Most people who catch the flu start to feel sick about 1 to 4 days after being exposed, with 2 days being the most common.
Typical timing
Flu symptoms usually appear suddenly between 1 and 4 days after the virus enters your body, and many sources describe around 2 days as the average incubation period. During this incubation time you can feel completely fine but the virus is already multiplying in your respiratory tract.
When you are contagious
People with flu can generally start spreading the virus about 1 day before symptoms begin and continue for about 5 to 7 days after they start. Children, older adults, and those with weakened immune systems may be contagious for a longer period.
What to watch for and what to do
Early flu symptoms often include sudden fever, chills, body or muscle aches, fatigue, headache, sore throat, cough, and a runny or stuffy nose. If you know you were exposed, it is sensible for the next several days to limit close contact with others, practice good hand hygiene, and seek medical advice promptly if you develop high fever, trouble breathing, chest pain, confusion, or symptoms that worsen or do not start to improve after a few days, especially if you are in a higher-risk group.
