China has been using Avigan on patients and it has worked.
There is not a scientific study that supports this statement at all. Clinical trials of favipiravir has been non-conclusive. Meaning that they can't rule out other factors such as time, or effects on mortality rate. There are clinical trials underway but so far it's way too early to make any such statements. I have an extensive laymans interest in this field and my gf has a phd in the field and currently works as a researcher, so this is a fairly frequent topic at home.
Early study reports from the trial group have indicated that fever has gone away shortly (2-3 days) after taking the drug, but the study has shown no effectiveness in treating covid-19 early. Meaning that the patients who report their fever clearing may just have ended the course of the illness regardless of administration.
There is a current study in India that yields more positive data, but its still very early. Favipiravir (Sold under the brand name Avigan) is only meant to treat mild to moderate symptoms, this is not a cure for patients who are at the point where they experience severe respiratory problems.