The contoversy around the MMR vaccine and the link to autism is not the mercury as some would think. There is no Thimerisol in the MMR vaccine. The MMR vaccine contains the LIVE antagonist. The theory is, some children do not have immune systems stong enough to battle the diseases properly. A large number of children have a mild version of the illness then proceed to fight it on their own. With the regime of shots our kids get now compared to when we (or at least older moms like myself) got shots as children there weren't as many diseases to vaccinate, nor were there booster shots like today. If you go to the FDA website they have listed every vaccine and whether it is live or not and whether it contains Thimerisol or another preservative. They also have links to studies that have been done to date. Keep in mind this subject has had very little funding and most of the studies are conducted by the manufacturer of the vaccine, at least it was when I looked at them last. Do what you think is best in your heart.