COVID-19 and the flu: clinical and immunological features in children

Abstract

In conditions of co-circulation of COVID-19 pathogens and other acute respiratory infections, the risk of simultaneous infection with SARS-CoV-2 and other pathogens, in particular influenza viruses, increases. Previously published data on the mutual influence of such combined infectious processes are very contradictory.Purpose. To determine the clinical and immunological features of the combined course of COVID-19 and influenza in children.Material and methods. Among 3,983 hospitalized children with COVID-19, 48 patients (1.2%) co-infected with influenza A and B viruses were identified by PCR. 31 children with a combination of COVID-19/Influenza were subjected to in-depth examination. The comparison group consisted of 30 children with SARS-CoV-2 monoinfection. In addition to standard physical, instrumental and laboratory studies, serum levels of IgM and IgG to SARS-CoV-2 S protein were determined in patients of the compared groups using ELISA.Results. In children with a combination of influenza and infection caused by both delta and omicron variants of SARS-CoV-2, acute bronchitis was more common, regardless of age, compared with patients with SARS-CoV-2 monoinfection. Co-infection with the influenza virus did not change the incidence of pneumonia in patients with omicron-SARS-CoV-2 infection, and in patients with delta-SARS-CoV-2 infection it decreased it. In co-infected children, the severity of intoxication syndrome and the level of D-dimer in the blood were higher. In addition, patients with a combination of COVID-19 and influenza showed lower concentrations of IgM and IgG to S-protein in comparison with patients with SARS-CoV-2 monoinfection.Conclusion. Co-infection with influenza viruses alters the clinical course of COVID-19, while the nature and vector of changes depend on the SARS-CoV-2 gene variant. A decrease in the severity of the humoral immune response to SARS-CoV-2 in co-infected children was found.