Understanding Parental Vaccine Refusal: Implicit and Explicit Associations about Vaccines as Potential Building Blocks of Vaccine Beliefs and Behavior

"...vaccine associations - especially those related to helpfulness/harmfulness - may serve as psychological building blocks for parental vaccine beliefs and behaviors."

A movement of parents refusing vaccines for their children has contributed to increasingly large outbreaks of vaccine-preventable diseases (VPDs) in countries such as the United States (US). Research has identified multiple factors that relate to parents' vaccination behaviours (i.e., whether not they vaccinate their children), including their beliefs about vaccines' safety and utility and their trust in those who recommend vaccines. This article examines the role of more fundamental psychological processes that may contribute to multiple vaccine-related beliefs and behaviours: cognitive associations. Specifically, it shares research examining the role of linking of concepts or stimuli in memory in vaccine-related beliefs and behaviours.

As explained here, the cognitive process of association happens automatically: People have positive or negative evaluations of a "target" (e.g., a negative evaluation of vaccines) that come from existing direct or indirect experience with the target or similar targets, and these feelings are strongest for regularly encountered targets. For instance, reading online testimonies linking measles, mumps, and rubella (MMR) vaccines to autism spectrum disorders may create automatically active negative reactions to vaccines based on an association between vaccines and harm. (This claim about MMR vaccines, initially established by a later-retracted article published by Andrew Wakefifled in 1998, has gained traction by the anti-vaccination movement, despite the finding that it is false.) From there, people translate their initial feeling into a proposition: a statement of fact about their evaluations (e.g., "I dislike MMR vaccines"). Finally, they validate the proposition by examining whether it is consistent with other relevant and activated propositions (e.g., thoughts about other vaccines, such as the flu shot).

Notably, even if people have negative associations with vaccines, they might not openly endorse those beliefs to avoid social embarrassment. Researchers call the associations that people are willing and able to self-report "explicit associations". By contrast, they call the associations that people are either unwilling or unable to report or cannot control (e.g., because they are automatic or unconscious) "implicit associations".

Participants in the study were 863 US parents who completed measures of implicit and explicit associations (primary predictors), attitudes toward vaccines and trust in authorities who recommend vaccines (mediators), and prior vaccine refusal (outcome), in addition to basic demographic questions. The researchers investigated parents' associations between vaccines and helpfulness/harmfulness, as well as between the self and vaccines (vaccine identity), and their relation to parents' beliefs about vaccine safety and utility, trust in authorities' vaccine recommendations, and prior vaccination refusal for their children. The data were collected during the 2014 and 2015 measles outbreak in the US that preceded the record-breaking measles outbreak of 2019.

Consistent with the general rarity of vaccine refusal in the population, a minority of participants (n = 74; 11% of those responding to the question) indicated they had refused a vaccine for their child at some point. However, 68.3% of participants endorsed at least one anti-vaccination belief, indicating at least some vaccine hesitancy, and half of those parents endorsed two or more anti-vaccination beliefs. ("This finding further highlights the need to examine and identify fundamental cognitive processes that might underlie multiple different anti-vaccination beliefs.")

As expected, implicit and explicit associations were associated with higher pro-vaccine beliefs, greater trust in authority recommendations, and lower likelihood of past vaccine refusal. Consistent with previous findings, people more strongly endorsed pro-vaccine beliefs to the extent that they were politically liberal, educated, older, and less religious. Men also endorsed pro-vaccine beliefs more strongly than did women. People trusted authority recommendations regarding vaccinations more to the extent that they were politically liberal, educated, and older.

Implicit and explicit vaccine-helpfulness associations and vaccine identity related to greater pro-vaccine beliefs, greater trust in authorities' vaccine recommendations, and lower likelihood of past vaccine refusal. In a structural equation model, stronger implicit and explicit vaccine-helpfulness associations and stronger explicit self-vaccine associations related independently to greater endorsement of pro-vaccine beliefs and more trust in authority recommendations. Those associations were also related to lower likelihood of prior vaccine refusal indirectly, via pro-vaccine beliefs, even after controlling for demographics.

In addition, explicit - but not implicit - vaccine-helpfulness related to lower likelihood of prior vaccine refusal indirectly via trust in authority recommendations even after controlling for demographics. Implicit associations were most important for those who did not self-report strongly associating vaccines with helpfulness. Implicit vaccine identity only mattered for those who self-reported high vaccine identity. These findings suggest that associations between vaccines and helpfulness and, to a lesser extent, associations between vaccines and the self, might serve as fundamental building blocks for anti-vaccination beliefs and behaviours. Nevertheless, the relationship appears to be nuanced in predicting beliefs: Implicit attitudes matter most for those who explicitly identify with vaccines and those who associate vaccines with harmfulness.

One implication of this study is that understanding the anti-vaccination movement may require more than asking people to report on their thoughts and associations about vaccination directly. Researchers should consider employing indirect measurement approaches as a companion to direct measurement approaches and consider the interaction between the attitudes captured by these two types of measures. Longitudinal research could examine the effects of societal and policy changes related to vaccines on personal- and societal-level changes in implicit and explicit vaccine associations.

The findings also suggest that interventionists wishing to reduce anti-vaccination beliefs and behaviour may consider targeting implicit helpfulness/harmfulness associations. A possible reason that earlier interventions did not work is that they did not consider implicit processes - that is, the idea that people may be unwilling or unable to report a gut sense that vaccines are harmful. Although implicit associations can be difficult to change, interventionists could consider working at three possible levels to improve vaccine uptake:

1. Change the situation in which decisions are made via policy. For instance, reducing exemptions to vaccine requirements for school entry can increase vaccine uptake, regardless of parents' beliefs.
2. Work on disrupting associations by reducing exposure to false information (e.g., by shutting down anti-vaccination social media groups that communicate false scientific information) and increasing exposure to more accurate scientific information.
3. Make people aware of their implicit vaccine-harmfulness associations, particularly if they explicitly endorse pro-vaccine beliefs, which can allow greater control over their own behaviour and lessen the influence of implicit beliefs.

In conclusion: "Although further investigation in a larger and more socio-demographically diverse longitudinal sample will provide a richer picture of the role of implicit attitudes in vaccine beliefs and behavior, ultimately, the present findings suggest the utility of considering basic cognitive processes when seeking to understand the anti-vaccination movement and resultant vaccine-preventable disease outbreaks."