I'm one of those people who's rarely affected by mosquitoes - but I'll still get bit. I'd estimate I get 1 bite for every 5 that anyone else I'm hiking with does. People will be complaining about how bad the mosquitoes are and I'll have ~0-2 bites.

So in my case, I do have a response to at least some bites, but consistently fewer than anyone else I'm with.

Mosquitoes rarely bite me unless I'm their only option. They won't bite me at all if someone else is in the vicinity (so, my poor girlfriend).

You can quickly confirm whether it's no biting vs no reaction by the fact that you can see them flying around and landing on you. Or rather, around everyone else except you. They aren't invisible. Here in the tropics, other people will be covered in them.