First, take some good immune system support supplements. Vit C 5000-10,000 mg per day is one of the best. There are others like Thymus, and herbs specific for infections.

Second, if the bug is viable, then the cabin crew would be getting sick, if their immune system is weakened. I know a lot of them take extra vitamins to help with the stress of flying. The bug does not know who the passengers are and who the Flight crew are!