This is a human challenge sequential cohort study involving healthy, non-smoking older adults aged 65-75 years. We aim to enrol 20 participants. There will be a sentinel cohort of 6 participants at the beginning of the study (Group 1). If no pausing rules are met, the remaining 14 participants will be enrolled for a total of 20 enrolled participants (Group 2).
The study will consist of three main phases: (1) screening and baseline, (2) inoculation and quarantine, and (3) follow up.
All participants will attend a screening visit for a comprehensive health assessment to confirm eligibility.
If eligible, participants will take part in an inpatient stay in a quarantine unit, where they will be inoculated with 105 plaque-forming units of RSV B-I54 by intranasal drops. The inoculation dose has been determined in the earlier mentioned outpatient study of the same virus strain, in healthy young adults.
Due to the older age range and potentially increased risk of more severe disease, participants will remain within the quarantine unit for 10-days post inoculation and will be closely monitored by clinical review and self-completed symptom diaries. Participants will undergo daily sample collection and will remain in quarantine until the discharge criteria are met at Day 10.
After discharge, participants will attend follow-up visits at Day 14, Day 28, and Day 90.
Participants in Group 2 will have an additional baseline visit at Day -14 where blood, respiratory (nose and throat) and lower airway (bronchoscopy) samples will be collected. Group 2 participants will also undergo a second bronchoscopy during the inpatient period and the third and final bronchoscopy at Day 28.
Clinical outcomes will be determined by symptomatology and viral detection in nasal lavage using quantitative PCR. Based on the first-in-human RSV B characterisation study and recent elderly RSV A challenge data, we anticipate approximately 74% attack rate, with a range of mild-moderate symptoms in the infected individuals. Symptoms typically commence 3 days post-inoculation and worsen to peak around days 5-9 before rapidly resolving without treatment. Timing of viral shedding is expected to correlate closely with symptoms.