PF-07941314

Substudy A: The study aims to learn about the safety and effects of two new vaccines for RSV (RSVpreF) and influenza (modRNA qIRV) when given as a single shot compared to when given separately. RSV and influenza lead to infections, mainly in the fall and winter. These vaccines are being developed to help prevent respiratory syncytial virus (RSV) and influenza (Flu) disease.
This study is seeking participants who:
* are 60 years or older
* are healthy or have well-controlled chronic conditions
* have not had a flu shot in the last 120 days
* and agree to be present for all study visits, procedures, and blood draws.
The participants will be divided into 2 groups. Group 1 will receive RSVpreF plus qIRV combo shot, after which participants will receive the placebo (a shot which has no medicine). Group 2 will receive shots for qIRV first and then RSVpreF 1 month apart.
The investigators will examine the experiences of the participants receiving the study vaccines. This will help the investigators determine if the study vaccines are safe and produce a similar immune response.
Participants will be involved in this study for 2 months. During this time, participants will have 3 visits at the study clinic.
Substudy B will investigate 2 formulations of RSVpreF + qIRV of different volumes and osmolaities (concentrations). These formulations will be examined for safety, tolerability, and immunogenicity, with the goal of selecting a formulation for further study.
This study is seeking participants who:
* are 50 years or older
* are healthy or have well-controlled chronic conditions
* have not had a flu shot in the last 180 days
* and agree to be present for all study visits, procedures, and blood draws.
The participants will be divided into 2 groups. Group 1 will receive RSVpreF plus qIRV in a 1.0-mL formulation while Group 2 will receive RSVpreF plus qIRV in a 0.5-mL formulation.
The investigators will examine the experiences of the participants receiving the study vaccines. This will help the investigators determine if the study vaccines are safe, well tolerated and produce a similar immune response.
Participants will be involved in this study for 1 month. During this time, participants will have 2 visits at the study clinic.