Simultaneous mRNA COVID-19 and IIV4 Vaccination Study

This study is a prospective, randomized clinical trial. During this study, participants will be randomly assigned to receive quadrivalent inactivated influenza vaccine (IIV4) and mRNA COVID-19 vaccine either simultaneously or sequentially, 7-14 days apart. Persons in the simultaneous group will receive mRNA COVID-19 and IIV4 at Visit 1 (Day 1) and a saline placebo injection at Visit 2. Persons in the sequential group will receive mRNA COVID-19 vaccine and a saline placebo at Visit 1 (Day 1) and IIV4 injection at Visit 2. For participants receiving their primary dose series, a second dose of mRNA COVID-19 vaccine will be administered either 3 to 8 weeks or 4 to 8 weeks following the first dose, depending upon the mRNA COVID-19 vaccine provided. For those receiving a booster dose of mRNA COVID-19 only a single mRNA COVID-19 will be received in this study. Solicited symptoms of reactogenicity and adverse events will be assessed on vaccination day and daily during the 7 days following each Vaccination Visit using either electronic or paper symptoms diaries, depending on study participant preference. Quality of life data will be collected using electronic or paper diaries on day of Vaccination Visit 1 and daily during the 7 days following the visit. Serious adverse events and adverse events of special interest will be collected throughout the duration of the study. Participants are followed through Day 121. Serum samples from participants will be collected for determination of SARS-CoV-2 seropositivity at baseline. Serum samples will be taken throughout the study to determine IIV4 and COVID-19 vaccine immunogenicity and for potential future studies.