Gerard Notario,1 Pamela Vo,2 Katherine Gooch,2 Roger Deaton,3 Xionghua Wu,4 Brian Harris,4 Parthiv J Mahadevia,4 Pablo J Sánchez51Clinical Development and Medical Affairs, 2Global Heath Economics and Outcomes Research, 3Statistics, AbbVie Inc., North Chicago, IL, 4MedImmune, LLC, Gaithersburg, MD, 5The Research Institute at Nationwide Children's Hospital, The Ohio State University, Columbus, OH, USABackground: Respiratory syncytial virus (RSV) infections are common during childhood and are a major cause of hospitalization resulting from serious lower respiratory tract infections. Palivizumab is approved for prevention of serious lower respiratory tract disease caused by RSV infection in infants and young children at high risk of RSV disease. Although the previously published IMpact-RSV trial included the overall results for palivizumab prophylaxis in a cohort of premature infants who did not have bronchopulmonary dysplasia (BPD), there is an ongoing demand to understand the efficacy of palivizumab in premature infants without BPD by gestational age group.Methods: This post hoc analysis assesses IMpact-RSV trial data within eleven gestational age groups for the cohort of 724 premature infants who were ≤6 months of age and did not have BPD. RSV-related hospitalization rates along with corresponding 95% exact binomial confidence intervals were determined for these specific gestational age groups. Relative reductions in risk of RSV-related hospitalizations for palivizumab versus placebo with corresponding 95% confidence intervals were also calculated.Results: Analysis of a cohort of premature infants without BPD from the IMpact-RSV trial revealed that palivizumab consistently reduced RSV-related hospitalizations (64.5%–100%) versus placebo in all eleven gestational age groups evaluated. Palivizumab significantly decreased the relative risk of RSV-related hospitalization (73%–82%, P<0.05) versus placebo in the 28–31, 29–32, 29–33, 32–34, and 32–35 gestational week age groups. Relative reductions in risk for RSV-related hospitalizations were substantial for the moderate/late preterm groups (82% for both the 32–34 and 32–35 gestational week age groups).Conclusion: Palivizumab effectively reduced RSV-related hospitalization rates in premature infants without BPD across all gestational age groups evaluated. In particular, reductions in RSV-related hospitalizations were substantial for the moderate/late preterm groups (32–34 and 32–35 gestational weeks).Keywords: respiratory syncytial virus, bronchopulmonary dysplasia, palivizumab, gestational age, prophylaxis