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Krystal Lau, Imperial College LondonAbstract: ‘Nudge’-based social norm messages that signal uptake strength of a certain behaviour within a population can be used in public health interventions to shape individuals’ decisions to adopt that behaviour. Messages conveying high influenza vaccination coverage levels signal a strong social norm, encouraging vaccination, but also a low risk of infection, discouraging vaccination and promoting free-riding. The complex interplay between these two signals can result in ambiguous vaccination decision-making behaviour, especially as coverage levels vary. We aimed to measure different vaccination coverage levels’ impact on influenza vaccination intention.

In an online experiment, we randomly assigned 1,365 UK residents aged 18+ years to a control group (with no message) or one of seven treatment groups with different messages of vaccination coverage levels, shown as the proportion of vaccinated people (10%, 25%, 50%, 65%, 75%, 85%, or 95%) in the respondents’ environment. Impact on respondents’ vaccination intention was measured using self-reported intention and three elicited behaviour measures: (a) opening an online map locating nearby private flu jab providers; (b) time looking at this map; and (c) downloading a calendar reminder to vaccinate.

Treatment groups had significantly higher stated and elicited vaccination intention than the control. Below the 75% to 85% threshold, groups treated with higher coverage levels had greater vaccination intention than groups treated with lower levels. Groups treated with coverage levels above this threshold, compared to those below, had lower vaccination intention. Policymakers should consider this curvilinear effect when designing interventions that use social norm messages to ‘nudge’ vaccination.

Biography: Krystal’s research primarily focuses on behavioural economics. Specifically, she investigates the impact of social norms on vaccination decision-making. She also works on identifying and characterizing key players in the anti-vaccination movement on social media. She has a broader interest in infectious diseases and pandemics, transmission of information and beliefs, and social network analysis. Krystal holds an MRes from Imperial College Business School as well as an MSc in Bioscience and Health Policy, a Bachelor's of Science in Biochemistry and Cell Biology, and a Bachelor's of Science in Health Care Management Policy Studies from Rice University in Houston, Texas.