Children holding hands

Photograph by Spencer Wright

The power of social ties may be stronger than you think.

Who’d think that social networks would have anything to do with a deadly disease outbreak in Wales? But studies now suggest that these networks–in real life and online–can powerfully influence decisions parents make about vaccinating their children.

It’s a tragic irony that the United Kingdom is in the throes of one of the worst measles epidemics in decades just as the United Nations World Immunization Week is upon us. Over 1,000 cases of the highly contagious and potentially fatal disease have been reported in Wales and in northeast England. Yet measles is preventable with the measles-mumps-rubella (MMR) vaccine – as long as enough people are vaccinated.

Alas, thanks to an infamous and thoroughly debunked case series study by a fraudster over a decade ago, MMR immunization rates have lagged in the UK, and public health efforts to reassure folks of the safety and effectiveness of the vaccine just haven’t been hitting home for enough people. A couple of recent studies, including one last week from Pediatrics, shed some light on what officials in the US and possibly the UK are up against.

The short answer: peer pressure. And peer pressure is powerful.

The Pediatrics study, conducted by medical anthropologist Emily Brunson at Texas State University, found that parent social networks, both in real life or online, play a significant role in decisions parents make about vaccinating their children. This finding may not sound groundbreaking, but it is disturbing when you consider that many parents are making a vitally important personal and public health decision not so much on the basis of what the science says but on the basis of what Aunt June or Kristen in the mom’s group or even Dr. Phil on television says.

After laying the groundwork for her study with some initial research interviewing parents about their vaccination choices, Brunson surveyed 196 parents about these decisions, their perceptions of vaccines and the diseases they protect against, and what sources the parents consulted in drawing their conclusions. The parents all lived in King County, Washington, an area with lower-than-average vaccination rates for the US and the state. Brunson classified them as “conformers” (126 parents) or “nonconformers” (70 parents). The former followed the CDC schedule. The latter either skipped certain vaccines while following the schedule (8 total), delayed certain vaccines but planned to fully vaccinate (28), skipped some vaccines and delayed the rest (29 total), or didn’t vaccinate altogether (5 total).

When she asked the parents about the most influential people and sources they consulted for their vaccination decisions, Brunson found a couple of trends. First, 59% of the people in nonconformers’ “source networks” recommended “something other than complete, on-time vaccination.” But only 20% of the conformers’ source networks suggested anything other the CDC schedule. In other words, regardless of whether they vaccinated their kids partially, fully, delayed, or on time, they were basically choosing what their friends and family were recommending.

These findings match what social psychologists have found in other contexts, says Melanie Tannenbaum, a social psychology PhD student at the University of Illinois at Urbana-Champaign. “We’re incredibly susceptible to the power of descriptive norms,” Tannenbaum says. “Simply knowing that other people do or think something can be a much more powerful force than being told what should do or think.”

But Brunson also found that nonconformers listed more people that they had consulted for their decision (an average 6.7 people, compared to 4.8 among conformers) and more non-people sources (4.4 on average, compared to 3.4 among conformers). Also, 39% of nonconformers said they had actively sought out the non-people sources, compared to 26% of conformers. So even though parents in both groups appeared influenced by others around them, they differed distinctly in how they sought information.

“What it implies is that there’s more investigation going on,” Brunson, the study author, says, noting that the parents who aren’t following the CDC schedule are likely looking for more information and talking to more people. But more information doesn’t necessarily add up to the best information.

Interestingly, both groups had similar demographics in terms of household income, age, and education level. Past research has found that parents who don’t vaccinate their children, or who choose a “selective” or “delayed” schedule, tend to have higher incomes and higher education levels. This correlation seems paradoxical at first: Wouldn’t the more highly educated and more well-off parents do what science clearly supports as the best medical choice for their children? Well, one would think, except it’s possible to think you know more than you do, especially in the age of Google University.

“Today, we believe we should know just as much as our doctor by googling terms like vaccines,” says Paul Offit, chief of infectious diseases at Children’s Hospital of Philadelphia, head of CHOP’s vaccine education center, and author of multiple books on vaccines (and the accomplished inventor of the rotavirus vaccine). He says the days of his childhood – when whatever the doctor said went, as if it were the word of God – are gone, and it’s much harder for public health officials to overcome all the competing sources of information. “It’s so much noisier that it’s hard to get your voice heard about the background,” he says.

Brunson thinks her findings tell us that any kind of successful outreach will require public health officials to think big. “The takeaway is that people’s networks are extremely important, so we need to take a step back and take a look at what’s going on in the bigger picture,” she says. “Outreach and interventions need to be broad and accessible to the population generally.”

Aha! I know just the thing that fits that description. There’s this social media networking site called Twitter, and you see …

Well, you see, that’s part of the problem. Only a few weeks before Brunson’s study, another group of researchers published their findings in EPJ Data Science about the spread of vaccination sentiment on Twitter. They designed an algorithm to analyze 318,379 tweets about the H1N1 vaccine as being positive, negative, or neutral. Their three major findings aren’t encouraging:

  • First, negative opinions about the vaccine were contagious, spreading quickly and easily throughout the network, but positive opinions weren’t.
  • Second, negative opinions were also “socially contagious,” which is a little different from the first findings. As one of the authors, Penn State researcher Marcel Salathé, explained in a press release: “When a microblogger had a lot of reciprocal Twitter connections with users who expressed anti-vaccine sentiments, he tended to tweet even more anti-vaccine sentiments himself.” But the opposite did not happen with those tweeting positive sentiments.
  • Third – and worst of all – negative tweets encouraged more negative tweets, and positive tweets encouraged … more negative tweets.

Again, though, much of these findings fit with social psychology research conclusions. “People are not just influenced by their environments; they (the environments) also play a large role in shaping them,” Tannenbaum says. “Research on selective exposure, selective evaluation, and confirmation bias all suggest that people do a remarkably good job of creating their own ‘information bubbles.’”

It’s tough to break people out of their bubbles. Tannenbaum described a meta-analysis in which two researchers found that people are approximately twice as likely to seek out information that supports their existing views than information that challenges it. This behavior is especially true for “value-laden” beliefs, she says – unless the information seeker is motivated primarily by accuracy.

“We would like to think that the health and safety of one’s own children would lead someone to form an accuracy motivation,” Tannenbaum says. “However, attitudes imbued with a lot of ‘moral’ or value-based’ importance tend to make us more defensive of those attitudes.” Therefore, a person seeking information related to an issue with moral undertones is more likely to fall into that “congeniality bias,” seeking confirming information, even if they think they are motivated by accuracy.

Tannenbaum speculates that the influence of moral undertones in immunization decisions may supersede the motivation to find accurate information (probably not consciously) because many of the people who choose not to vaccinate tend to moralize the issue and speak in value-laden terms. “It’s not necessarily about autism, health, or safety as much as it’s about things like ‘individual rights’ or ‘freedom,’ rhetoric that is highly valued in American society,” she says.

Obviously, no explanation or speculation can describe all people who choose not to vaccinate or distinguish them from people who promote vaccination. Many of the latter also moralize the issue because of the very real likelihood that more individuals will die if vaccination rates drop. (In fact, a man died last week in Wales who had measles, though it has not yet been determined whether he died from the measles.) But at the same time, people who vaccinate, as Tannenbaum points out, also adopt a more scientifically based tone that “relies on arguments about epidemics, rates of certain diseases, or potential epidemiological costs.”

Of course, there is more to the story than moralizing and social influences. Tune in tomorrow to read about the fear factor – and what might be done to counteract these different factors.

Written by Tara Haelle


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Double X Science

Double X Science's goal is to bring evidence-based science stories and angles on science specifically of interest to the female-gendered audience.


  1. really terrible ‘measles outbreak’.
    bloody fear-mongering – typical corporate marketing…

    • But that is one completely avoidable death, with the MMR vaccine free on the NHS. The symptoms of measles are also pretty miserable, and again completely avoidable.

      Why would we not vaccinate against something so contagious?