My personal experience;
Everytime I am in contact with a person who has a cold or flu - I get it! And my flu is always 10 times worse than the person that I got it from (often, I end up hospitalized because I get a horrible viral infection also!)
There are conflicting opinions about Lupus patients getting the flu shot. But, I get one ever year and when any of my friends or family members get sick, I avoid them like the plague (fortunately, they all understand why I do this). Even my husband...when he gets sick, I move into the guest bedroom :?
The reason I avoid persons with the flu is because, most often, flu is spread by breathing in droplets expelled into the air by an infected person's cough. These droplets can land in your eye or nose; or they get on your face and you touch your face and then touch your mouth or rub your eyes or scratch your nose. If you shake hands with a person who is coughing or sneezing, the flu is spread that way (it would be a good idea to wash your hands). You can also get the flu from sharing cups, glasses, or other household objects used by a person who has the flu.
With reference to the incubation period; When you get infected with the flu virus, it multiplies quietly in your body until you get symptoms of the disease and start excreting enough virus to give to someone else. That's the incubation period. For the flu, it is about two to five days. So if you are exposed today, you probably won't have any symptoms for three to five days. Then you have a little headache, maybe a few aches and pains and maybe a low fever. Then, the next day, you have a high fever and a runny nose and then it goes downhill from there.
Most adults are contagious for about five to seven days. With young children, it's longer. The youngest kids (1 to 2 year olds) can be contagious for 10-14 days. And they can also have diarrheal illness when they get the flu. They get more symptoms that we adults typically have.
Note: According to the CDC, people with lowered immune systems (Such as people with Lupus) or people taking drugs to immunosuppressant drugs, can be contagious for weeks or months after infection.
I hope that I've answered your question
Peace and Blessings