The situation with the COVID-19 pandemic in the world is still tense. Due to the peculiarities of its pathogens, there is a low efficiency in the use of available specific etiotropic drugs, which leads to the need to search for new active means of combating this dangerous infectious disease. Since the function of T-cell immunity is significantly impaired in COVID-19, it is advisable to find out the effect of correcting this part of the immune response on the course of coronavirus infection. For this purpose, a screening study was conducted to determine the effectiveness of the thymus preparation thymalin in an experiment on laboratory mice infected with murine hepatitis virus, which belongs to the same subgroup of coronaviruses that includes SARS-CoV-2, the causative agent of the COVID-19 pandemic. It was found that the study drug significantly protected infected mice at the level of 45.0–60.0 % compared to the controls and increased the average life expectancy of the test animals by 2.6–5.6 days compared to the control group, which in percentage terms is 51–110 %. The results obtained can serve as the basis for conducting regulated clinical trials with the aim of using this official medicinal product in clinical practice for the prevention and treatment of coronavirus infections in humans, including COVID-19.