A US study out Friday sought to dispel the fears of about one third of American parents that giving a series of vaccines to children may be linked to autism.
Even though children are receiving more vaccines today than they did in the 1990s, there is no link between "too many vaccines too soon" and autism, said the study in the Journal of Pediatrics.
About one in 10 US parents refuse or delay vaccinations for their children because they believe it is safer than following the schedule put out by the Centers for Disease Control and Prevention, according to previous research.
Prior studies have already shown there is no link between vaccines and autism, including a 2004 comprehensive review by the Institute of Medicine.
This time, researchers at the CDC decided to look children's exposure to antigens, the substances in vaccines that cause the body to produce antibodies to fight infection and disease.
Researchers looked at data from 256 children with autism spectrum disorder across three separate managed care organizations in the United States.
They compared the cumulative exposure to antigens in those children to 752 children without autism.
"We found no evidence indicating an association between exposure to antibody-stimulating proteins and polysaccharides contained in vaccines during the first two years of life and the risk of acquiring autism spectrum disorder, autism disorder or autism spectrum disorder with regression," said the study.
Nor were there any links between autism and cumulative exposure to antigens, either from birth to two years of age or within the course of a single day after receiving multiple vaccines at the doctor's office, it said.
"These results indicate that parental concerns that their children are receiving too many vaccines in the first two years of life or too many vaccines at a single doctor visit are not supported in terms of an increased risk of autism," it said.
Autism affects as many as one in 88 in the United States and about one in 100 in Britain. The brain disorder has no single known cause but experts believe it may be triggered by a combination of genetics and environment.