A lot of the current vitriol aimed at vaccines can be traced back to reports of autism links in the 1990s. The association has remained lodged in the minds of many even as research has discredited the original paper and consistently found no link between vaccines and autism.
Research published in Pediatrics has added to evidence that there is no link between the administration of vaccines in childhood and autism. The paper, funding for which came from the Centers for Disease Control and Prevention, looked at antibody counts in more than 1,000 kids, 25% of who had autism. There was no correlation between antibody count and incidence of autism up to the age of two when the first vaccine schedule ends.
The researchers focused on antibody count to assess the credence of claims that the sheer number of vaccines now given to children is behind alleged autism links. Discussion of the theory gained pace in 2004 after a paper found no causal link between autism and either the measles, mumps and rubella vaccine or thimerosal. With evidence mounting against these two then-popular lines of argument, the "too many vaccines" theory grew in popularity.
Now this theory must contend with contradictory data. As well as finding no correlation between antibody count and autism, the researchers also note that changes to vaccines can further allay fears. In the 1990s, when the vaccinations assessed in the paper were given, the immunization program exposed kids to thousands of antigens. Now, the whole infant vaccination schedule has 315. As Forbes and the researchers note, some antigens have more impact than others, but in terms of scale vaccines are inconsequential. Children are exposed to hundreds of viruses and other antigens from birth onward. In theory, a child could respond to thousands of vaccines at once.