A link has been postulated between the specific use of the triple MMR vaccine and the rise of childhood autism. Though very considerable research has shown there to be no connection, some people continue to believe in such a link and they propose use of single vaccines instead. In Japan, MMR vaccine was introduced in 1989, but the programme was terminated in 1993 and only single vaccines used thereafter.

The experience of Japan therefore constitutes a real-world experiment of replacing triple MMR vaccine with single vaccines because of problems with production. If the proponents of a link between MMR and autism are correct, the result should be that cases of autism fall after withdrawal of MMR.

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