Additional Study Information: The main purpose of this research project is to study a vaccine made to prevent disease due to infection with the Respiratory Syncytial Virus (RSV). We want to find out how the body responds to the RSV vaccine, as well as look at the safety of the vaccine. RSV is a common virus that can cause infections of the air passages. Adults 60 years of age and older have a higher risk of getting severe RSV disease than younger adults. However, adults below 60 years of age with long-term (chronic) health conditions may also have a higher risk of severe RSV disease. These health conditions may include long-lasting lung and heart diseases, diabetes, liver, and kidney diseases, as well as a weaker immune system due to disease or medication. Even though the symptoms can be similar, RSV infections and influenza (flu) are caused by different viruses. Therefore, you can still get an RSV infection even if you have been vaccinated against the flu. This study will be done in adults 18 years and older, and consists of two different groups: adults 50 years of age and above who are healthy or medically stable (Participants with chronic stable medical conditions with or without specific treatment, such as diabetes, high blood pressure, or heart disease, are allowed to participate in this study if considered by the study doctor as medically stable), and adults 18 years of age or above, who underwent a kidney or lung transplant at least 1 year before taking part in this study, and who are at higher risk of getting severe RSV. It is important to understand this study vaccine has not yet been approved by the Food and Drug Administration FDA to be used in these populations.