comparator
Participants will receive mRNA-1647 vaccine matching placebo by IM injection on Day 1, Day 57, and Day 169.
  • Biological: Placebo
    0.9% sodium chloride (normal saline) injection

Recruiting Locations

University of Texas Medical Branch - Bay Colony, SIVS Clinical Trials Program
League City, Texas 77573-1427

More Details

ModernaTX, Inc.

Study Contact

Moderna Clinical Trials Support Center


Study information shown on this site is derived from ClinicalTrials.gov (a public registry operated by the National Institutes of Health). The listing of studies provided is not certain to be all studies for which you might be eligible. Furthermore, study eligibility requirements can be difficult to understand and may change over time, so it is wise to speak with your medical care provider and individual research study teams when making decisions related to participation.