Epidemiological Changes in Respiratory Viral Infections in Children: The Influence of the COVID-19 Pandemic.

Background: Viruses are the major cause of acute respiratory infections in children, causing important morbimortality. Before the COVID-19 pandemic, in temperate regions, respiratory viruses displayed a typical seasonality in transmission. A disruption in this pattern was observed in several countries during the pandemic, with low prevalence during the typical season, and an interseasonal rise. We evaluated the effects of the COVID-19 pandemic in the epidemiology of non-COVID viral respiratory infections in children, in a tertiary care hospital in Portugal.

Methods: Between March 2020 and August 2022, nasopharyngeal samples from children with respiratory symptoms in the Emergency Department (ED) and the Pediatric Ward were tested for RSV, influenza and other respiratory viruses, by real-time reverse transcriptase PCR (RT-PCR).

Results: A seasonal variation was observed from 2018 to 2020, with prevalence increasing in winter (mainly RSV and influenza). In the winter of 2020/21, when measures to mitigate SARS-CoV-2 transmission were stricter, there was a disruption of the seasonal pattern, with unusually low numbers. In the summer of 2021, when measures were being relaxed, there was an atypical rise. In June 2021, RSV was first detected and peaked in October. Influenza (Influenza A H3) was detected for the first time in February 2022, peaking in March/April.

Conclusions: These findings show a disruption of the seasonality of viral respiratory infections in children during the pandemic, with a virtual elimination during the months of usually higher prevalence, and a subsequent out-of-season increase, coinciding with variations in the measures implemented to control the SARS-CoV-2 transmission, and confirming their efficacy.