Systemic lupus erythematosus (SLE) is an autoimmune rheumatic disease of unknown etiology, characterized by overproduction of organ-nonspecific autoantibodies to various components of the cell nucleus and cytoplasm and the development of immune-inflammatory damage to internal organs. The debut of SLE is preceded by an asymptomatic period, characterized by impaired immunological tolerance to its own autoantigens, determined by the multifaceted interaction of external, genetic and epigenetic factors, hormonal disorders, microbiome pathology, stress effects, etc. Development of a certain spectrum of clinical symptoms characteristic of SLE along with the detection of a reflects the progression of the immunopathological process in SLE, however, there is no generally accepted term that defines the patient’s condition, which has individual serological and clinical signs characteristic of this disease. In rheumatology, the concept of «incomplete» SLE is currently most often used. The problems of early diagnosis of SLE, clinical and laboratory predictors of the transformation of “incomplete” SLE into “reliable” SLE, difficulties in diagnosing SLE during the COVID-19 pandemic are considered. Particular attention is paid to the comparative characteristics of the immunopathological mechanisms of SLE and COVID-19.