It might be relatable, or not, but I am a school teacher. The first year I taught, I was sick almost constantly. I think you build up a little immunity with exposure. Also, I always get a flu shot, even if it isn't always the right strain, it will help lessen the flu. Finally, I really do use a lot of hand sanitizer. I used to think it was overkill, but after spending a lot of time in a closed space with 35 germ factories, I have gotten to where I use the hand sanitizer before touch any food, etc. On flights, I carry the hand sanitizer wipes. Especially long flights where I will eat.

I still get a lot of little colds and coughs, but I get over them pretty quickly.

You may have gotten the flu from the lady behind you, or you may have gotten it when you shook hands with several people at a meeting earlier. Who knows?

You might find the same tactics will help when you travel a lot in an enclosed space.