ATLANTA, March 29 (UPI) -- U.S. researchers say there is no association between receiving "too many vaccines too soon" and autism spectrum disorder.
Dr. Frank DeStefano and colleagues at the Centers for Disease Control and Prevention and Abt Associates, Inc. analyzed data from 256 children with autism spectrum disorder and 752 children without autism spectrum disorder born from 1994-99 from three managed care organizations.
They looked at each child's cumulative exposure to antigens -- the substances in vaccines that cause the body's immune system to produce antibodies to fight disease -- and the maximum number of antigens each child received in a single day of vaccination.
The researchers determined the total antigen numbers by adding the number of different antigens in all vaccines each child received in one day, as well as all vaccines each child received up to age 2.
The study, published in The Journal of Pediatrics, said the total antigens from vaccines received by age 2, or the maximum number received on a single day, was the same between children with and without autism spectrum disorder.
An infant's immune system is capable of responding to a large amount of immunologic stimuli and, from time of birth, infants are exposed to hundreds of viruses and countless antigens outside of vaccination, the researchers said.
"The possibility that immunological stimulation from vaccines during the first one or two years of life could be related to the development of autism spectrum disorder is not well-supported by what is known about the neurobiology of autism spectrum disorders," the study authors wrote.
Despite earlier scientific evidence suggesting vaccines didn't cause autism, approximately one-third of U.S. parents expressed concern that they do; nearly 10 percent parents refused or delayed vaccinations because they said it was safer than following the CDC schedule.