The COVID-19 pandemic, declared in March 2020, presented an unprecedented global health crisis. With millions infected and hundreds of thousands dead, the economic repercussions were also catastrophic. In the absence of effective treatments, physical distancing and quarantine measures were implemented globally. The urgent need for a vaccine to protect populations and economies became paramount. Early clinical trials commenced in March 2020, and by September 2020, some vaccines had progressed to Phase 3 trials, indicating promising progress toward vaccine availability. However, studies revealed significant vaccine hesitancy and resistance within European populations, creating a critical challenge for effective vaccine deployment. Understanding the reasons behind this hesitancy became crucial. Previous research on vaccine hesitancy often focused on explicit reasons for opposition, lacking in depth explanations for underlying beliefs. A more effective strategy would be identifying the psychological processes driving vaccine hesitancy and resistance and comparing those attitudes against those receptive to vaccines—an approach drawing inspiration from the “attitude roots” model of science rejection. This approach might uncover the psychological drivers of vaccine hesitancy and would help tailor public health messages to resonate more effectively with hesitant or resistant individuals. Past research has explored psychological constructs like altruistic beliefs, personality traits (neuroticism, conscientiousness), locus of control, and cognitive reflection in relation to vaccine acceptance. Conspiracy theories, religious beliefs, and mistrust of authorities have also been linked to vaccine hesitancy. The goal of this study was to better understand the interplay of these factors in determining COVID-19 vaccine acceptance, hesitancy, and resistance.

Existing literature on vaccine hesitancy and resistance primarily focused on the explicit reasons given by individuals for their opposition. While providing valuable insights, these studies often lacked the depth to explain the deeper epistemological positions driving vaccine rejection. Researchers argued for a focus on the psychological processes underlying these attitudes, drawing on the "attitude roots" model of science rejection. This model highlights the importance of identifying psychological mechanisms that shape individuals' beliefs and attitudes, rather than solely examining stated reasons. This approach offers a more complete explanation of why individuals hold their respective views and enables more effective targeting of tailored public health messages that are consistent with those individuals' psychological dispositions. Public health campaigns aimed at influencing health behaviors have demonstrated the benefits of psychologically-informed approaches. Studies have considered various psychological factors influencing vaccine acceptance, including altruistic beliefs, personality traits (neuroticism and conscientiousness), locus of control, cognitive reflection, and beliefs about conspiracies, religion, and authority figures. Mistrust of authority figures and negative attitudes towards migrants have also been linked to vaccine hesitancy.

This study utilized data from nationally representative samples of the general adult populations of Ireland (N=1041) and the UK (N=2025). The data was collected by Qualtrics, a survey company, as part of the COVID-19 Psychological Research Consortium (C19PRC) Study. Quota sampling ensured that sample characteristics matched known population parameters for age, sex, and geographic distribution in both countries. Data collection in the UK occurred between March 23rd and 28th, 2020, and in Ireland between March 31st and April 5th, 2020—both times during strict lockdown measures. The study included individuals aged 18 or older, residing in Ireland or the UK, and able to complete the survey in English. Participants completed online surveys and were compensated for their time. Ethical approval was obtained from the University of Sheffield and Ulster University. The study employed various measures to assess the following: COVID-19 vaccination status, sociodemographic, political, and religious indicators, health-related indicators, personality traits (using the BFI-10), locus of control (using the LoC Scale), analytical/reflective reasoning (using the CRT), altruism (using the IWAH), conspiracy beliefs (using the CMS), paranoia (using the PaDS), religious and atheist beliefs (using the Monotheist and Atheist Beliefs Scale), trust in institutions, authoritarianism (using the VSA), social dominance (using the SDO), attitudes toward migrants, and COVID-19 information consumption and trust. Data analysis included calculating proportions of vaccine acceptance, hesitancy, and resistance; multinomial logistic regression analyses to identify sociodemographic, political, and health-related indicators associated with hesitancy and resistance; ANOVAs with Bonferroni post-hoc tests to compare psychological characteristics across vaccine response groups; and ANOVAs to compare information sources and trust levels.

In Ireland, 65% of respondents were accepting of a COVID-19 vaccine, 26% were hesitant, and 9% were resistant. In the UK, 69% were accepting, 25% hesitant, and 6% resistant. Northern Ireland showed the lowest vaccine acceptance rate (51%). Sociodemographically, women were more likely to be hesitant in both countries, and younger individuals were more likely to be hesitant or resistant. Lower income was associated with vaccine resistance in both countries. In Ireland, vaccine resistance was also linked to non-Irish birth status, city dwelling, voting for anti-establishment parties, and having underlying health conditions. In the UK, suburban dwelling and pregnancy were additional factors. Psychologically, those hesitant or resistant in both countries displayed lower trust in scientists, healthcare professionals, and the state; held stronger religious beliefs, conspiracy beliefs and paranoid beliefs; showed lower altruism; scored higher on social dominance and authoritarianism; demonstrated less agreeableness and conscientiousness, higher neuroticism; scored higher on internal locus of control; and showed lower levels of cognitive reflection. In terms of information sources, vaccine-resistant individuals consumed less information from traditional sources (newspapers, television, radio, government agencies) and more from social media, showing significantly lower trust in traditional sources.

The study's findings highlight substantial vaccine hesitancy and resistance in both Ireland and the UK, consistent with other European and US studies. While sociodemographic factors showed some country-specific variations, the psychological profiles of hesitant/resistant individuals were remarkably similar across both nations. These similarities suggest common underlying psychological mechanisms driving vaccine hesitancy regardless of specific contextual factors. The observed mistrust in traditional information sources and the preference for social media as an information source pose significant challenges for public health messaging. The findings suggest that public health campaigns should target specific groups (women, younger adults, lower socioeconomic groups), considering the unique risk factors in each country while adapting the messaging to resonate with the identified psychological characteristics (emphasizing self-interest, appealing to non-traditional authorities, and using clear, direct, repeated, and positive messaging).

This study reveals substantial COVID-19 vaccine hesitancy and resistance in Ireland and the UK, characterized by consistent psychological profiles across both populations. The findings highlight the importance of understanding these psychological factors for developing effective public health strategies that utilize multiple channels and tailored messaging to address concerns of specific demographic and psychological groups. Future research should explore the dynamic nature of vaccine hesitancy over time and across diverse populations.

The study used quota sampling via internet surveys, which might not fully represent the entire population, especially those who are not online or institutionalised. Data collection occurred during strict lockdowns, potentially influencing the results. The study also involved a hypothetical vaccine, limiting the generalizability to actual vaccine uptake. The study's focus on two western European countries limits the generalizability to other cultural contexts.