Q. A 9-month-old infant is brought to the pediatrician's office by her concerned parents. They report that the baby has been coughing and wheezing for the past few days, along with mild fever and nasal congestion. The infant was born at 28 weeks of gestation and has a history of chronic lung disease. The family reports that their other child, a 3-year-old, recently had a respiratory infection. The infant's vital signs are as follows: temperature 100.2°F (37.9°C), heart rate 140 bpm, respiratory rate 48 breaths/min, and oxygen saturation 93% on room air. The physical examination reveals nasal flaring, retractions, and bilateral crackles on lung auscultation. The pediatrician suspects that the infant might have a respiratory syncytial virus (RSV) infection. What would have been the most appropriate prophylactic intervention for this infant's condition?