Inclusion Criteria:
Participants, who, in the opinion of the investigator, can and will comply with the requirements of the protocol.
• 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.
Specific inclusion criteria for all participants in Cohort 1 (Older adults)
* Male or female, \>= 60 YOA at the time of the study intervention administration.
* Participants who are medically stable in the opinion of the investigator at the time of study intervention administration. Participants with chronic stable medical conditions with or without specific treatment, such as diabetes mellitus, hypertension, or cardiac disease, are allowed to participate in this study if considered by the investigator as medically stable.
* Participants living in the general community or in an assisted-living facility that provides minimal assistance can be enrolled, such that the participant is primarily responsible for self-care and activities of daily living.
Specific inclusion criteria for all participants in Cohort 2 (Adults-AIR)
* Male or female, 50-59 YOA at the time of the study intervention administration.
* Participants should be diagnosed with at least 1 of the following medical conditions and considered medically stable by the investigator:
* Chronic pulmonary disease resulting in activity restricting symptoms or use of long term medication:
* Chronic obstructive pulmonary disease (COPD)
* Asthma
* Cystic fibrosis
* Other chronic respiratory diseases: lung fibrosis, restrictive lung disease, interstitial lung disease, emphysema, or bronchiectasis
* Chronic cardiovascular disease:
* Chronic heart failure (CHF)
* Pre-existing coronary artery disease (CAD not otherwise specified)
* Cardiac arrhythmia
* Diabetes mellitus: type 1 or type 2
Other diseases at increased risk for RSV-LRTD disease:
* Chronic kidney disease
* Chronic liver disease
* Female participants of non-childbearing potential may be enrolled in the study. Non childbearing potential is defined as hysterectomy, bilateral oophorectomy, bilateral salpingectomy, or 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
* has a negative pregnancy test on the day of and prior to study intervention administration, and
* has agreed to continue adequate contraception for at least 1 month after the study intervention administration.
Exclusion Criteria:
Medical Conditions
* History of any reaction or hypersensitivity likely to be exacerbated by any component of the study interventions.
* 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).
* Unstable chronic illness.
* 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 the eDiary, attend phone call/study site visits).
* 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).
* Any medical condition that in the judgment of the investigator would make intramuscular injection unsafe.
* 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
* 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 (Day -29 to Day 1) before the dose of study interventions or their planned use during the study period (Day 1 up to Month 6).
* Previous vaccination with licensed or investigational RSV vaccine. Planned or actual administration of a vaccine not foreseen by the study protocol in the period starting 30 days before and ending 30 days after the dose of study intervention administration, with the exception of inactivated, subunit and split influenza vaccines or COVID-19 vaccines (fully licensed or with emergency use authorization \[EUA\]) which can be administered up to 14 days before or from 14 days after the study intervention administration.
* 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 end of the study.
* Up to 3 months prior to the study intervention administration:
* For corticosteroids, this will mean prednisone equivalent \>= 20 mg/day for adult participants. 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, antitumoral medication.
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 for all participants
* 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.
Other Exclusion Criteria for cohort 2 (Adults-AIR)
* Pregnant or lactating female participant.
* Female participant planning to become pregnant or planning to discontinue contraceptive precautions.
