Incidence of Severe Respiratory Syncytial Virus Infections in Preterm Brazilian Children

Inclusion Criteria: * Male and female infants that were born \<35 weeks gestational age * The inclusion must be done during the following period: * 24 hours prior confirmed maternity hospital discharge date, or * Up to 72 hours after documented maternity hospital discharge date. In this case, RSV rapid test must be performed and subjects should be enrolled only if the results is negative. * Less than 6 months of age at screening * Born into or transferred to a participating hospital * Able to receive follow-up medical care at the participating site and provide information during the follow-up period * The legal representative is capable of understanding and complying with parameters as outlined in the protocol and able and willing to participate in this study, by signing the informed consent approved by an Independent Ethics Committee (IEC)/Institutional Review Board (IRB), after all the aspects of the study that might be relevant for his/her decision to participate are explained and all his/her questions and doubts are elucidated, and prior to the initiation of any screening or study-specific procedures. Exclusion Criteria: * RSV infection prior inclusion. * Receipt of palivizumab or other immunoglobulin preparation containing RSV specific antibodies (i.e. RSV hyperimmunoglobulin, polyclonal intravenous immunoglobulin, cytomegalovirus hyperimmunoglobulin, varicella-zoster hyperimmunoglobulin)