Please read the study at the link I provided, which will answer your questions.
Whatever happened to natural immunity build up. When my friend’s daughter was 5, she got the chicken pox. I sent my daughter to stay overnight and specifically told my friend to put her in he bath with her daughter. Sure enough, my daughter got it and was out 1 week of Kindergarten. Then my son, 2 years younger was put in the bath with his sister and he got, but wasn’t in school yet so didn’t miss any class.