Respiratory Syncytial Virus (RSV), a member of the Paramyxoviridae family, is the leading cause of lower respiratory tract illness (LRI) in infants. From 1993 to 2008, the total RSV hospitalization rate in the United States across all age groups was 55 per 100,000 person-years, slightly lower than the rate of 64 per 100,000 personyears for influenza viruses [1]. In infants, the hospitalization rate was 2,345 per 100,000 person-years for RSV compared to 151 for influenza, consistent with reports that RSV hospitalizes 1–2% of infants in the US each winter, a staggering statistic [1]. RSV disease is not limited to infants. RSV resulted in more hospitalizations in 1–4-year-olds than influenza [1]. One in 13 children under the age of five in the US required medical attention for RSV each year, and 60% of office visits were for 2–5-year-olds [2]. RSV remains a significant cause of death. Over all age groups, influenza caused three times as many deaths as RSV in the US from 1990 to 1999, mostly in the elderly [3]. RSV caused 137 deaths per year in the US in children less than 4 years old, compared to 38 per year in this age group for influenza [3]. Globally, RSV was estimated to have caused 66,000 to 199,000 pneumonia deaths in children less than 5 years old in 2005, making RSV the third most important cause of deadly childhood pneumonia after Streptococcus pneumonia and Haemophilus influenza [4]. RSV is increasingly recognized as a global health priority. Other than ribavirin, there are no licensed RSV vaccines or therapeutics. The monoclonal antibody (mAb) palivizumab is a neutralizing mAb against a conserved epitope in the viral fusion (F) surface glycoprotein. Palivizumab is administered prophylactically to high-risk infants, such as those with chronic lung disease of prematurity, congenital heart disease, or premature birth at less than 36 weeks gestational age, but it costs $4,500 per patient treatment course [5].