Nothing is guaranteed. There is a chance that if you contract the disease, that it won't be as bad. A chance. No 2 people are the same. The same as there is a chance the immunisation won't fully protect you.

From what you have described, your DS has a mild dose. I don't know if he's in the early stages or not though.

DD2 had them at 6 months old & they were pretty nasty. It was an absolute nightmare. None of my other children have contracted CP though, despite the fact that I'm 99% sure DD1 brought them into the home.