• Added electrocardiograms (ECGs), troponin testing, and collection of standard of care clinical data for central review • Additional spirometry measurements collected via handheld devices Study Endpoint and statistical analysis revisions • Inclusion criteria updated to allow subjects ≥ 18 to enroll and to allow PCR positive subjects to be enrolled using an upper or lower respiratory tract sample • Exclusion criteria updated to state that viral co-infection and systemic infection may be allowed if discussed with the medical monitor and deemed acceptable; additional restrictions added as related to sulfa drug response • iADL, ADL, and SF-12 assessments for the Optional Registry will begin at Day 1/Baseline • Edits throughout for clarity and administrative changes were made

• Renumbering as appropriate due to the addition of new sections • Addition of a window for Day 1/Baseline spirometry and the addition of information and clarification on historical spirometry data that should be collected • Updates to pregnancy testing and requirements • Updates to the Study Design schema to include the spirometry window and PK lab draws • Removal of the requirement for safety labs to be collected during the optional registry • Clarification that only procedure-related AEs need to be collected during the optional Extended Viral Monitoring and Optional Registry portions of the study • Clarification that the Day 21 local RSV PCR testing, as required for the optional extended viral monitoring, does not need to be redone if completed for clinical purposes prior to Day 21 with a negative result •Addition of new Phase 1 data •Consolidation of the Prior and Concomitant Medication section