A Study of an Ad26.RSV. preF-based Vaccine in Adults Aged 18 to 59 Years, Including Adults at High Risk for Severe RSV Infection

The purpose of the study is to investigate the safety and immunogenicity of the Ad26.RSV.preF based vaccine in adults 18 to 59 years of age who are healthy or at risk for severe Respiratory Syncytial Virus (RSV) disease, compared to adults 65 years and above.

RSV is an important cause of serious respiratory infections in adults aged 60 years and older, immunocompromised individuals, and those with underlying chronic cardiopulmonary conditions. The current study assess the safety and immunogenicity of the RSV vaccine in adults 18 to 59 years of age, including those who are at risk for severe RSV disease. The study comprises screening (pre-vaccination) and vaccination for each participant on Day 1, and a 6- month safety and immunogenicity follow-up period. The study duration will be up to 6 months per participant. Assessments like immunogenicity (such as humoral and cellular immune responses), safety (such as monitoring of AEs, physical examinations, and vital signs) and reactogenicity will be performed in this study.

Eligibility Criteria:
Inclusion Criteria:

* Participants must be of a) non child bearing potential or b) of child bearing potential and practicing an acceptable and effective of contraception
* All participants of childbearing potential must: have a negative highly sensitive urine beta-human chorionic gonadotropin (beta-hCG) pregnancy test at screening; and have a negative highly sensitive urine beta-hCG pregnancy test immediately prior to each study vaccination (if screening and vaccination are not performed on the same day) Cohorts 1 and 2
* Participant is aged 18 to 59 years (inclusive) on the day of signing the informed consent form (ICF) and expected to be available for the duration of the study Cohort 2
* Has an existing chronic heart or lung condition, without hospitalizations or major medication class change (that is, new or stopped medications) within 30 days prior to screening, meeting the following criteria; a) cardiac disease: at least Class II symptoms per New York Heart Association classification or similar guidelines according to local practice, b) pulmonary disease: activity-restricting symptoms or use of long-term medications Cohort 3
* Participant is aged 65 years or older on the day of signing the ICF and expected to be available for the duration of the study
* Participant may have underlying illnesses such as hypertension, congestive heart failure, chronic obstructive pulmonary disease (COPD), type 2 diabetes, hyperlipoproteinemia, or hypothyroidism, as long as their symptoms and signs are stable at the time of vaccination, and these conditions receive routine follow-up by the participant's healthcare provider

Exclusion Criteria:

* Known or suspected allergy or history of anaphylaxis or other serious adverse reactions to vaccines or their excipients (including specifically the excipients of the study vaccine)
* Abnormal function of immune system due to a clinical condition or treatment
* History of thrombosis with thrombocytopenia syndrome (TTS) or heparin-induced thrombocytopenia and thrombosis (HITT).
* Participant received or plans to receive: (a) licensed live attenuated vaccines - within 28 days before or after planned administration of study vaccine; and (b) other licensed (not live) vaccines - within 14 days before or after planned administration of study vaccine
* Received an respiratory syncytial virus (RSV) vaccine in a previous RSV vaccine study
* History of acute polyneuropathy (example, Guillain-Barre syndrome) or chronic idiopathic demyelinating polyneuropathy