Study of a Combination Vaccine Comprised of Different Recombinant Spike Antigen Levels of a Matrix-M Adjuvanted Recombinant COVID-19 Vaccine and High-Dose Inactivated Influenza Vaccine in Adult Participants 50 Years of Age and Older

Study VBT00001 is planned to be a Phase 1/2, randomized, modified double-blind, active-controlled, multi-center study to be conducted in approximately 980 adults aged 50 years and older in the United States. The purpose of the study is to assess the safety and immunogenicity of IIV-HD (high-dose inactivated influenza vaccine) + rC19 (adjuvanted recombinant COVID-19 vaccine) vaccine comprised of IIV-HD combined with different recombinant Spike (rS) antigen levels of rC19 compared to IIV-HD alone, rC19 (dose 1) alone, and IIV-HD and rC19 (dose 1) (coadministered in opposite arms). Placebo will be coadministered in the IIV-HD alone, rC19 (dose 1) alone, and IIV-HD + rC19 study groups to control for the number of injections and to maintain observer-blinding. Thus, each participant will receive two injections at enrollment, one in each deltoid muscle. Study details include: * The study duration will be approximately 12 months * Study intervention will be administered via a single intramuscular (IM) injection into the right and left deltoid muscles on D01 * Dose escalation with sequential enrollment (sentinel cohort followed by main cohort for a given dose) * The visit frequency will be D01, D09 (telephone call), D30, D182 (telephone call), and D366 (telephone call) Number of Participants: Approximately 980 participants are expected to be randomized.