Inclusion Criteria:  Participants who, in the opinion of the investigator, can and will comply with the requirements of the protocol. Written informed consent obtained from the participant prior to performance of any study specific procedure. A healthy adult (woman or man), 18 to 50 years of age at the time of the first study intervention administration. Healthy participants as established by medical history and clinical examination before entering the study. Participants who are women of non-childbearing potential may be enrolled in the study.  Participants who are women of child-bearing potential may be enrolled in the study, if the participant:  has practiced adequate contraception for 30 days prior to study intervention administration, and has a negative pregnancy test on the day of study intervention administration and has agreed to continue adequate contraception during the entire treatment period and for 3 months after completion of the study intervention administration series. Participants who agree to take appropriate infection control measures to prevent becoming infected with SARS-CoV2 during the study. Participants who initially fail screening due to COVID-19 infection may be re-screened and included in the study, within the screening window period. Participants who are diagnosed with COVID-19 may receive their subsequent CMVsu vaccination dose provided they have no fever, and their condition is considered stable by the investigator (e.g. there may be mild lingering cough, but no shortness of breath or difficulty breathing) within 30 days of the original schedule. Participants who initially fail screening due to other active infections may be re screened within the screening window period and included in the study, if they no longer have signs or symptoms of active infection in the judgment of the site investigator. If a participant has equivocal results on CMV diagnostic ELISA screening, they are permitted to be re-screened if within the 28-day screening window. Flexibility in safety blood evaluations will be permitted within the Schedule of activities time intervals.  Exclusion Criteria:  Medical conditions  Known documented medical history of human immunodeficiency virus or viral hepatitis B or C infection. History of any reaction or hypersensitivity likely to be exacerbated by any component of the study intervention(s). Any confirmed or suspected immunosuppressive or immunodeficient condition, based on medical history and physical examination. Family history of congenital or hereditary immunodeficiency. History of or current autoimmune disease. Lymphoproliferative disorder or malignancy within previous 5 years (excluding effectively treated non-melanotic skin cancer). Hypersensitivity to latex. Major congenital defects, as assessed by the investigator. Acute or chronic clinically significant pulmonary, cardiovascular, hepatic or renal functional abnormality, as determined by physical examination or laboratory screening tests. Recurrent history or uncontrolled neurological disorders.  Any hematological or biochemical abnormality*.  *Participants with Food and Drug Administration (FDA) toxicity Grade 1 differential cell counts and considered not clinically significant may be enrolled at the discretion of the investigator, and with the review and approval of the medical monitor. Participants with hematological / biochemical values out of normal range which are not clinically significant and expected to be temporary may be re-screened within the allowed window period. Any acute or chronic, clinically significant disease, as determined by physical examination or laboratory screening tests. Any medical condition that in the judgment of the investigator would make intramuscular injection unsafe. Participants with symptoms suggestive of active COVID-19 infection are excluded. Participants with known COVID-19 positive contacts within the past 14 days should be excluded for at least 14 days since the exposure and the participant remains symptom free. Any other clinical condition that, in the opinion of the investigator, might pose additional risk to the participant due to participation in the study.  Prior/Concomitant therapy  Any history of or planned receipt of a CMV vaccine other than the study intervention (CMVsu) at any time point. Use of other investigational or non-registered product during the period beginning 30 days before the first dose, or their planned use during the study period. Planned administration or administration of any vaccine not foreseen by the study protocol 30 days before and 30 days after each study vaccination administration, with the exception of any licensed influenza vaccine which may be administered > 15 days before or after vaccination.  In case of emergency mass vaccination for an unforeseen public health threat) organized by public health authorities outside the routine immunization program, the time period can be reduced if necessary, for that mass vaccination vaccine, which may be under emergency use authorization.  COVID-19 vaccines should be given at least 30 days before or after administration of a GSK study vaccine. However, this interval can be reduced to > 14 days, if emergency vaccination is recommended by public health authorities, in line with the applicable local/national guidance per COVID-19 vaccine platform type under emergency use authorization. Candidate COVID-19 vaccines that have not received limited, accelerated, or full authorization, and are only in use as part of a clinical trial, are not allowed. Chronic administration of immunosuppressants or other immune-modifying drugs within 3 months prior to the vaccine dose. Inhaled and topical steroids are allowed. Administration of long-acting immune-modifying drugs at any time during the study period. Administration of immunoglobulins and/or any blood products during the period starting 3 months before the administration of the first dose of study intervention(s) or planned administration during the study period.  Prior/Concurrent clinical study experience  • Concurrently participating in another clinical study, at any time during the study period, in which the participant has been or will be exposed to an investigational or a non-investigational intervention  Other exclusions  Pregnant or lactating women. If a woman becomes pregnant/lactating during the study, she will be excluded from subsequent vaccine doses but will be followed for safety. Women planning to become pregnant or planning to discontinue contraceptive precautions before 3 months after last study vaccination. Participants with known high exposure risk for CMV transmission, to enable distinction of true vaccine effect from natural infection during the study. Planned move to a location that will prohibit participating in the trial until study end. Participants with current chronic alcohol consumption and/or drug abuse as defined by Diagnostic and Statistical Manual of Mental Disorders 5th edition.