Vaccines are one of the most effective global public health interventions. From a psychological perspective, we can view the individual decision to vaccinate as a classic social dilemma: if everyone cooperates we will all be better off but it only takes a small group of defectors to quickly ruin it for everyone. If enough individuals in a given population agree to get vaccinated, communities can protect themselves against potentially life-threatening diseases. For example, the smallpox virus was one of the world's most devastating diseases. Thanks to a global immunization campaign coordinated by the World Health Organization, the disease was officially eradicated in 1980.
Yet, when a small number of individuals decide to go against the societal norm to vaccinate, they (inadvertently) put entire communities at risk. This is so because unvaccinated people tend to cluster together geographically, which allows a virus to spread and take hold quickly. Fortunately, small outbreaks can often be controlled. What is concerning, however, is that such outbreaks are becoming more frequent. For example, the United States logged a record number of measles outbreaks in 2014. It is one thing for people to decide that they are willing to put themselves at risk, it is another to put other communities or even the entire population at risk. The resurgence of measles in the United States has been attributed to the impact of so-called "vaccine deniers". To what extent should individual liberties come at the cost of others' well-being?
Given the seriousness of the potential public health risks at stake, the psychological study of why some people decide not to vaccinate is receiving increased attention. It seems unlikely that people use religious, philosophical, or political motives to justify a concerted initiative to willingly put their fellow citizens and children at risk. We accept small risks everyday, from letting our children play outside to riding the bus. Of course, sometimes, the influence of extreme ideologies (particularly in disenfranchised communities) can trump the influence of other societal norms. For the majority, however, vaccine hesitancy is often motivated by influential misperceptions about vaccine risks. Indeed, popular examples of misguided notions about how vaccines and the human immune system work range from the idea that vaccines cause autism and that one can catch the actual flu from the flu vaccine to conspiracy theories about "big pharma", government "mind-control" initiatives and a "Western plot" to infect non-Western communities.
Some of these misperceptions can be influential and far-reaching. For example, about 50% of Americans indicate that they are "unsure" about whether or not vaccines cause autism. General concerns about childhood vaccine safety have increased over the last decade as well. Although immunization rates are currently high in the United States, it is a slippery slope when people start acting on such misinformation. For example, doctors now frequently receive requests to "delay" childhood vaccines. This trend is also evidenced by the astonishing backlash against Mark Zuckerberg's recent decision to vaccinate his baby. A functioning democracy requires that the public is well-informed. "If a majority believes in something that is factually incorrect, the misinformation may form the basis for decisions that run counter to a society’s best interest" (Lewandowsky et al., 2011).
Research has shown that it proves incredibly difficult to effectively communicate with the public about vaccine safety. A recent article in the Washington Post suggests that people should stop calling anti-vaxxers "dumb" - this seems to be a rather mundane conclusion, clearly nobody likes to be called dumb! On the other hand, so-called "meta-reviews" of pro-vaccine communication strategies are often inconclusive about their general effectiveness. In fact, some studies have shown that attempts to correct misperceptions can actually backfire and make people less likely to vaccinate.
Two major issues complicate these efforts:
1) First is the so-called "false media balance". Journalists often follow a professional norm to present (anecdotal) examples about a topic in a seemingly "balanced" pro-and-con fashion. Research by some of my colleagues has shown that such media impressions actually fail to emphasize the overwhelming amount of scientific agreement on vaccine safety, which, in turn, strongly influences how people think about the issue.
2) The other major issue is that much (if not most) of our communication efforts are directed at trying to correct misinformation "myths" with the expectation that people will rationally respond to such a correction. However, research in cognitive psychology has taught us that when we are trying to debunk a myth (e.g., that a long time ago, one fraudulent study incorrectly concluded that vaccines cause autism) the memory networks associated with the misinformation are activated and strengthened. Because it takes more cognitive effort for people to update their beliefs in light of new information, such strategies often just end up reinforcing the myth.
In a new study published in BMC Public Health, my colleagues and I set out to test a different approach: highlighting the level of normative agreement -or consensus- among medical scientists about vaccine safety. The benefit of communicating the extent to which medical experts agree about the safety of vaccines speaks directly to the points above: we correct the false media balance by highlighting the high degree of consensus AND, at the same time, we avoid having to repeat any type of "misinformation".
Consensus information tells us how many experts, friends, or other people we care about agree on a particular issue of importance. We deal with consensus information all the time in daily life, from consensus on what restaurant dish is the most popular to consensus among critics about the quality of a particular movie. People are naturally inclined to pay attention to consensus because consensus cues often signal important information. For instance, think about the restaurant example. There is a good reason why a particular dish is the most "popular", it has some quality that leads most people to enjoy it. In a complex and uncertain world, where we have limited time to decide on a particular course of action, we often have to make strategic "bets" on what decision is going to be the right one. Human reliance on consensus heuristics evolved because they are adaptive for survival. In fact, some recent neuroscientific studies actually show that people experience a feeling of pleasure and reward when they learn that their opinions are in line with the (expert) consensus. There is a good reason for this positive association. For example, if 9 out of 10 doctors tell you that you need surgery right away, simply relying on the expert consensus will most likely be in the best interest of your health. Some of my colleagues refer to this notion as the "simple heuristics that make us smart".
In our study, participants read one of the following treatment messages; "90% of medical scientists agree that vaccines are safe", "90% of medical scientists agree that parents should be required to vaccinate their children" or a combination of both. In the control group, no information was provided (90% is actually a very conservative estimate of expert consensus based on national surveys among doctors and medical scientists). In short, we found that after exposure, people (conservatives and liberals alike) were not only substantially more likely to understand that there is a strong consensus among medical experts about vaccine safety, participants were also less likely to think that vaccines cause autism or that childhood vaccines are risky, and more likely to vaccinate their children and support policies that require parents to vaccinate their children.
We generally find that people's perception of the level of consensus among domain experts [medical scientists] functions as a "gateway" to changing other influential beliefs that people hold with regard to important societal issues. In other words, communicating consensus has the potential to correct influential misperceptions while cultivating science-based attitudes toward and public support for vaccinations.
I have written about the psychology of consensus before. Of course, I am not suggesting that there is no need or place for people to learn exactly why vaccines do not cause autism or why you cannot catch the flu from a flu shot. The truth is that people care more about certain type of facts than about others and facts with social value (e.g., group consensus) tend to carry more weight. In an uncertain and complex world where people have limited time and attention, communicating the bottom-line is often what counts the most. In this case, that 90% of doctors all agree that approved vaccines are perfectly safe and that it is important for your health that you get yourself and your children vaccinated.
Center for Disease Control (CDC) Global Health - Vaccines and Immunization. Available from: http://www.cdc.gov/globalhealth/immunization/
Gellin, B.G., Maibach, E.W., & Marcuse, E.K. (2000). Do parents understand immunizations? A national telephone survey. Pediatrics, 106(5), 1097–1102.
Gust, D., Weber, D., Weintraub, E., Kennedy, A., Soud, F., & Burns, A. (2008). Physicians who do and do not recommend children get all vaccinations. Journal of Health Communication,13(6), 573–582.
Dubé, E., Gagnon, D., & MacDonald, N.E. (2015). Strategies intended to address vaccine hesitancy: Review of published reviews. Vaccine, 33(34), 4191–4203.
Dixon, G., & Clarke, C. (2013). The effect of falsely balanced reporting of the autism-vaccine controversy on vaccine safety perceptions and behavioral intentions. Health Education Research, 28(2), 352-359.
Lewandowsky, S., Ecker, U.K.H., Seifert, C.M., Schwartz, N., & Cook, J. (2012). Misinformation and its correction: continued influence and successful debiasing. Psychological Science in the Public Interest, 13(3),106–131.
Maibach, E. (2012). Knowing our options for setting the record straight, when doing so is particularly important. Psychological Science in the Public Interest, 13(3),105.
van der Linden S.L., Leiserowitz, A.A., Feinberg, G.D., Maibach, E.W. (2012). The scientific consensus on climate change as a gateway belief: Experimental evidence. PLoS One 10(2), e0118489.
van der Linden, S.L., Clarke, C.E., & Maibach, E.W. (2015). Highlighting consensus among medical scientists increases public support for vaccines: Evidence from a randomized experiment. BMC Public Health, 15(1), 1207.