Natural Polymorphisms and Resistance-Associated Mutations in the Fusion Protein of Respiratory Syncytial Virus (RSV): Effects on

Specific mutations in respiratory syncytial virus (RSV) fusion protein can cause palivizumab resistance. We assessed the in-cidence of sequence polymorphisms andpalivizumab resistance in clinical RSV isolates collected from immunoprophylaxis-naive subjects. Polymorphismswere identified at low frequency, and only polymorphicmutations in antigenic site A (,1%of all polymorphisms) conferred palivizumab resistance. Respiratory syncytial virus (RSV) is an important pathogen that causes annual worldwide epidemics of bronchiolitis and pneu-monia in infants and young children [1, 2]. The hospitalization rate for RSV disease in infants with a history of premature birth or congenital heart disease is higher than the general infant population [3, 4]. Palivizumab, an RSV-specific humanized monoclonal antibody (mAb), has been approved for use in the United States since 1998 [5]. Palivizumab binds antigenic site A