BackgroundPrematurity and infection with respiratory syncytial virus (RSV) are major risk factors for impaired lung function beyond the neonatal period. Research QuestionTo examine the long-term effects of palivizumab immunoprophylaxis in the first year of life on lung function and frequency of bronchitis episodes in 5 to 6-year-old preterm infants. Study Design and MethodsPreterm infants with a birth weight below 1500 grams (Very low birth weight infants, VLBWI) were enrolled in a German Neonatal Network (GNN) cohort study between 2009 and 2016. Children were examined by a single follow-up team at 5 to 6 years of age. VLBWI who received at least five doses of palivizumab were compared with children who never received palivizumab. Analyses were stratified by bronchopulmonary dysplasia (BPD) and gestational age. We analysed forced vital capacity (FVC), forced expiratory volume in one second (FEV1), FEV1/FVC, and the risk for respiratory tract infections at the age of 5 to 6 years via univariate analyses and linear and logistic regression models. ResultsOut of N = 1986 VLBWI with follow-up at 5-6 years, N = 951 (48%) received immunoprophylaxis with palivizumab. Children with BPD (N = 1019) had a much lower FEV1 than children without BPD (median FEV1 z-score -1.51 vs. -1.09; p< 0.001). However, FEV1 in children with BPD was not altered by palivizumab (median FEV1 z-score in 698 children with BPD and palivizumab: -1.57; IQR -0.75 to -2.43 vs. 320 children with BPD without palivizumab: -1.37; IQR -0.69 to -2.25; p= 0.1). As for FEV1, we did not find any protective effects of palivizumab for other endpoints or in other risk groups. InterpretationPalivizumab immunoprophylaxis in VLBWI is not associated with improved lung function or lower rates of respiratory tract infections in early school-age infants.