Comparative Immunogenicity of Concomitant vs Sequential mRNA COVID-19 and Influenza Vaccinations

Inclusion Criteria: * Healthy children aged 6-11 years and healthy adults aged 18-64 years that have not received the current season's influenza vaccination or a mRNA COVID-19 vaccination in the past 6 months and have already completed at least a two-dose primary series of an mRNA COVID-19 vaccination * English or Spanish literate * Email or text message capability for weekly follow-up * Intention of receiving influenza vaccine and mRNA COVID-19 vaccine based on ACIP-CDC guidelines * Willing to provide written/electronic informed consent * Intention of being available for entire study period and able to complete all relevant study procedures, including follow-up phone calls and clinic visits Exclusion Criteria: * Self-reported COVID-19 infection within 3 months prior to enrollment * Received COVID-19 vaccine within 6 months prior to enrollment * Received influenza vaccine during the respective influenza season in which the participants are being enrolled * \< 9 years of age and recommended to receive two doses of IIV4 during the respective influenza season in which they are being enrolled * History of severe allergic reaction after a previous dose of any influenza or COVID-19 mRNA vaccine; or to an influenza or COVID-19 mRNA vaccine component * Receipt of any licensed vaccine within 6 weeks prior to enrollment in this study or planning receipt of any vaccines within 4 weeks after the receipt of the second vaccine dose administered during study procedures * Has an immunocompromising condition or taking immunosuppressive medication\* \* Received oral, intramuscular or intravenous systemic immunosuppressants, or immune modifying drugs for \>14 days in total within 6 months prior to any study vaccine dose (for corticosteroids ≥ 20 mg/day of prednisone equivalent). \*\* Note: Topical medications are allowed * Received immunoglobulin, SARS-CoV-2 immunoglobulin, SARS-CoV-2 monoclonal antibody, or blood-derived products, within 3 months prior any study vaccine dose. * History of Guillain-Barré syndrome * History of myocarditis or pericarditis * History of multisystem inflammatory syndrome in children (MIS-C) or adults (MIS-A) * Currently pregnant, planning to become pregnant within the first three months of the study per participant self-report or likely to be pregnant per screening criteria * Bleeding disorder diagnosed by a healthcare provider or bleeding difficulties with intramuscular injections or blood draws. * Has injury or other reason why deltoid site on both arms cannot be used for vaccinations * Any condition which, in the opinion of the investigators, may pose a health risk to the participant or interfere with the evaluation of the study objectives * Temporary Delay Criteria: History of febrile illness (\> 100.0°F or 37.8°C) within the past 72 hours prior to vaccine administration