The Development History, Structural Composition, and Functions of Influenza Viruses and the Progress of Influenza Virus Inhibitors in Clinics and Clinical Trials

Flu is an acute respiratory disease caused by influenza viruses. The influenza viruses are classified as Alphainfluenzavirus (influenza A virus, IAV), Betainfluenzavirus (influenza B virus, IBV), Gammainfluenzavirus (influenza C virus, ICV), and Deltainfluenzavirus (influenza D virus, IDV) according to the antigenicity of nucleoproteins (NPs) and matrix (M) proteins in vivo. It is estimated that the seasonal influenza epidemics will cause about 3-5 million cases of serious illness and 290,000–650,000 deaths in the world every year, while influenza A virus is the leading cause of infection and death. Neuraminidase (NA) is one of the most critical targets for the development of anti-influenza virus drugs, and the main drugs clinically applied for the treatment of flu are neuraminidase inhibitors. However, various mutant strains have developed resistance to these inhibitors (For example, the substrains of H274Y in H1N1, H5N1, and E119V in H3N2 have developed resistance to Oseltamivir). Influenza viruses mutate frequently, and new substrains emerge constantly, and the pandemics caused by the new substrains will break out at any time. Therefore, it is urgent to develop new and wide-spectrum influenza virus inhibitors for overcoming the emerging influenza pandemic. Here, we focus on describing the progress of influenza virus inhibitors in clinics and clinical trials to provide a comprehensive reference for the researchers.