Severity of respiratory syncytial virus through the COVID-19 pandemic among infants aged ≤2 months: a secondary analysis of the IRIDE cohort study

Background: Through the SARS-CoV-2 pandemic the severity of RSV infection increased among children, but little is known about its evolution among infants ≤60 days of life (DOL). Methods: Multicenter observational retrospective study conducted in 27 hospitals in Lombardy, Italy, comparing outcomes of infants (≤60 DOL) hospitalized with RSV bronchiolitis during 4 seasons: 2018-2019 (pre-pandemic period), 2020-2023 (pandemic seasons). Result: 1816 infants were included. Multivariable regressions showed that the need and length of O2-supplementation were significantly higher in pandemic seasons compared to the pre-pandemic one, as the need for non-invasive ventilation. Among neonates (≤28 DOL), no difference was observed between pre- and pandemic seasons besides an increased length of O2-supplementation. Conclusion: Outcomes of RSV bronchiolitis among infants ≤60 DOL were slightly affected by COVID-19 pandemic. The impact was less significant among neonates. Breast milk components might have mitigated the negative effect of COVID-19 on RSV severity in neonates. Category of study: Clinical and population study. Impact: Outcomes of RSV bronchiolitis among infants ≤60 days of life (DOL) were slightly affected by COVID-19 pandemic. Neonates (≤28 DOL) in our cohort seem to have significantly better outcomes than older infants (29-60 DOL). To date no data is available on the effects of non-pharmacological interventions on the diffusivity and severity of RSV infection in infants aged ≤60 DOL, the population at highest risk for RSV-related complications Breast milk and its innate immune components may have played an important role as protective factors against RSV respiratory infections during the first month of life.