This is another big myth. Just because you don’t have symptoms right away doesn’t mean that the virus is not in you. That’s why it’s important to know that you can pass it to someone before you feel sick. So practice good hygiene. It can take up to a week for you to start feeling bad and you are most contagious during the first 2-3 days. Between 20 and 30 percent of people with the flu virus don’t experience symptoms.