• Participants, who, in the opinion of the investigator, can and will comply with the requirements of the protocol (e.g., completion of the diary cards, return for follow-up visits). Note: In case of physical incapacity that would preclude the self-completion of the diary cards, either site staff can assist the participant (for activities performed during site visits) or the participant may assign a caregiver to assist him/her with this activity (for activities performed at home). However, at no time will the site staff or caregiver evaluate the participant's health status while answering diaries or make decisions on behalf of the participant. - Written or witnessed informed consent obtained from the participant (participant must be able to understand the informed consent) prior to performance of any study-specific procedure. - A male/female of ≥50 Years of age (YOA) at the time of the first study intervention administration. - Participants who are medically stable in the opinion of the investigator at the time of first vaccination. Participants with chronic stable medical conditions with or without specific treatment, such as diabetes, hypertension or cardiac disease, are allowed to participate in this study if considered by the investigator as medically stable. A stable medical condition is defined as disease not requiring significant change in therapy or hospitalization for worsening disease during the 3 months before enrollment. • Participants living in the general community or in an assisted-living facility that provides minimal assistance, such that the participant is primarily responsible for self-care and activities of daily living. Participants who have received previously a SARS-CoV-2 vaccine, being administered at least 3 months prior to study vaccination. - Female participants of non-childbearing potential may be enrolled in the study. Non childbearing potential is defined as hysterectomy, bilateral oophorectomy, bilateral salpingectomy, and post-menopause. - Female participants of childbearing potential may be enrolled in the study if the participant. - has practiced adequate contraception from 1 month prior to study intervention administration and agreed to continue adequate contraception for at least 1 month after the last vaccination. - has a negative pregnancy test on the day of and prior to study intervention administration.

Medical Conditions - History of any reaction or hypersensitivity likely to be exacerbated by any component of the study interventions, including a known history of severe allergic reaction (e.g., anaphylaxis). - Any confirmed or suspected immunosuppressive or immunodeficient condition, resulting from disease (e.g., current malignancy, human immunodeficiency virus) or immunosuppressive/cytotoxic therapy (e.g., medication used during cancer chemotherapy, organ transplantation, or to treat autoimmune disorders), based on medical history and physical examination (no laboratory testing required). - Any history of myocarditis or pericarditis. - Recurrent history or uncontrolled neurological disorders or seizures. Participants with medically-controlled active or chronic neurological diseases can be enrolled in the study as per investigator assessment, provided that their condition will allow them to comply with the requirements of the protocol (e.g. completion of diary cards, attend regular phone calls/study site visits). - Serious or unstable chronic illness. - Any history of dementia or any medical condition that moderately or severely impairs cognition. - Significant underlying illness that in the opinion of the investigator would be expected to prevent completion of the study (e.g., life-threatening disease likely to limit survival up to study end). - Any medical condition that in the judgment of the investigator would make intramuscular injection unsafe. - Any SAE attributed to a previous dose of the SARS-CoV-2 mRNA vaccine. - Any other clinical condition that, in the opinion of the investigator, might pose additional risk to the participant due to participation in the study. - Recent SARS-CoV-2 infection within 3 months prior to the COVID-19 vaccine dose administration. Timelines to be determined from symptoms onset or positive COVID-19 test (if infection was asymptomatic). Prior/Concomitant Therapy Use of any investigational or non-registered product (drug, vaccine or invasive medical device) other than the study interventions during the period beginning 30 days before the first dose of study interventions and ending 30 days after the last vaccine administration, or their planned use during the study period. - Planned administration of a vaccine in the period starting 30 days before the first dose and ending 30 days after the last dose of study intervention(s) administration*, with the exception of inactivated and subunit influenza vaccines which can be administered up to 14 days before or from 14 days after the study vaccination. *If emergency mass vaccination for an unforeseen public health threat (e.g., a pandemic) is recommended and/or organized by public health authorities outside the routine immunization program, the time period described above can be reduced if necessary for that vaccine, provided it is used according to the local governmental recommendations and Sponsor is notified. - Chronic administration of immune-modifying drugs (defined as more than 14 consecutive days in total) and/or planned use of long-acting immune-modifying treatments at any time up to the last blood sampling visit. - Up to 3 months prior to the study intervention administration: - For corticosteroids, this will mean prednisone equivalent ≥ 20 mg/day. Inhaled and topical steroids are allowed. - Administration of immunoglobulins and/or any blood products or plasma derivatives. - Up to 6 months prior to study intervention administration: long-acting immune modifying drugs including among others immunotherapy (e.g., TNF-inhibitors), monoclonal antibodies and antitumoral medication. - Administration of any SARS-CoV-2 vaccine during the 3 months preceding the study COVID-19 mRNA vaccine administration. - Previous vaccination with licensed or investigational RSV vaccine. 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 (drug/invasive medical device). Other Exclusion Criteria - Pregnant or lactating female participant. - Female participant planning to become pregnant or planning to discontinue contraceptive precautions. - History of chronic alcohol consumption and/or drug abuse as deemed by the investigator to render the potential participant unable/unlikely to provide accurate safety reports or comply with study procedures. - Participation of any study personnel or their immediate dependents, family, or household members. - Planned move during the study conduct that prohibits participation until study end. - Bedridden participants.