This study looks at two experimental vaccines aimed at protecting against viruses named RSV (Respiratory Syncytial Virus) and hMPV (Human Metapneumovirus). The focus is to see if these vaccines are safe and how the body responds to them in adults, both young (18-49 years old) and older (60-80 years old). To join, you must agree to follow the study’s rules, be in good health, and have a Body Mass Index (BMI) between 18 and 33.

• Study involves follow-up visits and using an electronic diary (eDiary).
• Participants must not have certain health conditions or allergies.
• No participation if using certain medications or other vaccines recently.

Before joining, you will need to give written permission and agree to the study's requirements. If you're a woman who can have children, you'll need to use two types of birth control during the study. This study will help researchers learn more about these vaccines' safety and effectiveness. Participation in any other clinical study during this period is not allowed.