Changes in the Seasonality of Bronchiolitis Caused by Respiratory Syncytial Virus During and After the COVID-19 Pandemic.

Background: Prior to the coronavirus disease 2019 (COVID-19) pandemic, bronchiolitis caused by respiratory syncytial virus (RSV) was primarily observed during the winter months. Recently, however, an increase in incidence during the warmer months has been noted. This trend suggests an interaction between RSV and coronavirus, as well as the impact of public health measures, such as hand hygiene, mask-wearing, and social distancing.

Objectives: To characterize bronchiolitis cases in children under 2 years old caused by RSV during the COVID-19 pandemic in Israel from 2018 to 2022.

Methods: We conducted retrospective study by analyzing medical records of children hospitalized with bronchiolitis from January 2018 to December 2022. A comparison was made between cases before and after the first COVID-19 lockdown.

Results: A total of 922 children with bronchiolitis were studied: 276 cases occurred before the lockdown and 646 cases afterward. We found an increase in bronchiolitis frequency during the summer following the lockdown and a decrease during the winter (P < 0.0001). In addition, there was a shift in the pathogenic profile, with a notable rise in mixed infections after the lockdown (P < 0.0001). No significant differences in clinical presentation were observed between pre- and post-lockdown periods.

Conclusions: There was a change in bronchiolitis seasonality after the lockdown, with a significant increase in cases during the summer and a rise in mixed infections. Further studies are needed to assess whether this shift is a lasting consequence of the pandemic or a temporary change.