The preservative in question was Thimerosal and they have either completely eliminated it or reduced it to trace amounts in vaccinations, at the outcry of anti-vaccinationists no less, and it has had zero effect on the rates of autism.
The reason we have seen a huge jump in the diagnosis of autism stems from the fact that the range of diagnosis has been broadened to incorporate more or less sever symptoms and the monitoring is a lot higher. We are seeing more autism, basically, because we are looking for more autism. But the anti-vaccinationists got their way, they were wrong and they still cry about it.
Go figure.