February 2, 2009

Researchers see no autism-vaccine link

U.S. researchers have published a review summarizing the many studies refuting the claim of a link between vaccines and autism.

The review, published online ahead of the Feb. 15 print issue of Clinical Infectious Diseases, examined three main hypotheses and showed how epidemiological and biological studies shoot down these claims.

When one hypothesis of how vaccines cause autism is refuted, another invariably springs up to take its place, Dr. Paul Offit of Children's Hospital of Philadelphia, co-author of the review, said in a statement.

The review said the controversy began after a 1998 study published in The Lancet suggested a link between the combination measles-mumps-rubella vaccine and autism. Offit and Dr. Jeffrey Gerber, a co-author who also is on the staff at the Philadelphia hospital, reviewed more than one dozen large studies, conducted in five countries, that used different methodology and concluded data did not support contentions that the the MMR vaccine and autism are linked. The correlation is coincidental because the MMR vaccine is given at the age when autism symptoms usually appear, they concluded.

The researchers also examined seven studies from five countries that showed the presence or absence of thimerosal -- an ethylmercury-containing preservative -- in vaccines did not affect autism rates.

The researchers further examined if the simultaneous administration of multiple vaccines overwhelms or weakens the immune system. The researchers say children's immune systems routinely handle much more than the relatively small amount of material contained in vaccines.