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