Respiratory syncytial virus affects 64 million people worldwide every year, hospitalizing 3 million children under 5 years old and costing US$5.45 billion globally. A vaccine or treatment would drastically reduce hospital and intensive-care admissions for infants under two months old, who are most vulnerable. Now, following a key discovery in 2013, an effective RSV vaccine is nearly within reach: four candidates and one monoclonal antibody treatment are in late-stage clinical trials. Once approved, an RSV vaccine will be most useful for the very young and the very old. But to simplify trials, all four companies are initially testing their shots in people older than 60.