Influenza remains one of the most common respiratory viral diseases with a high risk of complications. In the context of the COVID-19 pandemic, there is a possibility of simultaneous circulation of two viruses, which makes it necessary to conduct a differential diagnosis. Influenza and COVID-19 have common pathways of transmission of the pathogen and similar symptoms, so the optimal differential diagnosis is the use of test systems for both viruses. Against the background of influenza and COVID-19, complications from various organs and systems can develop. The article describes in detail the complications of influenza from the cardiovascular system. After infection with the flu virus, there is a 6-to 10-fold increase in the risk of acute myocardial infarction and a 3 - to 8-fold increase in the risk of stroke. COVID-19 is associated with arterial hypertension, diabetes mellitus, cardiac arrhythmias, myocarditis, high risk of acute myocardial infarction, and heart failure. The article presents the data of our own research, indicating that the transferred COVID-19 disease increases the risk of acute coronary syndrome, regardless of the presence of risk factors for cardiovascular events. Prevention of the development of influenza complications is the early administration of etiotropic antiviral therapy. Numerous studies confirm the effectiveness of the neuraminidase inhibitor oseltamivir in the treatment of influenza. The use of oseltamivir reduces the severity of clinical manifestations, reduces the duration of the disease, reduces the risk of complications and death. The most effective measure to prevent influenza and COVID-19 is specific immunization. In some cases, chemoprophylaxis can be used. The article discusses studies on the effectiveness of influenza chemoprophylaxis with the use of neuraminidase inhibitors.