Surge of Pediatric Respiratory Tract Infections after the COVID-19 Pandemic and the Concept of Immune Debt

Objective: To investigate a dose-response relationship between the magnitude of decrease in pediatric respiratory tract infections (RTIs) during the 2020 implementation of nonpharmaceutical interventions (NPIs) and the increase thereafter during NPI lifting. Study design: We conducted an interrupted, time-series analysis based on a multinational surveillance system. All patients <16 years of age coming to medical attention with various symptoms and signs of RTI at 25 pediatric emergency departments from 13 European countries between January 2018 and June 2022 were included. We used generalized additive models to correlate the magnitude of decrease of each RTI during NPI (such as social distancing) implementation and its subsequent increase during NPI lifting. Urinary tract infections served as control outcome. Results: In total, 528 055 patients were included. We observed reductions in cases during the NPI period, from −76% (95% CI −113 to −53 in pneumonia) to −65% (95% CI −100 to −39 for tonsillitis/pharyngitis), followed by strong increases during NPI lifting, from +83% (95% CI 29-150 for tonsillitis/pharyngitis) to +329% (95% CI 149-517 for bronchiolitis). For each RTI, we found a significant association between the magnitude of decrease during NPI implementation and the increase during NPI lifting. Urinary tract infection cases remained stable. Conclusions: The magnitude of increase in RTI observed after NPI lifting was directly correlated to the magnitude of case reduction during NPI implementation, suggesting a “dose-response” relationship from an “immune debt” phenomenon. The likely rebound in RTIs should be expected when implementing and lifting NPI in the future.