A Study to Evaluate the Safety, Tolerability, and Immunogenicity of a Combined Modified RNA Vaccine Candidate Against COVID-19 and Influenza.

The purpose of this study is to understand the safety and effects of a combined influenza and COVID-19 vaccine. This combined vaccine is compared to separate vaccines for the protection against influenza and SARS-CoV-2. Influenza and COVID-19 are diseases that can spread easily from one person to another and cause body aches, fever, cough, and other symptoms. Giving both influenza and COVID-19 vaccines together against influenza and SARS-CoV-2 could provide great benefits to both patients and caregivers in terms of simple and easy care. Around 8550 participants will be assigned into 1 of 8 vaccination groups (Group A, B, C, D, E, F, G or H) by chance.

Cohort 1: Approximately 450 participants will be assigned by chance to one of the following:

• Group A:Influenza and COVID-19 combination A vaccine, given at the same time in one arm and placebo (an injection consisting of just salt water and no medicines in it) in the opposite arm.

• Group B: COVID-19 vaccine, given at the same time to one arm and licensed influenza vaccine in the opposite arm.

Cohort 2: Approximately 4500 participants will be assigned by chance to one of the following:

• Group C: Influenza and COVID-19 combination B vaccine, given at the same time in one arm and placebo in the opposite arm.

• Group D: COVID-19 vaccine, given at the same time in one arm and licenced influenza vaccine in the opposite arm.

Cohort 3: Approximately 3600 participants will be assigned by chance to one of the following:

• Group E: Influenza and COVID-19 combination B vaccine.

• Group F: COVID-19 vaccine.

• Group G: Licenced influenza vaccine.

• Group H: Investigational influenza vaccine.

All participants in cohort 1 and cohort 2 will receive 2 injections and participants in cohort 3 will receive 1 injection as per their assigned study group at Visit 1. The participants will be followed for about 6 months. During this time, researchers will assess safety and the body's reaction to the vaccination over approximately 6 months. This will help understand if the study medicine is safe.