The COVID-19 pandemic, through the restrictions and the non-pharmaceutical interventions implemented, has importantly impacted the circulation and epidemiology of respiratory viruses. Specifically, the 2020/21 season was entirely dominated by SARS-CoV-2, while influenza activity reached an all-time low, despite initial warnings that a double concurrent epidemic could be possible. The current season, 2021/22, started with the shift of circulating SARS-CoV-2 variants from delta to omicron, which then rapidly spread globally, as most countries, including Romania, removed all restrictions and compulsory non-pharmaceutical interventions. In this report we present the clinical reality observed in March 2022 in a tertiary paediatric hospital in Bucharest, Romania, where we observed a sudden surge in influenza cases, after two consecutive years (March 2020 to March 2022) when influenza had stopped circulating in our country. Thus, in March 2022 the positivity rate of rapid influenza antigen tests unexpectedly increased to 33.5%, paralleled by a decrease to 7.5% in the positivity rate of rapid SARS-CoV-2 antigen tests. This significant increase in the influenza attack rate was observed from the first week (14.9% positivity rate), through the fourth week of March (42.1% positivity rate, p < 0.001), while the COVID-19 attack rate displayed a significant decreasing trend (from 11.2% to 4.8%, p < 0.001). These data serve as a warning about relaxing restrictions in a precipitous approach with minimised vigilance. The evolution of these observations needs to be followed very carefully in all countries, particularly in settings where epidemiological interactions and non-pharmaceutical interventions have so far led to the extensive circulation of only one of these viruses, and we should now be prepared to perform a correct differential diagnosis between influenza and COVID-19, in order to ensure the best quality of care and personalized management of each case of respiratory infection. The results of active influenza surveillance studies for the whole 2021/22 season are awaited, in order to quantify the joint influenza—COVID-19 burden among children.
Keywords: COVID-19; SARS-CoV-2; children; influenza; omicron.