Clinical and epidemiological changes in severe viral respiratory infections in pediatric patients after the COVID-19 pandemic in Spain

The COVID-19 pandemic and associated public health measures disrupted the circulation of respiratory viruses worldwide. However, the long-term impact of these changes on pediatric respiratory tract infections (ARTIs) remains incompletely understood. We conducted a prospective study in children under 14 years hospitalized for ARTIs in Severo Ochoa Hospital (Spain) from January/2006 to September/2023. The cohort was divided into three periods: pre-pandemic (T1), pandemic (T2), and post-pandemic (T3). Clinical and virological results were compared. 6048 children were included (T1:5,101; T2:122; T3:825). Viral detection increased in T3 (91%) compared to T1 (78.7%) and T2 (69.5%), p < 0.001, with higher rate of coinfections, p < 0.001, and pneumonia diagnoses, p < 0.001. HRV and RSV were the most frequent viruses across periods, with HRV maintaining year-round circulation and RSV showing marked seasonal disruption in T2, followed by return to its typical winter pattern in T3. Detection of PIV and HMPV increased in T3, with altered seasonal peaks and a shift toward older age groups. Influenza infections, nearly absent in T2, re-emerged in T3 with delayed seasonal peaks and higher median ages. HBoV circulation declined and became more evenly distributed throughout the year. Clinically, children in T3 were older, with more hypoxia, radiological infiltrates, and pneumonia, while bronchiolitis cases decreased. Most pneumonia cases in T3 had a viral etiology, with HRV, RSV, HMPV, and PIV as the main contributors. Post-pandemic shifts in viral circulation and disease profiles among children with ARTIs highlight the ongoing impact of COVID-19 on pediatric respiratory health. The increased burden of viral pneumonia and the change in seasonal distribution of infections underscore the need for updated surveillance, diagnostic strategies, and prevention programs tailored to the post-pandemic context.