Parents can rest assured that getting kids their vaccine shots on time will not hurt their mental skills later on, doctors said on Monday.
"A lot of parents are concerned that children receive too many vaccines too soon," said Dr. Michael J. Smith, of the University of Louisville School of Medicine in Kentucky. Some parents skip recommended vaccines out of fear of autism, for instance, and some choose to space out shots.
Although there is no evidence that would be safer, Smith said, he wanted to study the issue to address parents' concerns. So he and a colleague tapped into data from more than 1,000 preteen kids who had undergone extensive psychological tests of IQ, memory, attention, and language.
Then they divided the kids into those who had received all their shots on time in their first year of life and those who got them late, or only got some.
"Those children who were late, they never did better in any analysis," said Smith, whose study is published in the journal Pediatrics.
In fact, when comparing kids who had received the largest number of vaccines as toddlers against those who had received the smallest, the first group scored higher on 15 out of 42 tests.
But when the researchers took factors such as parents' education level into account, that difference disappeared for all but two tests. And for those, the difference was minimal, Smith said.
Earlier studies based on the same data had shown that the mercury compound thimerosal, which was used as a preservative in vaccines until recently, had no impact on kids' mental skills.
But until now, nobody had studied whether getting several vaccinations in a short time could have negative consequences, for instance by overloading the immune system, as many parents believe, according to Smith. He found that receiving as many as 10 different shots — including flu and whooping cough — had no impact.
A Centers for Disease Control and Prevention researcher said the new findings send an important public health message.
"Parents that are considering delaying vaccination should realize that there aren't any specific benefits, and that they are putting their child at risk, and not only their child but also the community," said Dr. David Sugerman, of the CDC's Epidemic Intelligence Service in Atlanta.