Hospitalisations for respiratory tract infections in preterm and term born children aged 1-5 years before, during and after COVID-19 control measures: an interrupted time-series analysis.

BACKGROUND: Preterm-born children are vulnerable to respiratory tract infections (RTIs), but we know little about how these were affected by COVID-19 pandemic control measures. METHODS: We studied Norwegian population-wide registry data on 1-5-year olds born 2012-2021. RTI hospitalisations were identified from primary hospitalisation diagnosis codes. We modelled prepandemic hospitalisation rates, January 2017 to March 2020, using quasi-Poisson regression with harmonic seasonal terms. These were compared with monthly hospitalisation rates, March 2020 to December 2022. The calculations were performed separately for gestational age groups: 23-33, 34-36, 37-41 completed weeks. RESULTS: We identified 9734 RTI hospitalisations among 449 105 children aged 1-5 years, with higher rates in the most preterm groups. Across gestational ages, we observed lower hospitalisation rates during control measures in 2020, followed by a surge after measures were lifted in 2021. For children born in weeks 23-33, the rate reduction with 95% CI during the first year of the pandemic compared with the prepandemic years was -21 per 1000 person-years (95% CI -30 to -13), whereas in April-December 2022, there was an increase of 22 (95% CI 12 to 31). For term born (week 37-41), the corresponding changes were -4.9 (95% CI -5.5 to -4.3) and 3.6 (95% CI 2.9 to 4.2). CONCLUSIONS: Compared with term born, preterm-born children of all gestational age groups were more distinctly protected by pandemic control measures. They were also more affected by the resurgence of infections when measures were lifted. These findings call for policies to protect preterm-born children better from RTIs, especially when viral spread is high.