Abstract
The causative agent of varicella virus is widespread. In children, especially with a complicated premorbid background, there is a high incidence of severe forms and complications. Widespread use of specific prophylaxis is necessary. According to WHO estimates, 4.2 million registered cases of severe complications of chickenpox resulted in 4,200 deaths. Severe course of varicella virus, addition of complications and mortality are typical for newborns and individuals with impaired immune system. The following complications were identified in deceased patients with varicella virus: bacterial (55%), pneumonia (54%), hemorrhagic (41%), from the central nervous system (33%). The genetic diversity of causative agent of varicella virus plays a key role in its pathogenicity, epidemiology and response to vaccination. Despite successful vaccination programs, the virus continues to circulate in the population, which emphasizes the need for a deep understanding of its genetic diversity. Genetic diversity of varicella-zoster viruses may influence pathogenicity, immune response, and vaccine efficacy, making it an important subject of research. Global research results in this area highlight the importance of causative agent of chickenpox genetic monitoring for understanding its evolution and developing effective vaccination and treatment strategies. These results may be useful for epidemiologists, immunologists, virologists, and infectious disease specialists.