I have two comments:

1) There is nasty strep going around our state. Some people have had it more than once... it returns! The kids are getting it in school and bringing it home to adults.

2) If your Vit D is very low, your immune system will not respond properly to invaders like strep or viruses.

Autoimmune disease MAY mess up normal responses to invaders. If your body is using up its resources to ramp up attacking itself, there may not be much left over for the real job of protecting you from invading organisms.