From Nature magazine

Vaccines are largely safe, and do not cause autism or diabetes, the US Institute of Medicine (IOM) said in a report issued today. This conclusion followed a review of more than 1,000 published research studies.

"We looked very hard and found very little evidence of serious adverse harms from vaccines," says Ellen Wright Clayton, chairwoman of the reporting committee and director of the Center for Biomedical Ethics and Society at Vanderbilt University in Nashville, Tennessee. "The message I would want parents to have is one of reassurance."

The report, commissioned in 2009 by the US Health Resources and Services Administration, covers the eight vaccines that comprise the majority of claims filed with the National Vaccine Injury Compensation Program (VICP), which compensates people for adverse health effects from any of 11 vaccines.

The eight vaccines under review were those for chickenpox; influenza; hepatitis B; human papillomavirus; diphtheria, tetanus and pertussis (DTaP); measles, mumps and rubella (MMR); hepatitis A; and meningococcal disease.

According to the report, evidence "convincingly supports a causal relationship" for only 14 specific adverse effects, including a range of infections associated with the chickenpox vaccine; brain inflammation and fever-induced seizures related to the MMR vaccine; allergic reactions to six of the vaccines and fainting or local inflammation caused by injection of any of them. The report noted that many of the more serious events, such as those linked to the chickenpox and MMR vaccines, only occur in children with weakened immune systems.

The report also includes less-convincing evidence of links between four other adverse events and particular vaccines.

On 135 other possible links between the vaccines and adverse effects, the panel concluded that there was "inadequate evidence to accept or reject a casual relationship".

The VICP could use this information to update its Vaccine Injury Table, which already includes most, but not all, of the adverse effects listed in the IOM report.

Dispelling controversy
The committee found that evidence "favors rejection" of discredited reports that have linked the MMR vaccine to autism and, along with the DTaP vaccine, to type 1 diabetes.

"We found five really solid epidemiological reports that were very clear that MMR is not associated with autism, and does not cause autism," Wright Clayton says.

Previous IOM reports have reached the same conclusion, and a 1998 paper by Andrew Wakefield — a UK surgeon who has now been struck off the medical register — that posited a link between vaccines and autism was retracted last year by The Lancet . The journal noted that "several elements" of the original paper were "incorrect". But some parents who still believe there is a connection refuse or delay vaccinations for their children, leading to outbreaks of diseases such as measles and whooping cough.

"For those parents who are on the fence, this will be another piece of reassuring evidence, although I don't know how many more pieces of reassuring evidence you need," says Paul Offit, chief of the infectious diseases division of The Children's Hospital of Philadelphia in Pennsylvania. "For those who are committed to the concept that vaccines are harmful independent of what the data say, it won't matter."

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.