My best friend back in RI has two autistic sons. The state was trying to force her to put both her sons in a long term care hospital. She refused to do it. It became a long battle with the state, but she went to law school, got her degree, passed the bar, and is now fighting the state. She also helps other parents who live in other states who have similar issues as hers.
The reason I brought that up is because she doesn't necessarily believe vaccines are always the cause of autism. She feels it's more a combination of things.
As for the chicken pox vaccine, I just don't think it works for everyone. In my own daughters case it sure didn't, and I know of other kids who the vaccine didn't really seem all that effective. Just keep an eye on your little guy. He'll probably be fine, but just be aware in case he's around chicken pox. You'll at least know what to look for.
Bluemoon