Abstract
Optimising vaccine uptake is a public health challenge and requires effective strategies. The asymmetric dominance (or decoy) effect describes the increasing likelihood of choosing an alternative when an inferior alternative is offered. Therefore, we aimed to test the impact of offering decoy alternatives, less convenient vaccination appointments, on vaccination intentions. Participants aged 18–33, living in England, who did not intend to get vaccinated, undertook three online experiments. They were randomly assigned to a control or an experimental condition in each experiment. The asymmetrically dominated options were an appointment in two weeks-time at a distant location (experiment 1); at a later time at the participant’s local GP, pharmacy, or community centre (experiment 2); and at a later time at a distant location (experiment 3). Vaccination intention was the primary outcome. Secondary outcomes included an active interest in reading additional information about the vaccination procedure, perceived difficulty and cognitive effort. Initial analysis showed no asymmetric dominance effect. However, further subgroup analysis indicated that ensuring the decoy alternatives are perceived as inferior through formative research could enhance the effectiveness of this approach for some individuals.