But Offit says he is "uncomfortable as a scientist" with the committee's methodology. For most vaccines other than MMR, for which very large population studies have been done to specifically examine the vaccine's putative links to autism and other adverse events, "They're looking at case reports and trying to decide whether they think the evidence supports a link," he says. "That's an unusual way to do science, because now you're making it more subjective."
Wright Clayton says that the panel could not estimate the frequency of adverse effects, most of which are too rare to measure without conducting very large and expensive studies.
She adds that there are ways to bolster future reviews, such as clearer rules for access to electronic patient records. "What would be enormously helpful would be the elaboration of guidelines so that when a clinician immunizes a child and some adverse reaction happens, we know what other information we can get to figure out whether the vaccine did it," she says.
This article is reproduced with permission from the magazine Nature. The article was first published on August 25, 2011.