As my nephew would say "correlation is not causation."
And it is a fundamental truth of science inquiry.
That is true, however epidemics are always caused by a change in the environment. When you have a dramatic increase in autism rates from 1 in 100,000 to 1 in 36 over a 40 year period you have to look at what has changed dramatically in the environment.
One thing that has changed is childhood vaccines increased from 5 in 1980 to kids will get 60 shots today by the time they are 12.
By itself that is not proof of causation, but it is more than sufficient reason to justify a serious double blind scientific study into this.
People saying we don't have any proof that it is the vaccines causing the autism is like Bernie Madoff saying we don't have any proof he is running a pyramid scheme prior to us getting to look at his books. We don't have proof but we do have sufficient reason to justify doing a study.