This study is for adults 60+ who were part of a previous RSV vaccine study. RSV, or Respiratory Syncytial Virus, can cause lung infections. The new study aims to learn the best time to give booster shots and check how long the immune protection lasts. People who only got a placebo, which is a harmless substance, in the earlier study now have a chance to get the real vaccine. The study will last for about 60 months, or 5 years, and participants need to stay in touch through phone calls and visits. You can join if you’re medically stable, even with conditions like diabetes or heart disease. However, if you have a weak immune system or serious health issues, you can’t participate. The study excludes those with a history of severe allergic reactions or certain other medical problems. Participants can't take part if they are involved in another clinical study or have received other vaccines not allowed by the study.

• Study lasts about 5 years with regular check-ins.
• Participants must be stable health-wise.
• Some medical conditions can prevent participation.