Safety of timely immunization with nirsevimab in hospitalized preterm infants.

We aimed to assess the safety profile of nirsevimab in hospitalized preterm infants (PT). We conducted an observational, uncontrolled, prospective study in clinically stable PT admitted to the neonatal unit. One hundred and ten PT were eligible for immunization; uptake was 93.5 % (n = 103) (median GA and BW of 33 weeks and 1892 g, respectively), and a median age at immunization of 3 days. No anaphylaxis, seizures or local AE were reported. 16.5 % (n = 16) reported systemic AEs. Fever (n = 8) was mild (median of 38 °C). 8.7 % (n = 9) experienced apneas (median of 26 h post-immunization), mainly in PT with lower GA. Eight recovered with tactile stimulation, and one required intubation which was unrelated to nirsevimab injection. Bradycardia occurred only in two PT during apneic episodes, being both fully recovered with tactile stimulation. Nirsevimab administration was safe regardless GA or BW, with apnea reported mainly in those <32 weeks. Therefore, we recommend early and monitored administration of nirsevimab in hospitalized PT during RSV season.