Immune Response to SARS-CoV-2 Infections in Children with Secondary Immunodeficiencies

Background and Purpose It is a matter of research, whether children with immunodeficiencies are able to generate an effective immune response to prevent SARS-CoV-2 reinfection. This study aimed to evaluate and compare the seroconversion rates and changes of lymphocyte subsets during COVID-19 in immunocompetent children and those with secondary immunodeficiencies. Methods In 55 children - 28 immunocompromised and 27 immunocompetent - hospitalized with confirmed SARS-CoV-2 infection, the level of IgG antibodies against the Spike protein was determined on two to three occasions. In those children from the study group whose immunosuppressive treatment did not alter during the study (n = 13) and in selected children from the control group (n = 11), flow cytometric evaluation of lymphocyte subsets was performed twice - 2 weeks and 3 months post-infection. Results Seroconversion reached 96.3% in both studied groups; however, the immunocompromised cohort achieved lower titers of detectable anti-S antibodies. There was no correlation between seroconversion or titers of antibodies and the total number of lymphocytes or their subsets. In the immunocompetent cohort, we reported a significant decrease in NK cells during the infection. In this group and the entire study population, a positive correlation was noticed between the CD4 + /CD8 + T cell ratio and the severity of COVID-19 pneumonia. Conclusions Children with secondary immunodeficiencies seroconvert in equal percentages but with a significantly lower titer of anti-S antibodies compared to their immunocompetent peers. The lower number of NK cells in the immunocompetent cohort may result from their participation in antiviral immunity, whereas reduced CD4 + /CD8 + T cell ratios among immunocompromised children may be a protective factor against a severe COVID-19.