Vaccination yields the direct individual benefit of protecting recipients from infectious diseases and also the indirect social benefit of reducing the transmission of infections to others, often referred to asherd immunity. This research examines how prosocial concern for vaccination, defined as people’s preoccupation with infecting others if they do not vaccinate themselves, motivates vaccination in more and less populated regions of the United States. A nationally representative, longitudinal survey of 2,490 Americans showed that prosocial concern had a larger positive influence on vaccination against influenza in sparser regions, as judged by a region’s nonmetropolitan status, lesser population density, and lower proportion of urban land area. Two experiments (totaln= 800), one preregistered, provide causal evidence that drawing attention to prosocial (vs. individual) concerns interacted with social density to affect vaccination intentions. Specifically, prosocial concern led to stronger intentions to vaccinate against influenza and COVID-19 but only when social density was low (vs. high). Moderated mediation analyses show that, in low-density conditions, the benefits of inducing prosocial concern were due to greater perceived impact of one’s vaccination on others. In this light, public health communications may reap more benefits from emphasizing the prosocial aspects of vaccination in sparser environments.

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In a survey and three experiments (one preregistered with a nationally representative sample), we examined if vaccination requirements are likely to backfire, as commonly feared. We investigated if relative to encouraging free choice in vaccination, requiring a vaccine weakens or strengthens vaccination intentions, both in general and among individuals with a predisposition to experience psychological reactance. In the four studies, compared to free choice, requirements strengthened vaccination intentions across racial and ethnic groups, across studies, and across levels of trait psychological reactance. The results consistently suggest that fears of a backlash against vaccine mandates may be unfounded and that requirements will promote COVID-19 vaccine uptake in the United States.

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Does the way individuals think about the burdens and benefits of giving time to charity depend on how that time is distributed? Prior work shows that the assessment of a whole is different than the assessment of the sum of its parts. Drawing on this work, we demonstrate that when a volunteer experience is segregated into multiple parts (vs. aggregated into a whole)-for example, volunteering 4 h a day for 2 days versus 8 h in a single day-individuals expect the process to feel less effortful but also the outcome to feel less morally right. In addition, we find that contribution size has a moderating effect on anticipated effort (but not on anticipated morality).Lastly, we find that individuals who focus on minimizing the effort involved in volunteering (vs. maximizing the impact of volunteering) show a greater likelihood of volunteering in a segregated (vs. aggregated) manner. We discuss theoretical and practical implications of these findings.

Objective: To determine the influence of two representative metrics of epidemiological risk, changes in new infections, and disease prevalence, on people's risk judgments and disease-prevention behaviors. Method: Four experiments were conducted from August 2020 to May 2021. In Experiments 1 and 2, participants were exposed to information about different directions of change (upward and downward) and varying levels of prevalence of an infectious disease. In Experiments 3 and 4, participants were exposed to information about only one direction of change (upward or downward) and varying levels of prevalence. Participants reported risk judgments and intentions to engage in disease-prevention behaviors for each disease situation presented to them. Results: When both the direction of change and levels of prevalence varied, risk judgments and intentions were more influenced by change (vs. prevalence) information. Participants’ reliance on prevalence information to guide risk judgments increased when they were presented with only an upward or downward change, particularly for situations with worsening infections. In all cases, the effects of epidemiological information on behavioral intentions were mediated by its effects on risk judgments. Conclusions: Information about changes in infections consistently influences people's risk judgments and drive subsequent behavioral response. The impact of prevalence information, however, is limited to situations in which changes in infections are stable, such that it affects risk judgments and behavior decisions only when changes in infections demonstrate a constant upward or downward direction. The results point to the need for public health interventions to increase the impact of prevalence information.

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To mitigate the opioid epidemic, a concerted effort to educate, prevent, diagnose, treat, and engage residents is required. In this study, a digitally distributed method to form a large network of organizations was tested with 99 counties in regions with high vulnerability to hepatitis C virus (HCV). The method involved a cascade of contacts going from email to phone calls, to videoconferencing and measuring the number of contacts required, amount of time taken, and the proportion of success at recruiting at least one community organization per county. A recruitment period of 5 months and 2118 contact attempts led to the recruitment of organizations from 73 out of our 99 target counties. Organizations belonging to health departments required more attempts and time to recruit but ultimately enrolled at higher rates than did other organizations such as coalitions and agencies. Organizations from counties more (vs. less) vulnerable to HCV outbreaks required more attempts to recruit and, using multiple recruitment methods (e.g., emails, phone calls, and Zoom meetings), improved enrollment success. Overall, this method proved to be successful at remotely engaging a large‐scale network of communities with different levels of risk within a large geographic region.