Burden of disease and seasonal data of children hospitalized due to RSV and Influenza infection before, during and after the COVID-19 pandemic.

We sought to assess the burden of disease of RSV and influenza in hospitalized children in the context of the COVID-19 pandemic and its preventive measures in the winter seasons from 2019/2020 to 2023/2024. We compared both diseases by means of a retrospective, single-center study from October 1, 2019, to April 30, 2024, including infants and children up to 18 years hospitalized due to an RSV and/or influenza infection at Clinic Donaustadt, Vienna. Infection had to be proven by polymerase chain reaction or antigen test. By evaluating each single hospital course, we analysed seasonality, detailed patient characteristics and parameters of disease severity. Overall, there were 894 children hospitalized, 561 due to RSV and 314 due to influenza, 19 due to both viruses. Cases with RSV infection were younger of age (mean: 16.5 vs. 58.1 months; p < 0.05) and had longer hospital stays (mean: 7 vs. 4.5 days; p < 0.05). A respiratory severity index was higher in children with RSV infection. Mortality was low (0.3% RSV, 0.6% Influenza). Seasonality changed remarkably before, during and after the pandemic. Disease severity did not change substantially in both diseases. Respiratory support was used more frequently post-pandemic (18.9% vs. 39.9%; p < 0.05).

conclusionCOVID-19 pandemic and its prevention measures were associated with significant changes in RSV and influenza virus seasonality but did not influence the severity of both diseases. The last season 2023/24 showed a tendency to a return to a pre-pandemic pattern. WHAT IS KNOWN: • The COVID-19 pandemic and its prevention measures changed the seasonal pattern of RSV and Influenza. If the immunity gap also led to more severe courses of diseases remained uncertain so far. WHAT IS NEW: • The stable setting of a single center through five seasons offered the opportunity to determine the impact of the pandemic and in-depth analysis of hospital courses. • The study finds no substantial augmentation of severity in hospitalized infants and children.