Don't crucify me, just adding our experience with this situation so far this year.
Had a dcm test positive for influenza a couple weeks ago. Dcg is 15 mos and continued to come for the week dcm was down. I even had to ask dcm once to not come in my house when she came to drop off so she could get rest.
No one else here, including dcg got sick.
DH has had the flu go through his work place, and we have still managed to avoid it.
I have been hesitating to type of any of this because I know as soon as I do it will hit us... but so far so good. So maybe, just maybe, its not guaranteed that everyone will get it.