An analysis of nearly 500 anti-vaccination websites found that over two-thirds used what they represented as scientific evidence to support the idea that vaccines are dangerous and nearly one-third contained anecdotes that reinforced the perception.

As is the case among other anti-science movements, like those related to energy and agriculture, the sites contained a considerable amount of misinformation and pseudoscience, with more than two-thirds suggesting that vaccines were dangerous, just under two-thirds suggesting they cause autism and just over 4 in 10 claiming vaccines cause "brain injury."

More than two-thirds selected "scientific" evidence that in fact was not, while about 3 in 10 used anecdotes as evidence. Many sites also promoted unrelated behaviors as being medically relevant to not getting a disease like polio, such as eating better (18.5 percent), eating organic (5.2 percent) and breastfeeding (5.5 percent).

The scholars looked at sites with content about childhood vaccines but did not break out their analysis by individual vaccine. They searched four search engines - Google, Bing, Yahoo and Ask Jeeves - using terms like "immunization dangers" and "vaccine danger" and others were identified using Google Trends. After eliminating duplicates, they had a mix of personal websites and blogs, Facebook pages and health websites. A team of four coders labeled the content for the vaccine misinformation presented, the source of the vaccine misinformation and the types of persuasive tactics used. The coders also coded for behaviors and values co-promoted by the websites that could help vaccine promotion efforts develop better-targeted materials.

"The biggest global takeaway is that we need to communicate to the vaccine-hesitant parent in a way that resonates with them and is sensitive to their concerns," says Meghan Moran, PhD, associate professor in the Bloomberg School's Department of Health, Behavior and Society and lead author of the study. "In our review, we saw communication for things we consider healthy, such as breastfeeding, eating organic, the types of behavior public health officials want to encourage. I think we can leverage these good things and reframe our communication in a way that makes sense to those parents resisting vaccines for their children."

"Why are anti-vaccine messages so persuasive? A content analysis of anti-vaccine websites to inform the development of vaccine promotion strategies" was presented at the American Public Health Association's Annual Meeting in Chicago on Nov. 3.