Flu help?.........................…

Ok me, my mom, my brother, and my dad all shared a clarinet today. About 5 hours later my brother started showing flu symptoms. We did an online quiz and it said he has the flu. Sleepy, headache, fever, runny nose. And more. He's been sleeping quite a while now. Now back to my question. So, If you know you're going to get it soon is there any way to prevent it?? Please provide as much info as possible. If it starts in 3 days, then I'll get sick on TAKS day. So HELP!