A Study on the Immune Response and Safety of Vaccine Against Respiratory Syncytial Virus (RSV) Given to Adults 18 to 49 Years of Age at Increased Risk for Respiratory Syncytial Virus Disease, Compared to Older Adults 60 Years of Age and Above

Inclusion Criteria

• Participants and/or participant's parent(s)/ Legally acceptable representative (LAR) who, in the opinion of the investigator, can and will comply with the requirements of the protocol (e.g., completion of the eDiary, attend study site visits, ability to access and utilize a phone or other electronic communications).
• Written or witnessed informed consent obtained from the participant/participant's parent(s)/LAR(s) (participant must be able to understand the informed consent) prior to performance of any study-specific procedure.

Written informed assent obtained from the participant (participant must be able to understand the informed assent) if he/she is less than the legal age prior to performance of any study-specific procedure.

Specific inclusion criteria for all participants in Cohort 1 and Cohort 3 (RSV-A-AIR Group) • A male or female participant 18-49 YOA at the time of the study intervention administration.

• Participants should be diagnosed with at least 1 of the following medical conditions if considered medically stable by the investigator:
• Chronic cardiopulmonary disease resulting in activity restricting symptoms or use of long term medication:

o Chronic obstructive pulmonary disease (COPD)

o Asthma

o Cystic fibrosis

o Other chronic respiratory diseases: lung fibrosis, restrictive lung disease, interstitial lung disease, emphysema or bronchiectasis

o Chronic heart failure:

o Pre-existing Coronary Artery Disease (CAD) (CAD not otherwise specified)

• Cardiac arrhythmia
• Diabetes mellitus: types 1 or 2 with active treatment for the past 6 months
• Other diseases at increased risk for RSV disease:
• Chronic kidney disease
• Chronic moderate to severe liver disease
• Neurologic or neuromuscular conditions
• Female participants of non-childbearing potential may be enrolled in the study. Non-childbearing potential is defined as premenarche, 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 study prior to intervention administration, and
• has agreed to continue adequate contraception for at least 1 month after completion of the study intervention administration.

Specific inclusion criteria for all participants in Cohort 2 (RSV-OA Group):

• A male or female participant >=60 YOA at the time of the study intervention administration.

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 medically stable by the investigator.

• 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.

Exclusion Criteria

Medical conditions

• 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).
• History of any reaction or hypersensitivity likely to be exacerbated by any component of the study intervention.
• Unstable chronic illness.
• Any history of dementia or any medical condition that moderately or severely impairs cognition.
• Recurrent 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 protoc