When you are exposed to the influenza virus, you don't immediately get sick. The amount of time between the moment the virus enters your body until you start to experience symptoms is called the incubation period. The incubation period is different for different illnesses.
Having this information is important because you will want to know how long it might take to get sick if you are exposed to the flu. For example, if you go to visit your second cousin's best friend's brother who ends up having the flu, you will want to know how long you have to wait to find out if you will get sick too.
Find out what the incubation period is for the flu, as well as what to do to avoid getting it and how long you will be contagious if you do get sick.