America prefers to get its vital facts about vaccines from anonymous website commenters over the CDC. Alamy

As the vaccination wars continue to escalate, a new study suggests that trusted doctors and experts may be no match for the loud and often inaccurate wisdom of Internet commenters.

In a first-of-its kind experiment, researchers at Washington State University have shown that people tend to be persuaded less by credible pro- and anti-vaccination information published online than by individual users who hang around in comments threads on the topic kicking up dust.

The findings, which will appear in an upcoming Journal of Advertising, underscore the powerful influence of information disseminated by word of mouth. Moreover, they offer a striking insight into the ability of the anti-vaccination movement to flourish despite mounting outrage and overwhelming scientific evidence that supports vaccination.

For the study, “Reexamining Health Messages in the Digital Age: A Fresh Look at Source Credibility Effects,” researchers conducted a pair of experiments with 129 participants. In the first experiment, the study’s subjects were shown two mock public service announcements, one that purported to be a pro-vaccination message sponsored by the Centers for Disease Control and Prevention and the other an anti-vaccination message from the National Vaccine Information Center. They were then shown a series of fictitious online comments that appeared to be in response to the official messages. The participants were given no information at all about the commenters.

After reviewing the PSAs and comments, the participants completed a questionnaire about their opinions on vaccination. To their surprise, the researchers found that the participants were as persuaded by the commenters as they were by the PSAs, even though they had no knowledge of commenters’ background or expertise.

“That kind of blew us away,” says Ioannis Kareklas, the study’s lead author. “People were trusting the random online commenters just as much as the PSA itself.”

In the second experiment, participants were told that the fictitious commenters were a student of literature, a health care lobbyist and a doctor who specialized in infectious diseases. This time, participants were more persuaded by the bogus doctor than the PSAs, even though nothing about the physician or his claims could be verified.

A copy of the study can be downloaded here.