I don't understand how you think cats can catch just as many diseases inside as outside I don't know about you, but I don't have dozens of stray cats walking through my house every day. So since Shiloh is inside, she is never exposed to strange cats, therefore she can't catch anything. If she went outside, I would have no clue which cat's feces she'd be walking in and what she'd catch.

And vaccinations aren't 100% effective.