Post-COVID syndrome in children: whether a change in lymphocyte count is a risk factor for its development?

The aim of the study: to find risk factors for post-COVID syndrome formation based on the analysis of the dynamic leukocyte count, the relative and absolute blood lymphocyte contents. Materials and methods. A retrospective analysis of medical records of children, aged 10–17 years, who were hospitalized during the second wave of the pandemic (January – July 2021) to the CNE “Lviv Regional Children’s Clinical Hospital “Ohmatdyt” with a diagnosis of moderate COVID-19. A total of 46 children were selected, among them 26 children (post-COVID(-) group), who had no symptoms after COVID-19 and 20 children (post-COVID(+) group) who described various complaints related to disfunction of different organ systems, which affected a normal child’s life. Results. All children from the post-COVID(+) group complained of fatigue, about a third of children – headache (30 %), which were not observed before the disease, quarter of children (25 %) had problems with concentrating, one fifth (20 %) – periodically felt unmotivated anxiety. Analysis of the leukocytosis dynamics, absolute and relative lymphocytosis in the control after one week ±2 days revealed no significant changes in these indicators in the post-COVID(-) group of children. While in the post-COVID(+) group, a slight increase in leukocytosis (from 3.9 × 109/L to 4.05 × 109/L, P = 0.13) was accompanied by a significant decrease in the number of lymphocytes, both relative (from 27 % to 16 %, P = 0.002) and absolute (from 1.51 × 109/L to 0.51 × 109/L, P = 0.001). Conclusions. Patients with persistent lymphopenia or hyperlymphocytosis (one week ±2 days) during acute period of COVID-19 represent a “vulnerable cohort” concerning long-term persistence of symptoms, including severe asthenia. The tendency towards normalization of lymphocyte number can be considered as a protective factor for the formation of post-COVID syndrome, while the negative dynamics or its absence – as a risk factor for prolonged persistence of symptoms.