Another study done has found no association between vaccines and autism. Mercury, which is used to preserve the medicines, and hasn't been used since 2001, and has been suspected of causing learning disabilities didn't have any correlation to the increased incidence of autism every since.

Researchers published their study yesterday in PLOS One. The study follows recent news from the Wall Street Journal that doctors are "firing" patients who refuse to have their children vaccinated.

Scientists collected urine samples from 54 children with autism spectrum disorders and compared them 115 children from the general population. 28 children with learning disabilities who attended special schools and 42 children who didn't have autism but had a sibling with the condition.

The study looked at heavy metals like lithium, manganese, cadmium and lead as it if often blamed for exacerbating a theoretical genetic pre-disposition for vaccination complications. They found no differences between the group.

Researchers could do 100 more similar studies, but it wouldn't matter. Nothing can change the mind of a parent who believes there's any chance their child might suffer a permanent learning disability as the result of a vaccine.

But if the studies don't find any correlation, why are parents not vaccinating their kids?

[LiveScience]