Mistrust, uncertainty, fear, and vaccine acceptability: quasi-experimental data from the United Kingdom and Portugal during the COVID-19 pandemic

Using a quasi-experimental design, this study tests a cognitive-affective model of vaccine acceptability focusing on the effects of relationships between trust, certainty, attitudes, and fear in a sample of 1132 adults in the UK (N = 648 [51.7%]) and Portugal (N = 486 [48.3%]) during the COVID-19 pandemic. A path model of the relationships between the variables was assessed using structural equation modeling. Participants in the experimental condition were asked to list what they thought were the major societal uncertainties concerning the COVID-19 vaccines (N = 566 [49.9%]). When subsequently asked, those in the experimental condition reported lower vaccine certainty than those in the control condition (N = 568 [50.1%]). Across the entire sample, lower vaccine certainty was associated with lower vaccine acceptability. Higher vaccine uncertainty was associated with less negativity toward vaccine refusers (which in turn was associated with lower vaccine acceptability). In addition to the direct positive effect of trust in science and scientists upon vaccine acceptability, there were mediated effects: higher trust in science and scientists was associated with higher fear. Fear was positively associated with vaccine certainty. Fear was also positively associated with negativity toward vaccine refusers. The results suggest that, in health crises, people may be more susceptible to identify with other vaccine refusers (and potentially ‘anti-vaxxer’ groups) if levels of uncertainty and mistrust are higher, thereby undermining vaccine uptake. The study makes an original contribution to the literature on vaccine acceptability by showing that vaccine certainty (and changes in vaccine acceptability) can be modified by a single intervention that asks people to describe what they think are important vaccine uncertainties. Furthermore, by examining the relationship of attitudes to ‘anti-vaxxers’ with the cognitive-affective model of vaccine acceptability, the research indicates the potential significance of uncertainty and fear upon social attitudes.