This clinical trial is being done to learn more about how well a vaccine (Arexvy®) for respiratory syncytial virus, also known as RSV, works in people with weakened immune systems. The main questions it aims to answer are: * Does 1 or 2 doses of Arexvy work better in people with weakened immune systems? * What medical problems do participants have after receiving Arexvy? Participants with weakened immune systems will: * Receive 3 study vaccines over the course of 1 year * Keep a diary of symptoms for 7 days after each vaccine * Have 3 in-person follow up study visits for checkups and tests over the course of 1.5 years * Have 6 phone follow up study visits over the course of 1.5 years
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Geometric Mean Titer (GMT) (ED60 RSV A and B)
Timeframe: At 30 days post 1st and 2nd dose in Arm 1 and Arm 2
Immune response elicited by adjuvanted RSVPreF3 (Arexvy) in immunocompromised adults as determined by titers of neutralizing antibody ED60 against RSV A and B
Timeframe: At 30 days post 2nd dose (Arm 2) and 30 days post 1st dose (Arm 1)