Moral Foundations Messaging to Improve Vaccine Attitudes: An Online Randomized Experiment from Argentina

"Vaccine messaging framed as a purity violation is a promising way to improve vaccine attitudes among parents."

The uptake of routine childhood vaccinations has declined globally since the start of the COVID-19 pandemic, due in part to increased vaccine hesitancy among parents. Reaching vaccine-hesitant parents with messages that resonate is no easy task, as fact-based messaging often has been shown to have very little to no effect. For that reason, researchers have turned to Moral Foundations Theory (MFT), which proposes six foundations that can be targeted to increase vaccine uptake: care, fairness, loyalty, authority, liberty, and purity. This study, we tested whether a social media post by the United Nations Children's Fund (UNICEF) with a purity violation message could affect vaccine attitudes among parents in Argentina, where routine immunisation (RI) coverage has been declining since 2014.

Between July 1-12 2022, the researchers conducted an online randomised controlled survey of 1,511 parents with a child under 12 years in Argentina. A total of 111 parents (7% of the sample) was categorised as undervaccinating their children, which included not vaccinating their children at all, as well as delayed and partial vaccination.

One way to tap into the purity value (as per MFT) is by appealing to disgust. The text of the intervention post therefore read (in Spanish): "It is important to vaccinate your children following the schedule to keep them free from disgusting diseases like polio and measles". The message was vetted by the UNICEF country office in Argentina, keeping in mind cultural sensitivities. After reading the post, the intervention group (n=756) answered the questions of the main outcome measure: the Vaccine Trust Indicator (VTI). As a non-vaccine-specific scale, the VTI has been developed to measure vaccine confidence among the general population.

The study found that the purity violation message significantly affected vaccine attitudes: 80% of the intervention group scored high on the VTI, compared to 73% in the control group (coefficient: 0.33, 95% confidence interval (CI) 0.20-0.47). 

This study was not powered to detect an effect among parents of undervaccinated children; future research could test various moral messaging strategies on different hesitancy profiles.

Reflecting on the findings, the researchers note: "Taken together, pro-vaccination messages with a focus on purity violations could be used to enhance vaccine trust, attitudes and intentions....Developing these messages should be done with great care, be informed by behavioral insights and targeted towards the key audience of the messages....The...message on 'disgusting diseases' should also be used with great care, as unintentional stigmatization of people who have contracted measles or polio should be avoided."

In conclusion, the study "has promising implications for future message framing for health agencies charged with strengthening childhood vaccination coverage."