Age of Autism's latest
This is only one of many times I have seen the AoA take wording which is scientifically conservative, or only there to placate the very people at the Age of Autism, and make it sound like the CDC (or whomever they are talking about) is unsure about the certainity of Autism and vaccine research. This is just another example of the he "Only a theory " tactic used by creationists against evolution, though slightly more nuanced. It is simply impossible to rule out anything 100% and this statement reflects that.
In this case the CDC mentions on it's website
"There is some evidence that the critical period for developing ASDs occurs before birth. However, concerns about vaccines and infections have led researchers to consider risk factors before and after birth."
All that is admitted to by this statement is that the very vocal anti vaccine crowd has caused enough of a panic to keep to this research area alive. It states nothing about the certainty of the conclusions or even the nature of the risks that are being considered. Vaccines are only being implied as the impetus for this research.