The correct answer is option 1 - bird flu. Tamiflu is a frontline antiviral drug primarily used to treat and prevent the influenza virus, including certain strains of bird flu (avian influenza). Bird flu is a type of influenza that primarily affects birds but can also be transmitted to humans in rare cases. Tamiflu works by inhibiting the reproduction of the influenza virus, reducing the severity and duration of symptoms, and preventing complications. It is important to note that Tamiflu is not effective against other viral infections like cancer, AIDS, or polio. It is specifically designed for treating and preventing influenza, including bird flu.