Observational Program to Assess Respiratory Syncytial Virus (RSV) Hospitalization Rate in Population of Children at High-risk of Serious RSV Illness Who Received Palivizumab Immunoprophylaxis

* Planned prescription of palivizumab for immunoprophylaxis during RSV season or participants for whom palivizumab was prescribed and who received the first dose of palivizumab no later than 60 days before enrollment in the study * Infants at high risk of severe RSV infection defined as fulfilling at least one of the following: * Infants born ≤35 weeks gestational age AND are ≤6 months of age at the onset of the RSV season; * Infants ≤24 months of age AND with a diagnosis of BPD (defined as oxygen requirement at a corrected gestational age of 36 weeks); * Infants ≤24 months of age with hemodynamically significant CHD, unoperated or partially corrected. * Written authorization to use individual data signed by parents or child representative

* Major congenital malformation aside from CHD * Chronic pulmonary disease other than BPD * Acute period of any infection * Contraindication to palivizumab prescription according to local label * Administration of a product possibly containing RSV-neutralizing antibody within 30 days prior to enrollment or current administration (includes, but is not restricted to, the following: RSV hyperimmunoglobulin, polyclonal intravenous immunoglobulin, cytomegalovirus hyperimmunoglobulin, varicella zoster hyperimmunoglobulin)