Supplementary Material for: How Social Exclusion, Embitterment, and Conspiracy Beliefs Mediate Individual’s Intention to Vaccination against COVID-19: Results from a Moderated Serial Mediation Analysis

<b><i>Introduction:</i></b> As Switzerland faced the “second wave” of COVID-19 incidences, a discussion of a potential vaccine against the virus emerged. While some individuals accept vaccines, others challenge or refuse to be vaccinated, a phenomena called <i>vaccine hesitancy</i>. Here, trust plays a vital role in vaccination intention. Embitterment not only goes along with the sense of being treated unjust but also innates a distrust in others. Thus, embitterment may influence individuals’ vaccination intention against COVID-19. In the present study, we investigate how feelings of being socially excluded and the perceived negative impact of the pandemic are associated with embitterment and in turn, how embitterment is related to individuals’ vaccination intention and the tendency to hold COVID-19-related conspiracy beliefs (CCBs). This is in regard of the perceived communication style by the government. <b><i>Method:</i></b> A convenience sample of 281 individuals completed an online survey developed on Qualtrics. In this cross-sectional, nonexperimental designed study, indirect effects of a moderated serial mediation were analyzed using <i>Jamm</i> (Jamovi, Version 0.9; 2019). <b><i>Results:</i></b> Results indicated that embitterment went along with increased feelings of social exclusion (β = 0.45, <i>p</i> &lt; 0.001). Further, individuals high in embitterment generally indicated a higher vaccination intention against COVID-19 (β = 0.15, <i>p</i> &lt; 0.01). However, embittered individuals holding CCBs had a decreased vaccination intention against COVID-19 (β = −0.71, <i>p</i> &lt; 0.001). Thus, whether or not embittered individuals develop CCBs might be a crucial determinant for their vaccination intention. Noteworthy, the relationship between embitterment and the tendency to hold CCBs was reinforced by the notion of an unsatisfactory style of communication by the government. <b><i>Conclusion:</i></b> Taken together, results suggest that embitterment not only plays a relevant role in vaccination intention against COVID-19 but also for the susceptibility to engage in conspiracy beliefs.