THE BEHAVIORAL IMMUNE SYSTEM AND VACCINATION INTENTIONS 1 Please note that this manuscript has not yet been published. Uploaded to PsyArXiv 4.3.2021. The Behavioral Immune System and Vaccination Intentions During the Coronavirus Pandemic Linda C. Karlsson1*, Anna Soveri2, Stephan Lewandowsky3, Linnea Karlsson4, Hasse Karlsson5, Saara Nolvi6, Max Karukivi7, Mikael Lindfelt8, and Jan Antfolk9 1Department of Psychology, Åbo Akademi University, Finland; [email protected] 2FinnBrain Birth Cohort Study, Department of Clinical Medicine, University of Turku, Finland; [email protected] 3School of Psychological Science, University of Bristol, United Kingdom; and School of Psychological Science, University of Western Australia, Australia; [email protected] 4FinnBrain Birth Cohort Study, Department of Clinical Medicine, University of Turku, Finland; the Centre for Population Health Research, University of Turku and Turku University Hospital, Finland; and Department of Pediatrics, Turku University Hospital and University of Turku, Finland; [email protected] 5FinnBrain Birth Cohort Study, Department of Clinical Medicine, University of Turku, Finland; Centre for Population Health Research, University of Turku and Turku University Hospital, Finland; and Department of Psychiatry, Turku University Hospital and University of Turku, Finland; [email protected] THE BEHAVIORAL IMMUNE SYSTEM AND VACCINATION INTENTIONS 2 6FinnBrain Birth Cohort Study, Department of Clinical Medicine, University of Turku, Finland; and Turku Institute for Advanced Studies, Department of Psychology and Speech- Language Pathology, University of Turku, Finland; [email protected] 7FinnBrain Birth Cohort Study, Department of Clinical Medicine, University of Turku, Finland; and Department of Psychiatry, Turku University Hospital and University of Turku, Finland; [email protected] 8Department of Theological Ethics, Åbo Akademi University, Finland; [email protected] 9Department of Psychology, Åbo Akademi Univerity, Finland; [email protected] Declarations of interest: none *Address correspondence to Linda C. Karlsson, Department of Psychology, Åbo Akademi University, Tehtaankatu 2, 20500, Turku, Finland, e-mail: [email protected], phone number: +358 40 8244119 Funding: This work was supported by the doctoral network of Minority Research at Åbo Akademi University; the Academy of Finland [grant numbers 316004, 316726]; and the Polin Institute. © 2021. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/ THE BEHAVIORAL IMMUNE SYSTEM AND VACCINATION INTENTIONS 3 Abstract The behavioral immune system is considered to be a psychological adaptation that decreases the risk of infection. Research suggests that, in the current environment, this system can produce attitudes with negative health consequences, such as increased vaccine hesitancy. In three studies, we investigated whether two facets of the behavioral immune system— contamination aversion (i.e., avoiding potential contamination) and perceived infectability (i.e., perceived susceptibility to disease)—predicted intentions to accept COVID-19, influenza, and measles or general childhood vaccinations. Both contamination aversion and perceived infectability were higher during than before the pandemic. In contrast to previous research, those with higher contamination aversion during the pandemic perceived vaccines to be safer and had higher intentions to accept vaccination. Contamination aversion before the pandemic was not associated with perceived vaccine safety or vaccination intentions during the pandemic. Individuals who perceived themselves as more susceptible to diseases were slightly more willing to accept vaccination. We conjecture that high disease threat reverses the relationship between the behavioral immune system response and vaccination. As the associations were weak, individual differences in contamination aversion and perceived infectability are of little practical relevance for vaccine uptake. Keywords: COVID-19; coronavirus; vaccination; vaccine hesitancy; behavioral immune system; perceived vulnerability to disease; disgust THE BEHAVIORAL IMMUNE SYSTEM AND VACCINATION INTENTIONS 4 1 INTRODUCTION Less than one year from the pandemic outbreak, researchers have developed safe and effective vaccines against the SARS-CoV-2 virus. Although some of these vaccines have efficacies in excess of 90% (Baden et al., 2021; Polack et al., 2020), successful suppression of the pandemic ultimately depends on the public’s acceptance of the vaccines. Research surveying acceptance rates before COVID-19 vaccinations begun indicated that 5–26% of individuals in European countries intended to refuse vaccination, and an additional 12–28% were unsure about their vaccination decision (Detoc et al., 2020; Freeman et al., 2020; Neumann-Böhme et al., 2020; The COCONEL Group, 2020; Ward et al., 2020). In the US and Canada, 14–25% indicated that they would refuse COVID-19 vaccination (Reiter et al., 2020; Taylor et al., 2020), whereas 7% of individuals in Australia reported that they would definitely or probably not accept a COVID-19 vaccine (Faasse & Newby, 2020). Deciding whether to take a vaccine is a complex psychological process affected by several factors. Research has demonstrated that attitudes towards the vaccine-preventable disease, as well as beliefs regarding the safety and effectiveness of the vaccines, play a key role in explaining vaccine hesitancy (Betsch et al., 2018; Brewer et al., 2017; Larson et al., 2014; Thomson et al., 2016). This means that understanding the psychology behind these driving attitudes is of considerable importance for ensuring sufficient uptake of COVID-19 vaccines. In the present study, we investigated to which degree dispositional differences related to psychological disease-avoidance mechanisms—the behavioral immune system—explain people’s intentions to accept a COVID-19 vaccine as well as their concerns regarding its safety. The behavioral immune system includes emotional, cognitive, and behavioral mechanisms that during our evolutionary history have decreased the risk of infection. 1.1 Mechanisms of the Behavioral Immune System THE BEHAVIORAL IMMUNE SYSTEM AND VACCINATION INTENTIONS 5 The detrimental effects of infectious diseases on survival are assumed to have resulted in the selection of psychological mechanisms, across evolutionary time scales, that decreased the risk of pathogenic contamination. These psychological adaptations have been labeled the behavioral immune system (Schaller, 2006; Schaller & Park, 2011). The behavioral immune system evolved to identify potential sources of pathogens in the environment and motivate avoidance of these sources by eliciting disgust (Curtis et al., 2011; Oaten et al., 2009; Schaller & Park, 2011; Tybur et al., 2013). As most pathogens cannot be directly observed, the behavioral immune system responds to environmental cues that in our past correlated with the presence of pathogens. Examples of such cues include spoiled food, the smell of biological decay, bodily secretions (e.g., saliva, nasal secretion, mucus), and wounds (Oaten et al., 2009). Because pathogen cues are not perfectly correlated with the actual presence of pathogens, the system might erroneously activate when pathogens are not present or fail to activate when pathogens are present. As failing to react to existing pathogens tend to have more detrimental consequences than reacting in their absence, the system evolved to be hypersensitive (Ackerman et al., 2018; Schaller & Park, 2011). The behavioral immune system therefore occasionally responds to cues that pose no actual infection threat. This hypersensitivity leads us to avoid healthy and nutritious food sources that smells like spoiled food (e.g., fermented fish, aged cheese) or avoid social contact with individuals who have deformities that are not contagious. Avoiding potential sources of pathogens comes with both benefits (e.g., successful avoidance of contaminated food) and costs (e.g., missed opportunity to get nutrition). The cost–benefit ratio is a trade-off that the individual must balance, and that depends on how vulnerable the individual is to infection. The behavioral immune system is, therefore, assumed to be flexible: when individuals perceive the situation to have high contamination risk, and perceive themselves to be more vulnerable, they are expected to be more attentive to THE BEHAVIORAL IMMUNE SYSTEM AND VACCINATION INTENTIONS 6 pathogen cues and react more strongly to them (Ackerman et al., 2018; Schaller & Park, 2011). 1.2 The Behavioral Immune System and Vaccination The behavioral immune system has been found to be related to a wide range of attitudes and behaviors humans display in the modern environment. Unsurprisingly, the behavioral immune system has been shown to be involved in attitudes and behaviors that promote health (Murray & Schaller, 2016; Schaller et al., 2015). However, the behavioral immune response may also have negative health consequences. For example, considering oneself vulnerable to infection is related to reduced sociability. At the same time, social isolation and loneliness is associated with long-term, negative health outcomes (Murray & Schaller, 2016; Schaller et al., 2015). Another area where the behavioral immune response might have negative health consequences is in making decisions about vaccination. Because the purpose of vaccination is to protect against infectious diseases,