Antiviral medications for mild-to-moderate COVID-19 in Japan: a gap of timing between clinical trials and real-world scenarios in a fast-changing pandemic.

The rapid spread of a novel type of coronavirus infection, coronavirus disease 2019 (COVID-19) has made it difficult to implement the results of clinical trials in real-world situations. After the emergence of the Omicron variant and messenger RNA vaccine, a combination of less virulent but more contagious viruses and more people with protective immunity has resulted in a larger number of patients with less severe, mild-to-moderate COVID-19. Many patients with severe conditions did not have extensive viral pneumonia frequently seen in the "pre-Omicron" era but had serious complications due to aggravation of underlying comorbidities or secondary bacterial infections. Most clinical trials for new antiviral drugs were conducted in the "pre-Omicron" period based on a different set of background patient characteristics than the ones seen in the Omicron period. Understanding situational differences due to the gap in the timing between clinical trials and the practical use of drugs for COVID-19 will assist in developing an effective treatment strategy in real-world practice. In this seminar, we reviewed antiviral treatments for mild-to-moderate COVID-19 from the viewpoint of the difference in patient backgrounds between clinical trials and real-world studies, focusing on drugs currently used in Japan.