Background: Social distancing measures are used to reduce the spreading of infection. Our aim was to assess the immediate effects of national lockdown orders due to coronavirus disease 2019 (COVID-19) on pediatric emergency room (ER) visits and respiratory tract infections in hospitals and nationwide in Finland. Methods: This register-based study used hospital patient information systems and the Finnish national infectious disease register. The participants were all patients visiting pediatric ER in 2 Finnish hospitals (Kuopio University Hospital, Mikkeli Central Hospital) covering 1/5th of the Finnish children population, 4 weeks before and 4 weeks after the start of the nationwide lockdown on March 16, 2020. Nationwide weekly numbers of influenza (A + B) and respiratory syncytial virus (RSV) in children were assessed from the infectious disease register from 2015 to 2020. Results: A major decrease in the rate of daily median pediatric ER visits was detected in both hospitals in the study during the nationwide lockdown compared with the study period before the lockdown (Mikkeli, 19 vs. 7, P < 0.001; Kuopio, 9 vs. 2,5, P < 0.001). The influenza season was shorter (8 weeks from peak to no cases), and the weekly rate of new cases decreased faster compared with the previous 4 influenza seasons (previously 15–20 weeks from peak to no cases). A similar decrease was also seen in RSV cases. No pediatric cases of COVID-19 were found in participating hospitals during the study period. Conclusion: These results strongly suggest that social distancing and other lockdown strategies are effective to slow down the spreading of common respiratory viral diseases and decreasing the need for hospitalization among children.

Hospitalization for bronchiolitis in infancy is associated with an increased risk of asthma, and an increased use of asthma medication in adulthood at the age of 28-31 years. Impaired respiratory health-related quality of life in adulthood as measured by the SGRQ is present after bronchiolitis and pneumonia in infancy.

Children with RV- or RSV-induced wheezing in early childhood have an increased risk for asthma and lung function abnormalities in adulthood.

Respiratory tract infection LRTI hospitalisation in infancy was associated with an increased risk of permanent obstructive lung function reduction in adulthood. The asthma risk was higher after hospitalisation for bronchiolitis, than in the controls, and respiratory health-related quality of life was lower after hospitalisation for pneumonia.