Confirmation bias and vaccine-related beliefs in the time of COVID-19

Background In recent history mass vaccination has proved essential to dealing with pandemics. However, the effectiveness of a vaccine depends on the number of people willing to take it. One approach to encouraging uptake is to publish information about safety and effectiveness. But confirmation bias research in other domains suggests that people may evaluate this information through the lens of their existing beliefs. Methods This study used a simple 2 x 2 design to investigate whether people's (n = 3899) existing beliefs influenced their ability to correctly evaluate data from a fictional trial presented in a frequency table. Treatment groups saw different trial outcomes (intervention effective versus ineffective and trial related versus unrelated to vaccines). Results Results provided robust evidence for confirmation bias in the domain of vaccines: people made systematic errors (P < 0.01) when evaluating evidence that was inconsistent with their prior beliefs. This pattern emerged among people with both pro-vaccination and anti-vaccination attitudes. Errors were attributed to confirmation bias because no such differences were detected when participants evaluated data unrelated to vaccines. Conclusions People are prone to misinterpreting evidence about vaccines in ways that reflect their underlying beliefs. Confirmation bias is an important consideration for vaccine communication.