Clinical Core Principal Investigator: Asuncion Mejias, M.D. Abstract This Core will serve three main goals. First, by enrolling all patients, obtaining the human samples, and collecting the clinical data it will simplify sample organization, data management and compliance with all regulatory aspects of the U19. In addition, the Clinical Core will support Projects 1 and 2, by performing the viral PCR assays, which will improve analytical performance and efficiency; and the Data Management Core, by coordinating and sharing de-identified clinical data. Specifically, the Core will be responsible for: 1) enrolling infants in the first 6 months of life with influenza or SARS-CoV-2 infection, as well as healthy non-infected controls, and obtaining sequential blood and respiratory samples pre and post influenza and COVID-19 vaccination during the first 3 years of life; 2) sample organization and distribution between Projects (1 and 2); 3) longitudinal clinical data collection, data curation and data transfer to the Data Management Core for data analyses and integration with all immune assays; 4) measure influenza and SARS-CoV-2 viral loads by quantitative real-time PCR in clinical samples (nasopharyngeal swabs) from infants with influenza or SARS-CoV-2 infection. This approach will optimize the use of resources and will facilitate integration and synergy among all projects.