Many expectant parents are wary of all the recommended vaccines their newborns are supposed to get in the first hours, days and even the first couple of years, believing that too many vaccines too soon may increase their child's risk for autism.
A new study published in the Journal of Pediatrics Friday may put them at ease. Researchers found no association between autism and the number of vaccines a child gets in one day or during the first two years of the current vaccine schedule.
The research was led by Dr. Frank DeStefano, director of the Immunization Safety Office at the Centers for Disease Control and Prevention. Together with two colleagues, DeStefano and his team collected data on 256 children with autism spectrum disorder (ASD) and 752 children who did not have autism. The children were all born between 1994 and 1999 and were all continuously enrolled in one of three managed-care organizations through their second birthday.
The researchers not only counted how many vaccines a child was given, they also counted how many antigens within the vaccines children were exposed to over three different time periods: birth to 3 months, birth to 7 months and during the first two years. They also calculated the maximum number of antigens a child would receive over the course of a single day.
An antigen is an immune-stimulating protein found in a vaccine that prompts the body's immune system to recognize and destroy substances that contain them, according to the NIH.
Some vaccines, like Hepatitis B, only contain one antigen for this one virus. However, at the time these children were vaccinated, the typhoid vaccine had 3,000 antigens per dose and the measles, mumps, rubella (MMR) vaccine had 24.
"When we compared those roughly 250 children with ASD and the roughly 750 children who did not have ASD, we found their antigen exposure, however measured, were the same," said DeStefano. "There was no association between antigenic exposure and the development of autism."
The researchers also found no association between antigenic exposure and ASD.
Geraldine Dawson, chief science officer of the science and advocacy group Autism Speaks, called the research a "well-done study." She was not affiliated with the research.
"The big challenge that we face is the fact that we still don't understand the causes of autism -- genetic or environmental," she said. "So while this answers one question parents may have, we still have many more to be addressed."
Dawson and DeStefano both believe the study should be reassuring for parents concerned about the vaccine schedule. Vocal critics have argued that children receive too many vaccines too soon, and that the frequency of the shots is one factor in why some children develop autism.
"I would tell an expectant mom that one of the more important things you can do to protect an infant's health is get them vaccinated on time according to the recommended schedule," DeStefano said. He says vaccines protect against serious life-threatening diseases and delaying them can put your child unnecessarily at risk.
"The bottom line is the number of vaccines, or the number of antigens in the current schedule, given on time ... is not associated with a risk of autism."
In 2011, the British medical journal BMJ said a now-retracted study linking autism to the vaccine that prevents measles, mumps and rubella was an "elaborate fraud" that did long-lasting damage to public health. An investigation by the journal said the study's author, Dr. Andrew Wakefield, misrepresented or altered the medical histories of all 12 patients whose cases formed the basis of the 1998 study.
Wakefield told CNN's "AC360" that his work had been "grossly distorted" and he was the target of a "ruthless, pragmatic attempt to crush any attempt to investigate valid vaccine safety concerns."
The now-discredited paper panicked parents and led to a sharp drop in the number of children getting the vaccine. Measles cases increased in the ensuing years.
Caitlin Hagan | CNN