More than any other information source, a parent's social network influences the decision to follow governmental guidelines for childhood vaccines, a small study suggests.

Researchers surveyed 196 parents in King County, WA, which along with parts of Vermont, Wisconsin and Minnesota has been affected by a pertussis outbreak, the result of a higher rate of parental resistance to childhood vaccines. Whether or not they chose to vaccinate their young child, 95 percent of parents said they consulted friends and families for opinions, while only a small fraction relied solely on recommendations from the U.S. Centers for Disease Control and Prevention.

Researcher Emily Brunson, an assistant professor of anthropology at Texas State University in San Marcos, said the study leaves open the question of whether parents make decisions based on the influence of their personal networks. "It's a chicken-and-egg question," she said. "The answer is: we don't know which came first."

In the study, 126 parents followed the government childhood-vaccine schedule for their children, 18 months of age or younger, while 28 delayed vaccines and 37 chose to vaccinate for some diseases but not others. Five parents in the study chose not to vaccinate their children at all.

Approximately one in ten parents in both groups, those who followed guidelines and those who did not, failed to cite their pediatricians as among the top five people influencing their decision. Among parents who chose not to vaccinate their children, 72 percent said their friends and families advised them to disregard government advice, suggesting a social marketing target for public health officials.

According to the research, parents who chose to disregard vaccine guidelines were also more likely to possess "source networks," turning to books, websites and magazines for information. Many turned to information sources promulgating an association between childhood vaccines and autism, which science has since widely debunked.

In the age of social media, parents and support networks often blame childhood vaccines for unexplained deaths and rare diseases, distrusting America's most profitable industry — "big pharma," with more than twice as many lobbyists in Washington than congressmen.

Local Facebook networks erupted last year, for example, when Kaylynne Matten, a 7-year-old of Barton, VT, died after receiving the influenza vaccine. Dr. Harry Chen, state health commissioner, subsequently ruled the death unexplainable but not attributable to the vaccine, listing as a contributing factor myocarditis, a rare inflammation of the heart usual by a virus. "In my opinion I don't think [the vaccine] had anything to do with it," he said, "but I don't have the evidence to be absolutely certain to say no."

Such bits of anecdotal evidence from rare, and heart-rending, occurrences reverberate throughout online and interpersonal networks alike.

However, some vaccine skeptics conduct more in-depth research when making decisions about childhood vaccinations. Barbara Cerf, a former research scientist and mother based in San Diego, told Medical Daily she disregards government advice — choosing some of the vaccinations but not all.

"I personally research in stages, generally starting with a global Google search, which often leads to forums, wiki entries and magazine articles," she said. "This gives me keywords that I use for more thorough searches in 'Pubmed' and on [National Institutes of Health] websites and National Center for Complementary and Alternative Medicine.

Cerf said she reads a few articles in entirety and then screens many more others, searching for affiliations and disclaimers. "I also check international sources and mostly European ones — they give a different perspective, which is often very useful on topics related to FDA regulated issues.

"Don't forget that a lot of people out there do their searches right," Cerf said. However, not every parent of young children works as a scientific grant writer.

The research appeared Monday in the online version of the May issue of the journal Pediatrics.