Are late preterm infants as susceptible to RSV infection as full term infants?

Preterm infants are at increased risk of being rehospitalised during the first few months of life with severe respiratory syncytial virus (RSV) lower respiratory tract infection (LRTI) that usually manifests as apnea and hypoxemia. This occurs more commonly in preterm infants < 33 weeks gestational age (GA), but recent studies demonstrate that late preterm infants (those born between 34 weeks and 0 days to 36 weeks and 6 days GA) are equally susceptible to RSV LRTI as those with lower GA. Factors associated with severe LRTI include immaturity of both the humoral and cell-mediated immune system and interrupted lung development prior to 36 weeks GA which results in lower functional residual capacity, reduced compliance, diminished forced expiratory air flow and impaired gas exchange. Morbidity and mortality are significantly increased in late preterms compared to their term counterparts. Prophylaxis with palivizumab against RSV infection seems to be crucial. Due to the large number of infants in this age group, additional risk factors have been identified in order to tailor palivizumab prophylaxis effectively to those at highest risk for severe RSV LRTI.