Effect of the Coronavirus Disease 2019 Pandemic on Age-Specific Coinfections of Respiratory Viruses

Background: The coronavirus disease 2019 (COVID-19) pandemic altered the epidemiology of pediatric respiratory infections.Non-pharmaceutical interventions (NPIs), such as school closures and mask mandates, effectively suppressed viral transmission but reduced exposure to common respiratory pathogens, leading to "immune debt."This study investigated long-term changes in respiratory virus detection rates and coinfection patterns before and after the pandemic.Methods: Multiplex reverse transcriptase polymerase chain reaction (mRT-PCR) and COVID-19 real-time RT-PCR results from nasopharyngeal swabs collected at a single tertiary-care hospital between 2013 and 2023 were retrospectively analyzed.Coinfections were evaluated using the Jaccard similarity coefficient (JSC), and age-and period-specific coinfection networks were constructed.Results: Among 128,148 tests, positivity rates were 6.5% for COVID-19 and 55.2% for other respiratory viruses.The most frequently detected viruses were rhinovirus, adenovirus, enterovirus, and bocavirus.Before the pandemic, bocavirus served as the central hub in coinfection networks.During the pandemic, enveloped viruses such as respiratory syncytial virus (RSV) and influenza A/B markedly declined, whereas non-enveloped viruses, including rhinovirus and adenovirus, remained prevalent.After NPI relaxation in 2023, positivity rates of rhinovirus, enterovirus, bocavirus, parainfluenza virus 3 (PIV3), and RSV A increased notably in children under 7 years.JSC analysis revealed denser and stronger coinfection networks centered on rhinovirus-enterovirus-bocavirus-PIV3 interactions, particularly in younger age groups.Conclusions: The post-COVID-19 resurgence of multiple viral coinfections among young children likely reflects increased susceptibility associated with immune debt.These findings provide baseline data for pediatric respiratory infection surveillance and for interpreting multiplex diagnostic results.