The vaccines kids get today are not the ones I got in 1982-86. It's obvious that vaccines prevent disease, but it's also obvious that kids today are increasingly defective- not just with autism, but you never used to hear shit about peanut allergies or gluten intolerance either. Then you have have cancer being up 20% from 1990-2000 and expected to be up another 50% by 2020.
So maybe... something is very wrong.
A lot of that is that some things work too well. Allergies in general happen when a body's immune system sees something harmless as a threat, and reacts against it triggering normal defenses against disease. A usual culprit is that the person wasn't exposed to much when they're young, and so the body wasn't trained to detect it as normal. Our houses are too clean, basically.
We're also getting great medical care when we're young. Go look up statistics of baby survival (and survival of the mom as well if you're interested) and you'll see a dramatic increase since then. It looks like people have been getting worse recently, but realistically, we've been able to save more from immediate death, though not always terribly successful at getting them back to full strength.
Part of what makes cancer more frequent now is more awareness. We're better at spotting it. We're also better at keeping people alive long enough that cancer gets more chances to be seen. It's sad to say, but from an evolutionary sense, we weren't really tested against surviving against cancer. People just didn't live long enough for it to be a big threat.