Question

A mother brings her 7-month-old female infant to the pediatrician's office in early November for a routine well-child evaluation. The infant was born prematurely at 28 weeks of gestation. Her neonatal course was complicated by respiratory distress syndrome, requiring mechanical ventilation and exogenous surfactant administration. She was successfully extubated and eventually discharged home at 36 weeks corrected gestational age without the need for supplemental oxygen. The mother reports that the infant is feeding well, gaining weight, and has not been hospitalized since birth. Vital signs are temperature 37.1°C (98.8°F), heart rate 120/min, and respiratory rate 30/min. Physical examination reveals a healthy-appearing infant with clear breath sounds bilaterally and no cardiac murmurs. The mother expresses concern about the upcoming winter season and asks what can be done to protect her child's lungs from severe viral infections. Assuming all routine immunizations for her age are up to date, which of the following is the most appropriate additional pharmacological intervention for this patient?