Clinical course of COVID-19 in hospitalized children of Ukraine in different pandemic periods.

Background: The coronavirus infection (COVID-19) pandemic has seen a progressive increase in childhood morbidity worldwide. Continuous mutation of the SARS-CoV-2 virus causes the wave-like course of the COVID-19 pandemic, which is characterized by an undulating course and the predominance of different variants of the SARS-CoV-2 virus. There are many reports that the clinical picture may vary depending on the circulating strain of the virus [7-11, 13-16].