A Surveillance Study of Susceptibility to Baloxavir Marboxil in Pediatric Participants With Influenza and Transmission of Influenza to Household Contacts

Inclusion Criteria

• •Participants with symptoms suggestive of influenza based on investigator's judgement with diagnosis confirmed by a positive local influenza test within 24 hours before full study screening
• •Participants with a negative severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) test within 48 hours before full study screening
• •Time interval between onset of influenza symptoms and the pre-dose examinations at screening is 48 hours or less
• •\[A\] IP:
• •Eligible to take part in Part A
• •Lives in a household with a HHC willing to be recruited as full household contact
• •\[B\] HHCs:
• •\- Each HHC living in the home of an IP at the time of IP treatment must be screened for partial or full-study HHC eligibility
• •\[C\] Partial HHC:
• •Starts screening within 1 calendar day after IP treatment
• •Negative influenza and SARS-CoV-2 test at screening after IP's treatment with baloxavir marboxil
• •HHC lives in a household where 1 or more HHCs meet the full-study HHC requirements AND at least 1 full-study HHC has not received the influenza vaccine within 6 months prior to screening
• •HHC lives in a household where 1 or more HHCs meet the full-study HHC requirements AND at least 1 full-study HHC has not received the influenza vaccine within 6 months prior to screening.
• •HHC lives with other HHCs (if applicable) who fulfill all the "Partial household contact" criteria
• •\[D\] Full-study HHC:
• •Fulfills the "Partial household contact" criteria
• •Agrees to participate in the full study
• •Will reside in the IP's house for at least 12 of the next 15 days and will be present for scheduled study visits
• •No influenza symptoms within 7 days prior to screening
• •Does not have a moderate or worse active infections OR infections requiring systemic or otherwise internally administered or otherwise internally administered antibiotic/antiviral/antifungal therapy