This clinical trial is focused on studying the prevention of Respiratory Syncytial Virus (RSV) in healthy infants. RSV is a common virus that can cause infections in the lungs and respiratory tract, particularly in young children. The study will test a treatment called MK-1654, developed by Merck & Co. Inc., to see how safe it is and how well it works in preventing RSV-related respiratory infections in infants. The trial will compare MK-1654 to a placebo to evaluate its effectiveness and safety.

The purpose of the study is to assess how well MK-1654 can prevent RSV-associated medically attended lower respiratory infections in both pre-term and full-term infants. The study will involve monitoring the infants from the time they receive the treatment up to 150 days afterward. During this period, researchers will observe the infants for any signs of RSV-related infections and any side effects that may occur.

Participants in the study will include healthy infants who are either early or moderate pre-term (born between 29 to 34 weeks and 6 days of gestational age) or late pre-term or full-term (born at 35 weeks or later). The study will also track any adverse events, such as fever or rash, to ensure the safety of the treatment. The ultimate goal is to determine if MK-1654 can effectively reduce the incidence of RSV-related infections in infants, providing a potential new option for preventing this common and sometimes serious virus.