Distinct seasonality and increased respiratory failure in RSV patients < 2 years of age after emergence of SARS-CoV-2: data from the multicentric, prospective PAPI study.

Respiratory syncytial virus (RSV) is a leading cause for global infant morbidity and mortality. The COVID-19 pandemic caused significant shifts in seasonality of RSV, and changes in disease severity have been matter of intense discussion. Between September 2020 and February 2023, the multicentric, prospective PAPI study analyzed rates and phenotypes of hospitalized RSV patients aged ≤ 24 months across three German hospitals. Pseudonymized patient data were analyzed employing Mann-Whitney U and chi-square testing, or one-way ANOVA or Kruskal-Wallis testing when more than two groups were compared. Additionally, RSV cases from seasons 2017/2018-2020/2021 were retrospectively analyzed. After its absence in 2020/2021, RSV returned approximately 2 months earlier than usual in late 2021. Overall duration of the season and patient numbers were comparable to previous seasons, and no significant shifts in age and gender distributions occurred in our cohort. While duration of hospitalization did not differ between the periods before vs. after the emergence of SARS-CoV-2, a significantly higher rate of patients with hypoxemia and respiratory failure occurred after the onset of the pandemic (oxygen supplementation post vs. pre: 59.4% vs. 54.8%, p < 0.001, non-invasive ventilation post vs. pre: 12.4% vs. 7.2%; p < 0.001). No deaths occurred during the entire observational period.

Conclusion: We present comprehensive data on distinct seasonality and increased disease severity in children hospitalized with RSV bronchiolitis before and after the onset of the SARS-CoV-2 pandemic. Our data aids in understanding the impact of the pandemic on RSV disease in infants and provides valuable information on the impact of RSV on pediatric healthcare prior to broad introduction of novel prevention measures such as nirsevimab.

What is known: • Respiratory syncytial virus (RSV) is a leading cause of infant morbidity and mortality globally. • COVID-19 has led to significant shifts in RSV seasonality, and concerns about shifts in RSV severity.

What is new: • This study shows distinct seasonality and significant shifts in diseases severity amongst children with RSV associated hospitalization under the age of 2 yrs in the last years in Germany. • It reports significantly higher rates of RSV associated respiratory failures in children < 2 yrs. of age after emergence of the pandemic.