>>”...is there an anti-vaxxer in existence who can propose a rational, scientifically accurate, testable biological mechanism by which vaccines could cause autism?”<<
Actually, Dr. Cannell, who is not an “anti-vaxxer” by any means, has proposed a rational, testable, link between vaccinations and autism which depends upon the child being deficient in vitamin D plus being genetically predisposed to autism. (The link hasn’t been tested, but it is testable, although such a test would conceivably be unethical if it involved leaving a placebo group with a severe vitamin D3 deficiency.)
His point is that the genes predispose a child to autism and that the condition itself is triggered by a combination of a weakened immune system caused by the D3 deficiency followed by the insult of a heavy dose of vaccinations. Personally, I think he’s onto something, and present research (as discussed in a post further up in this thread) is supportive of his thinking, which he has held since 2007 when I first encountered his ideas on autism. I found his theory very interesting at the time because it explained several of the various explanations for the observed increase in autism rates
Within this situation, however, is nothing that implicates vaccines--even given the association of low vitamin D and autoimmune disorders. Any particular vaccine only contains a handful of antigens--contrast that with the thousands of antigens babies encounter every day. Who has not seen babies pick up filthy objects from the ground or floor and pop them in their mouth? How many millions of bacteria, fungi, and viruses do they thus ingest every day? If exposure to those thousands or millions of antigens (with the resulting immune system activation) does not cause neurological disease, then the estimated 350 antigens total that a child receives throughout the vaccine schedule are not going to cause a problem.
It would certainly be nice if autism could be traced back to some flaw in the vitamin D system. Certainly, it would be a simple matter to test for vitamin D levels in pregnant women and newborn babies and supplement them if necessary. It would be like the discovery that folic acid prevents certain birth defects. Plus, it would take away one of the favorite scare tactics of the anti-vaxxers and force them to come up with some other way to scare parents into willingly exposing their children to dangerous brain-damaging and even lethal diseases.