Tamiflu is most effective when taken within the first 48 hours of the onset of symptoms. It does not treat the flu. It reduces the severity and length of illness. You are still contagious for 7 days after the symptoms began, even if you feel better. I was taking tamiflu as a preventative since a coworker knowingly came in with the flu and after 3 doses my bowels were in a terrible uproar. I was to take it once daily for 10 days and on day five could not stand the diarrhea any longer and quit taking it. A: About seven days after flu symptoms begin, people with compromised immune systems or the conditions listed above are at risk of developing a secondary bacterial infection. In some cases, this. Flu symptoms typically last about one week, but may linger for some people. We explain what to expect when you have the flu, how long you’re contagious, and signs of complications. How long does the flu last then? As long as you managed to do this within the first 48 hours of your symptoms appearing, treatment with Tamiflu can shave about a day off of your flu symptoms. My son came down withH1N1 this week but the test did not come back for five days in which is to late to use Tamiflu. They recommend using within the first 48 hours of symptoms. All symptoms of the flu are usually gone in 7 to 10 days, although sometimes a cough can last fo … r a couple of weeks after the other symptoms are gone. ( Full Answer ) share with friends However, Tamiflu only works if taken as directed, which means you must take Tamiflu within two days of noticing symptoms. If you are taking Tamiflu to prevent the flu from developing, it may work continuously and you may not have any flu symptoms. How long do flu symptoms last? ANSWER Most flu symptoms gradually improve over two to five days, but it's not uncommon to feel run down for a week or more. A common complication of the flu is. How Long Is the Flu Contagious? A 2013 survey conducted by the National Foundation for Infectious Diseases revealed that 41 percent of people think the flu is only contagious after symptoms start.1.