**Principal investigator(s):** **Stephanie Demora** University of Pennsylvania Email: stephanie.demora@appc.upenn.edu Homepage: http://www.stephaniedemora.com/ **Jennifer Merolla** University of California Riverside Email: merolla@ucr.edu Homepage: https://www.jennifermerolla.com/ **Brian Newman** Pepperdine University Email: brian.newman@pepperdine.edu Homepage: https://seaver.pepperdine.edu/academics/faculty/brian-newman/ **Elizabeth Zechmeister** Vanderbilt University Email: liz.zechmeister@vanderbilt.edu Homepage: https://my.vanderbilt.edu/zechmeister/ **Sample size:** 3058 **Field period:** 10/28/2021-02/28/2022 **Abstract** Public resistance undermines health messaging campaigns. Theory suggests values-consistent rhetoric and source cues may soften resistance. We assess those expectations in opinion dynamics around U.S. Republicans’ views on the COVID-19 vaccine. We use original data from a pre-registered experiment embedded in national survey of Republicans (n = 3,058). Respondents were randomly assigned to one of three treatments or a control (no message) condition. Treated individuals received a message emphasizing core Republican values – liberty and patriotism in choosing to vaccinate, attributed to a public health official (treatment 1), a Republican voter (2), or a Democratic voter (3). The messages either had no effect or, more often, produced a backlash that led Republicans to express less favorable dispositions toward vaccination; that backlash was stronger for messages sourced to a Democratic or public health official. We conclude values-consistent messages may be of limited use, and in fact can backfire, in highly polarized contexts. **Hypotheses** H1: Republicans exposed to the patriotism message will be more inclined to get a vaccine, see benefits to vaccination, encourage others to get a vaccine, and support policies around vaccines. H1a: The hypothesized effects in H1 may be more pronounced among the most conservative since these values are particularly important to conservatives. H2a: The Republican source cue will increase the effect of the message. H2b: The Democrat source cue will decrease the effect of the message. As a baseline source, we use a non-partisan public health official, since messaging related to vaccination is most likely to come from such a source. **Experimental Manipulations** The experiment was embedded in a national online survey of 3,058 Republicans (including “leaners”). NORC conducted the survey using the AmeriSpeak Panel. Following blocking on vaccination status, the realized sample consists of 1,640 vaccinated Republicans and 1,418 unvaccinated Republicans. Data collection ran January 14-February 1, 2022. The experiment included four conditions. The control condition received no message. The experimental manipulation consisted of the following message: Suppose a public health official (treatment 1) / Republican voter (treatment 2) / Democratic voter (treatment 3) made the following argument to encourage people to get the vaccine: ‘I appreciate people's concern about making their own choice about vaccines. The way I see it, getting the vaccine is patriotic. It’s a way to love this great country. We can help the people that make the US great and our economy. We can beat the virus like we've beaten so many enemies before.’ **Outcomes** *Vaccine intention* Prior to the treatment, participants were asked about their current vaccination status. Based on their answer, they were asked about their vaccination intentions, as follows: Those who report in the pretest if they are unvaccinated (5 to the first question) get asked: How likely are you to choose to get the COVID-19 vaccine? 0% - Extremely unlikely to 100% - Extremely Likely [slider] Those who report having one dose of Moderna or Pfizer in the pre-test (2 to the first question) get asked: How likely are you to choose to get the second dose of the COVID-19 vaccine? 0% - Extremely unlikely to 100% - Extremely Likely [slider] Those who report being fully vaccinated (1 or 2 to the first question above) but have not received a booster get asked: A “booster” is a vaccine dose that helps improve your body’s ability to fight an infection. How likely are you to choose to get the COVID-19 booster? 0% - Extremely unlikely to 100% - Extremely Likely [slider] Those who report being fully vaccinated (1 or 2 to the first question above) and have received a booster get asked: If an additional booster vaccine for COVID-19 were recommended by health officials and offered to you in the next year, how likely would you be to get an additional booster? 0% - Extremely unlikely to 100% - Extremely Likely [slider] *Vaccine Benefits* The next set of questions ask about perceptions of the benefits of vaccines: How much do you agree with the following statements? A. The benefits of COVID-19 vaccines are much greater than the risks. B. Americans have a responsibility to get a COVID-19 vaccine. C. If a large majority of Americans get a COVID-19 vaccine, it would help the economy a lot. 0 - Strongly Disagree to 100 - Strongly Agree [slider] *Vaccine Encouragement* The next set of question assesses if respondents will encourage others to get vaccinated. Consider a case in which you have a friend or family member who is unsure whether to get the COVID-19 vaccine. On the below scale, what best captures how you would respond to this person? You can pick any number from 0 to 100. 0 - Strongly discourage them from getting the vaccine / 50 - Neither encourage nor discourage them from getting the vaccine / 100% - Strongly encourage them to get the vaccine [slider] *Views toward vaccine mandates* The final two questions ask about support for vaccine mandates: Some people, such as the elderly, people with cancer, lung disease, or other medical conditions, are at greater risk for getting severely ill from COVID-19. Allowing for religious and other exemptions, to what extent do you oppose or support employers deciding to mandate the vaccine for their employees who act as caretakers for such populations? 0 - Strongly Oppose to 100 - Strongly Support [slider] Some colleges and universities in the U.S. have mandated that students and staff be vaccinated against COVID-19 to participate in on-campus in-person activities, often allowing religious and other exemptions. To what extent do you oppose or support these policies? 0 - Strongly Oppose to 100 - Strongly Support [slider] **Summary of Results** We find mixed support for H1. Across the different forms of vaccination intentions, the most common outcome is that the message reduced intentions. For unvaccinated Republicans, there was no discernable treatment effect for the message with the Republican or public health source cue and Republicans receiving the message with a Democrat source cue were 3 percentage points less likely to anticipate vaccinating (all results reported here significant at p < .05). Among Republicans who have had only one of a two shot vaccine sequence, exposure to the message reduces reported likelihood of getting a second dose by 16.3 percentage points (Democrat source), 21.5 pp (public health official), and 39.3 pp (Republican source). Among Republicans who received a full initial vaccination sequence but no booster, exposure to the public health cued message reduces reported likelihood of getting a booster by 7.2 percentage points, while intentions were unmoved in other conditions. Only one result was consistent with expectations: for Republicans who are vaccinated and boosted, the message increases reported likelihood of another booster if recommended by health officials by 5.1 and 7.4 percentage points in the Democrat and Republican source conditions, respectively. We find no support for H1a. For those in the public health condition, backlash is concentrated among the most conservative for intention to get a booster shot, intent to encourage others to vaccinate, and support for vaccine mandates for students and caretakers. Counter to H2a, the message with a Republican source cue either has no impact on vaccination attitudes or makes attitudes more negative. Republicans in this condition scored 4.5 points lower on believing Americans have a responsibility to get the vaccine, 3.6 points lower on believing that it would help the economy, and 5.8 lower on believing there should be vaccine mandates at colleges and universities. Consistent with H2b, compared to those in the control condition, exposure to the message attributed to a Democrat decreases favorable attitudes toward the vaccine on all measures. Belief that the benefits of vaccination outweigh the costs decreases by 4.8 points; that Americans have a responsibility to get the vaccine decreases by 7.3 points; that if a large majority of Americans got the vaccine it would help the economy decreases by 7.4 points; willingness to encourage a friend or family member to get a vaccine by 4.4 points; support for a vaccinate mandate for healthcare workers who treat vulnerable populations by 9.4 points; and support for mandates at colleges and universities by 9.1 points. The same pattern of results appears when individuals are exposed to a values-consistent message attributed to a public health official.