One of the aims of the CCP Vaccine Risk Perception and Ad Hoc Risk Communication study was to examine the impact of empirically uninformed vaccine risk communication.
By “empirically uniformed risk communication,” I don’t mean vaccine-risk misinformation, such as the claim that childhood vaccines cause autism. I take as a given that false assertions like that generate unwarranted public concern.
Rather, I’m using “empirically uniformed risk communication” to denote information that accurately conveys the risks of childhood vaccines--likely for the very appropriate purpose of counteracting misinformation-- but that nevertheless embeds that information in empirically insupportable representations about the extent, sources, and consequences of public unease toward universal immunization.
Disseminated by journalists, advocates, and even some public health professionals, this kind of vaccine-risk communication is the type that ordinary members of the public are in fact most likely to be exposed to.
It’s core message is that public health in the U.S. is being threatened by a “growing crisis of public confidence” in vaccines. No longer confined to “[t]he fringe who don’t believe in medicine for religious reasons,” a “growing distrust of vaccinations” is now sweeping across “our nation’s parents,” we are told (& told & told & told).
The resulting “erosion in immunization rates” is “predictably ... leading to the resurgence of diseases considered vanquished long ago” including whooping cough and measles. “From Taliban fighters to California soccer moms,” one source concludes, “those who choose not to vaccinate their children against preventable diseases are causing a public health crisis.”
The CCP study didn’t purport to test these claims. Instead, it deferred to sources that employ valid empirical methods specifically suited to measuring immunization rates and the incidence of childhood diseases.
These sources belie the claim that vaccination rates are declining at all, much less “eroding.”
According to data compiled by the U.S. Centers for Disease Control, coverage for recommended childhood immunizations—including MMR, pertussis, Hepatitis-b, and polio—have all been holding steady at or above 90% (the target threshold) for well over a decade (CDC 2013a, 2008, 2006). The proportion of children receiving no vaccinations has persisted at or below 1%, despite the ready availability of nonmedical “exemptions” from state-administered universal immunization policies for objecting parents.
Rather than a “large and growing number” of “otherwise mainstream parents” refusing to vaccinate their children, the CDC reports (in annual press releases, the language of which varies little from year to year) that“ ‘nearly all parents are choosing to have their children protected against dangerous childhood diseases’ ” (CDC 2010)
There are local enclaves, the CDC cautions, in which vaccination rates are significantly lower than the national average. These enclaves are often the site of recurring localized outbreaks of diseases, like measles, which public health officials have deemed eliminated in the United States but which can be introduced into such communities by individuals infected during travel abroad (CDC 2013b).
Fortunately, “[h]igh MMR vaccine coverage in the United States (91% among children aged 19–35 months),” the CDC states, “limits the size of [such] outbreaks,” which averaged 60 cases per year over the last decade (ibid.).
The incidence of whooping cough, which has not been eliminated in the United States, is also likely higher in low-vaccination enclaves (Atwell et al. 2013; Glanz et al. 2013; Omer et al. 2008). But “[p]arents refusing to get their children vaccinated,” according to the CDC, are “not the driving force behind the large scale outbreaks” of this disease in recent years (CDC 2013c). In addition to “increased awareness, improved diagnostic tests, better reporting, [and] more circulation of the bacteria,” the CDC (2013c) has identified “waning immunity “from an ineffective booster shot as one of the principal causes, a view shared by public health experts (Cherry 2012).
Pockets of resistance to vaccination pose a serious and unmistakable public health concern. They merit considered attention informed by empirical methods suited to assessing the influences that generate them, the contributions they make to the incidence of childhood diseases, and the measures that might be employed to counteract and contain them (Opel 2011, 2012; Mnookin 2011; Omer et al. 2008).
But the existence of anti-vaccine enclaves and the dangers they pose do not furnish empirical support for asserting that there is a “growing crisis of public confidence” in childhood vaccines, that “immunization rates with MMR have dropped in . . . the US,” or that a “rising tide of … vaccine reluctance” has generated “a resurgence of diseases gone so long that some doctors don’t even recognize them.”
Such claims reflect not an “epidemic of fear” among ordinary parents, but an epidemic of hyperbole among a diverse collection of actors resorting to ad hoc, empirically uninformed alternatives to genuinely evidence-based forms of risk communication.
I'm sure those engaging in empirically uninformed vaccine risk communication are not doing so in bad faith.
Most probably just don’t know what they are talking about—in part because of the prevalence of empirically uninformed vaccine risk communication.
But some probably do realize that they are in fact grossly mischaracterizing the extent of vaccine avoidance in the U.S., and misattributing to it disease outbreaks that in fact stem from other causes such as the ineffective pertussis booster shot.
They probably figure that this fact-disconnected style of risk communication is okay because it will grab people’s attention and stir them to anger at parents who are not vaccinating their children and definitely should be.
But that way of thinking is empirically uninformed, too. Indeed, the scientific study of science communication suggests that understating the high level of vaccination in the U.S. could actually weaken public support for and cooperation with universal immunization programs.
The “herd immunity” associated with universal childhood vaccination is a collective good (Olson 1965). That is, by complying with universal vaccination policies, parents confer a benefit—reduced risk of contracting a disease—not only on their own children but also on those who as a result of age, medical restrictions, or material disadvantage have not been able to secure the protection that such vaccinations confer.
In collective actions settings—from tax compliance to recycling, from voting to observation of informal norms on picking up one’s children on time from daycare centers—individuals tend to behave like moral and emotional reciprocators (Gintis et al. 2004). That is, rather than engage in purely self-interested calculation, they are motivated to contribute voluntarily to collective goods if they perceive that others are doing so, but to refrain from contributing if they think free-riding is widespread.
This dynamic makes it imperative that people not be induced to underestimate the extent to which others are voluntarily contributing to a collective good. If they do, a higher number of individuals will themselves refrain from contributing—behavior that can be expected to induce others to do the same, generating a self-reinforcing spiral of non-cooperation (Kahan 2004).
The logic of reciprocal cooperation implies that people who believe that others are refraining from getting vaccinated and instead free-riding on the contributions of others to herd immunity will themselves be less willing to get vaccinated. One experimental study using self-report data suggested that students exposed to information that suggested other students were forgoing vaccination and effectively free-riding on the decisions of others to get their flu shots responded in exactly this way (Hershey et al. 1994).
The results of CCP Vaccine Risk Perception study suggest that members of the general public substantially underestimate childhood-vaccine coverage. Asked to estimate “about what percentage of U.S. children (age 19-35 months) received the recommended vaccinations for childhood diseases” in recent years, only 9% of the survey subjects indicated “90% or above”; the median estimate was “70-79%.” In addition, approximately 40% of the sample indicated that the “trend in the rate of vaccination for U.S. children (age 19-35 months)” had gone down either “a little” or “a lot.”
The survey participants likewise grossly overestimated the proportion of children who receive no vaccinations. Only 9% correctly put the figure at “1% or less.” The median response was “2%-10%.” Over one-third of the sample selected either 11% to 20% or 21% to 30%.
Because of the contribution that reciprocity makes to individuals’ motivations to contribute to public goods like herd immunity, this kind of misunderstanding is not good.
Even worse, the experimental component of the CCP study found that individuals’ levels of misunderstanding grew when they were exposed to empirically uninformed vaccine risk communication.
In the experiment, subjects were assigned to one or another condition, members of which read different materials patterned on real-world media and internet sources. Those assigned to the “Crisis” condition read a news that assert “growing” parental resistance to vaccination and a resulting decline in vaccination rates. Those assigned to the “Anti-science” condition read an op-ed commentary that similarly implied that vaccination rates were declining based on fear of vaccine side-effects among individuals disposed to distrust scientific information on issues like evolution and climate change.
Subjects in both the “Crisis” and “Anti-science” conditions underestimated national vaccination coverage. They also were more likely to report that vaccine rates had gone down in recent years.
Subjects in the “CDC” condition, in contrast, received a news story that quoted CDC officials accurately indicating that “vaccination coverage rates . . . have remained stable at or above 90 percent for over a decade,” and that “less than 1% of toddlers had received no vaccines at all,” but also warning of the “the existence of local communities in which vaccination coverage is lower than target levels for certain diseases.”
This communication was patterned on the annual CDC press releases that announce the latest NIS results. Relative to the Crisis, Anti-science, and control group subjects, those in the CDC condition formed much more accurate estimates of the high existing and historical rates of vaccination in the U.S.
Obviously, the high existing rates of vaccination in the U.S. suggest that the degree to which the public currently underestimates vaccination rates is not now inducing widespread noncompliance. But because reciprocity dynamics have been shown to be robust across collective action settings, there is ample reason to discourage journalists, advocates, and health professionals from propagating the misimpression that there is a “growing wave of public resentment and fear” toward vaccines that has resulted in “ ‘erosion in immunization rates’ ”—a refrain, ironically, that strident vaccine opponents gleefully embrace.
Indeed, public awareness that the U.S. has historically enjoyed and continues to enjoy exceptionally high rates of compliance with universal vaccination programs should be regarded as an important public-health resource.
The best available evidence on science and risk communication implies that “public health campaigns that describe the already wide acceptance of pertussis vaccination” and other immunizations against childhood disease is the most reliable way to sustain that widespread acceptance (Hershey et al. 1994, p. 186).
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CDC. CDC Survey Finds Childhood Immunization Rates Remain High. (Sept. 16, 2010), available at http://www.cdc.gov/media/pressrel/2007/r070830.htm.
CDC. National, State, and Local Area Vaccination Coverage Among Children Aged 19– `35 Months — United States, 2012. Morbidity and Mortality Weekly Reports 62, 733-740 (2013a).
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