Abstract
Despite the spectacular success of vaccines in preventing infectious diseases, fears about their safety and other anti-vaccination claims are widespread. To better understand how such fears and claims persist and spread, we must understand how they are perceived and recalled. One influence on the perception and recall of vaccination-related information might be universal cognitive biases acting against vaccination. An omission bias describes the tendency to perceive as worse, and recall better, bad outcomes resulting from commissions (e.g. vaccine side effects) compared to the same bad outcomes resulting from omissions (e.g. symptoms of vaccine preventable diseases). Another factor influencing the perception and recall of vaccination-related information might be people's attitudes towards vaccines. A confirmation bias would mean that pre-existing pro-vaccination attitudes positively predict perceptions of severity and recall of symptoms of vaccine preventable diseases and negatively predict perceptions of severity and recall of vaccine side effects. To test for these hypothesized biases, 202 female participants aged 18-60 (M = 38.15, SD = 10.37) completed an online experiment with a between-subjects experimental design. Participants imagined that they had a 1-year old child who suffered from either vaccine side effects (Commission Condition) or symptoms of a vaccine-preventable disease (Omission Condition). They then rated a list of symptoms/side effects for their perceived severity on a 7-point Likert scale. Finally, they completed a surprise recall test in which they recalled the symptoms/side effects previously rated. An additional scale was used to measure their attitudes towards vaccines. Contrary to the hypotheses, perceptions of severity and the recall of symptoms/side effects were not associated with experimental condition, failing to support the omission bias, nor did they interact with attitudes towards vaccines, failing to support the confirmation bias. This cast doubt on the possibility that the spread of anti-vaccination claims can be explained by these particular universal cognitive biases.
Highlights
Ever since vaccination was developed in the late 18th century, it has been accompanied by scepticism and opposition
Statistical analyses were preregistered on the Open Science Framework (OSF) website
We found no evidence to support the omission bias hypothesis in either severity ratings (H1a) or recall (H2a) of vaccine-related symptoms and side-effects
Summary
Ever since vaccination was developed in the late 18th century, it has been accompanied by scepticism and opposition. Smallpox vaccination entailed the introduction of an alien substance into the human bloodstream, which was seen as a violation of bodily purity and as the cause of, rather than the cure for, diseases [3]. Smallpox vaccination involved the mixture of a substance coming from a cow with human blood, which was considered anti-natural and anti-Christian in Europe [2] and was disturbing for Hindus in colonial India [1]. Anti-vaccination messages recurrently emerge and spread through the mass media [7, 8], social media [9] and on anti-vaccination websites [10,11,12,13,14]. As a consequence of the erosion of herd immunity and the formation of clusters of unvaccinated individuals [17], outbreaks of vaccine-preventable infectious diseases still occur in developed countries, sometimes leading to fatal consequences
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