Dr. Stevan Cordas Dr. Cordas. 1  Contagious: 24 hours after you are done having a fever whether you take tamiflu (oseltamivir) or not (without anything to take away the fever). 2  Take good precaution: It is hard to say if you are still contagious, maybe not. 3  Flu: You are contagious with a fever and a few days after.