Humoral and T-cell immune response against SARS-CoV-2 in children with acute respiratory infections

Objective. The aim was to evaluate specific T-cell and antibodies against SARS-CoV-2 in children hospitalized with respiratory infectious diseases.Materials and methods. Examination of 121 children was carried out in 2021–2024. Among them 22% of patients were under 1 year of age, 33% — 1–3 years, 21% 4–6 years, 24% 7–14 years. In 51 children acute respiratory infection was concomitant with the course of pertussis. Diagnosis of acute respiratory viral infections was based on clinical data and on PCR testing of nasopharyngeal mucus including PCR testing for SARS-CoV-2. Using a method we developed, memory T cells specific to the SARS-CoV-2 S-glycoprotein were assessed in patients' blood. IgG- and IgM-antibodies to SARS-CoV-2 S-glycoprotein in blood serum were also tested.Results. IgG antibodies to S-glycoprotein SARS-CoV-2 were detected in the blood of 55% of children in 2021, 65% in 2022, 82% in 2023, and 96% in 2024. T lymphocytes activated by stimulation with recombinant S-glycoprotein SARS-CoV-2 were detected in the blood of 25% of children in 2021, 70% in 2022 and 19–35% in 2023–2024. A significant (55%) frequency of serologic markers of transmitted undiagnosed COVID-19 was found in children under 3 years of age whose contacts, especially in 2021, were limited to family. In the groups of patients 3–14 years old, even more children were seropositive (95–100%). Memory T cells were found less frequently in children younger 3 years than after 3 years of age.Conclusion. Examination of individuals with various respiratory diseases can clarify ideas about what part of the population has acquired immunity against SARS-CoV-2, as well as assess the role of memory T cells and antibodies to “ancestral” and current strains of SARS-CoV-2 in limiting morbidity.