How Tamiflu fights the flu virus?  Tamiflu (oseltamivir) is an antiviral drug used to treat flu symptoms caused by Influenza virus types A and B in your body. Tamiflu works by blocking the actions of Influenza virus in people who have had symptoms for less than 2 days. Tamiflu use can also help to prevent the virus in people who may be exposed to the virus but do not have any...