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

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.

Primary Outcome Measures

1. Cohorts 1 and 2: Number of Participants With Solicited Local Adverse Events (AEs)
   Number of participants with solicited local AEs at 7 days post-vaccination in Cohorts 1 and 2 were reported. An AE is any untoward medical occurrence in a participant participating in a clinical study that does not necessarily have a causal relationship with the pharmaceutical/biological agent under study. Solicited local AEs were predefined local events (at the injection site: erythema, pain/tenderness and swelling) that were by definition considered as related to the study vaccine and collected within 7 days after vaccination.
2. Cohorts 1 and 2: Number of Participants With Solicited Systemic AEs
   Number of participants with solicited systemic AEs at 7 days post-vaccination in Cohorts 1 and 2 were reported. An AE is any untoward medical occurrence in a participant participating in a clinical study that does not necessarily have a causal relationship with the pharmaceutical/biological agent under study. Solicited systemic AEs including pyrexia, headache, fatigue, myalgia and nausea were collected within 7 days after vaccination.
3. Cohorts 1 and 2: Number of Participants With Unsolicited AEs
   Number of participants with unsolicited AEs post-vaccination in Cohorts 1 and 2 were reported. An AE was defined as any untoward medical occurrence in a participant participating in a clinical study that did not necessarily have a causal relationship with the pharmaceutical/biological agent under study. Unsolicited AEs were defined as all AEs for which the participant was not specifically questioned in the participant diary.
4. Cohorts 1, 2, and 3: Number of Participants With Serious Adverse Events (SAEs)
   Number of participants with SAEs post-vaccination were reported. An AE was defined as any untoward medical event that occurred in a participant administered an investigational product, and it did not necessarily indicated only events with clear causal relationship with the relevant investigational product. SAE was defined as any AE that resulted in: death, persistent or significant disability/incapacity, required inpatient hospitalization or prolongation of existing hospitalization, was life-threatening experience, was a congenital anomaly/birth defect and would jeopardize participant and/or required medical or surgical intervention to prevent one of the outcomes listed above.
5. Cohorts 1, 2, and 3: Number of Participants With Adverse Events of Special Interest (AESI)
   Number of participants with AESI post-vaccination were reported. AESIs were significant AEs that were judged to be of special interest because of clinical importance, known or suspected class effects, or based on nonclinical signals. Thrombosis with thrombocytopenia syndrome (TTS) was considered as an AESI.
6. Cohorts 1 (Group 1), 2 (Group 3), and 3 (Group 5): Respiratory Syncytial Virus (RSV) A2 Strain Neutralizing Antibody Titers
   RSV A2 strain neutralizing antibody titers of the vaccine-induced immune response was assessed through virus neutralization assay and were expressed as 50% inhibitory concentration (IC50) units.
7. Cohorts 1 (Group 1), 2 (Group 3), and 3 (Group 5): Percentage of Participants With Seroresponse as Assessed by Virus Neutralizing Assay (VNA-A2)
   Percentage of participants with seroresponse as assessed by VNA-A2 strain were reported. Seroresponse was defined as a 4-fold increase from baseline in Day 15 VNA A2 antibody titers.

Secondary Outcome Measures

1. Cohorts 1, 2, and 3: Geomteric Mean Titers (GMTs) of RSV Fusion Protein (F-protein) Antibodies as Assessed by Enzyme-linked Immunosorbent Assay (ELISA)- Pre-Fusion
   GMTs of RSV Fusion Protein (PreF) antibodies as assessed by ELISA-Pre-Fusion at Day 15 were reported.