A Surveillance Study of Susceptibility to Baloxavir Marboxil in Participants With Influenza (Pebblestone)

Inclusion Criteria: Participants with symptoms suggestive of influenza 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. The time interval between the onset of influenza symptoms and the pre-dose examinations at screening is 48 hours or less Exclusion Criteria: Participants with severe influenza virus infection requiring inpatient treatment. Severely immunocompromised participants [including participants receiving immunosuppressant therapy, or those with cancer or human immunodeficiency virus (HIV) infection] as defined by the investigator. Participants with concurrent (non-influenza) infections requiring systemic anti-microbial and/or anti-viral therapy at the pre-dose examinations. Treatment with baloxavir marboxil, peramivir, laninamivir, oseltamivir, zanamivir, rimantadine, umifenovir or amantadine within 30 days prior to screening. Treatment with an investigational influenza-specific monoclonal antibody within 6 months or 5 half-lives, whichever is longer, prior to screening. Treatment with an investigational therapy within 30 days or 5 half-lives, whichever is longer, prior to screening. Known hypersensitivity to baloxavir marboxil or the drug product excipients. Females who have commenced menarche (i.e., child-bearing potential).