Summary: This study consists of two parts: Part A Surveillance and Part B Transmission. The main purpose of Part A is to evaluate the prevalence of pre-dose and treatment-emergent amino acid substitutions in pediatric participants' susceptibility \<12 years with influenza treated with baloxavir marboxil. Part B will include a subset of Part A participants who have household contacts (HHCs) recruited to the...

Summary: This phase II trial studies the effect of baloxavir in combination with oseltamivir in treating severe influenza infection in patients who have previously received a hematopoietic (blood) stem cell transplant or have a hematological malignancy. Baloxavir is an antiviral drug that inhibits the growth of influenza virus, reduces viral load and prevents further influenza infection. Osetamivir is an a...

Summary: The purpose of this clinical trial is to find out if the medication called baloxavir marboxil (sold under the brand name Xofluza®) can help to reduce the time needed to recover from flu when patients need an hospitalization. Patients infected by influenza and requiring a hospitalization will be approched to be included in the study. The main questions are: 1. When someone is hospitalized with a se...