Yes check with your cf specialist (not regular dr as they can overreact to the cf dx and hesitate on important issues). The flu shot is not a live virus so you *cannot* get sick from the shot. In general, the risk of getting the flu for someone with cf (and the very young, and the very old, and those with respiratory problems) is far greater than the risk from any side effects from the shot. It's November and we've had flu show up already in Maryland. It takes about 2 weeks for the shot to be 'protective' so I'd try to resolve this sooner rather than later if I were you. You are probably fine getting it, but your cf spec can guide you best.