I didn't have immunity to CP either and after a lot of thought decided to get it done. I just decided it was better to be safe and it can be a lot worse as an adult. I went through the same arguements against having it that I haven't caught it over the last 27 years, but figured I am likely to catch it sometime in the future if I have kids so it was best to get it done now. It was only 1 injection and I didn't have any reaction to it and we just had to wait 1-2 months before TTC.