The Wakefield Study: Controversial research by Andrew Wakefield in the UK, published in The Lancet in February 1998 suggested a possible link between autism and the MMR vaccine. The original research has come under criticism, largely due to a conflict of interest on Wakefield's part. In February 2004 The Lancet described the research as "entirely flawed", said that it should never have been published, and 12 of the original 14 authors of the paper retracted their claims. Critics with statistical skills have claimed that Wakefield's study contains many obvious flaws, including an inability to recognize bias in his sample. Controversy continues, with Wakefield continuing to defend his theory.

Contradictory evidence: Although the fact that the Wakefield study is flawed does not in itself prove that no autism-vaccine connection exists, further research suggests that the theory is most likely false. Several independent groups have conducted thorough investigations into the possible link, including the National Academy of Sciences, and concluded that the evidence does not support a link between the MMR vaccine and autism. Studies that offer contradictory evidence include:

• A study by Gillberg and Heijbel (1998) examined the prevalence of autism in children born in Sweden from 1975-1984. There was no difference in the prevalence of autism among children born before the introduction of the MMR vaccine in Sweden and those born after the vaccine was introduced.
• Madsen et al. (2002) conducted a study of all children born in Denmark from January 1991 through December 1998. There were a total of 537,303 children in the study; 440,655 of the children were vaccinated with MMR and 96,648 were not. The researchers did not find a higher risk of autism in the vaccinated than in the unvaccinated group of children.
• A study by Gillberg and Heijbel (1998) examined the prevalence of autism in children born in Sweden from 1975-1984. There was no difference in the prevalence of autism among children born before the introduction of the MMR vaccine in Sweden and those born after the vaccine was introduced.
• Research in the US suggesting a similar link between autism and DPT vaccine. It isn't however the large majority of autism that would come from vaccines, unlike early claims from Wakefield.