INTRODUCTION
Respiratory syncytial virus (RSV) is a leading cause of lower respiratory tract (LRTI) globally and the second leading pathogen to cause infant mortality.1,2 Most deaths occur in low- and middle-income countries.1,3 In the United States, an estimated 58 000–80 000 young children are hospitalized annually with RSV, with the highest incidence in infants aged less than 6 months,4,5 most of whom are healthy. RSV prevention has been long recognized as a priority to improve children’s health; however, the path to achieve this has been defined by both significant breakthroughs and setbacks.4