Comparison of clinical characteristics of hospitalized pediatric patients with respiratory syncytial virus infections before and during/after the coronavirus disease 2019 pandemic in Japan -importance of universal prevention using maternal vaccination and nirsevimab.

Background: The coronavirus disease 2019 (COVID-19) pandemic has impacted the epidemiology of respiratory syncytial virus (RSV) infections. In this study, we aimed to elucidate the impact of COVID-19 on the clinical characteristics of hospitalized RSV-infected pediatric patients in Japan and to discuss the potential future roles of the maternal RSV prefusion F protein-based vaccine (RSVpreF) vaccine and universal nirsevimab in Japan.

Methods: This retrospective study investigated RSV-infected pediatric patients hospitalized at Niigata City General Hospital, Niigata, Japan, from 2017 to 2023. We extracted the clinical characteristics of patients from their electronic medical records.

Results: A total of 407 RSV-infected patients were hospitalized: 210 (51.6 %) were hospitalized before the pandemic, and 197 (48.4 %) were hospitalized during/after the pandemic. Age distribution and patients' backgrounds between the two periods did not differ significantly (p > 0.16). However, the proportion of patients who required intensive care unit (ICU) admission increased from 6.7 % (14/210) to 18.8 % (37/197), with increased ICU admission rates observed especially in those aged 1-2 months (5.4 % vs. 23.7 %, p = 0.006). Moreover, 188 (46.2 %) hospitalized patients were neonates and infants less than 6 months old without a risk of severe RSV disease, of which 33 were admitted to the ICU throughout the study period.

Conclusions: More patients with severe RSV infection were hospitalized during/after the COVID-19 pandemic in Japan than before the COVID-19 pandemic. To prevent RSV infection in such populations, wider distribution of the maternal RSVpreF vaccine or universal use of nirsevimab is warranted.