BackgroundPreterm infants born between 33 and 35 weeks of gestational age (wGA) have been considered a “major underserved population” and ineligible to receive palivizumab (PLV), the only drug authorized to date for respiratory syncytial virus (RSV) prophylaxis, by current international guidelines. In Italy, such a vulnerable population is currently eligible for prophylaxis, and, in our region, specific risk factors are taken into consideration (SINLazioscore) to target prophylaxis for those at highest risk. Whether the adoption of less or more restrictive eligibility criteria for PLV prophylaxis would translate into differences in bronchiolitis and hospitalization incidence is not known.Materials and methodsA retrospective analysis was conducted in 296 moderate-to-late preterm infants (born between 33 and 35+6weeks) who were being considered for prophylaxis in two epidemic seasons: 2018–2019 and 2019–2020. The study participants were categorized according to both the SINLazioscore and the Blanken risk scoring tool (BRST), which was found to reliably predict RSV-associated hospitalization in preterm infants on the basis of three risk factor variables.ResultsBased on the SINLazioscore, approximately 40% of infants (123/296) would meet the criteria to be eligible for PLV prophylaxis. In contrast, none of the analyzed infants would be considered eligible for RSV prophylaxis on the basis of the BRST. A total of 45 (15.2%) bronchiolitis diagnoses were recorded on average at 5 months of age in the overall population. Almost seven out of 10 (84/123) patients exhibiting ≥3 risk factors to be eligible for RSV prophylaxis according to SINLaziocriteria would not be receiving PLV if they were categorized on the basis of the BRST. Bronchiolitis occurrence in patients with a SINLazioscore ≥3 was approximately 2.2 times more likely than that in patients with a SINLazioscore <3. PLV prophylaxis has been associated with a 91% lower risk of requiring a nasal cannula.ConclusionOur work further supports the need for targeting late preterm infants for RSV prophylaxis and calls for an appraisal of the current eligibility criteria for PLV treatment. Therefore, adopting less restrictive criteria may ensure a comprehensive prophylaxis of the eligible subjects, thus sparing them from avoidable short- and long-term consequences of RSV infection.