LAUSR

Significance During a pandemic, governments face incentives to not disclose negative information about vaccines to not jeopardize public vaccine acceptance. Against these incentives, the current study provides an experimental, cross-national demonstration of the importance of transparency in communication about a vaccine against COVID-19. While disclosing negative information may increase hesitancy, transparency sustains trust in health authorities and hinders the spread of conspiracy beliefs. Accordingly, the current results provide a clear warning against succumbing to the short-term incentive of withholding information. Sustaining trust during the pandemic is critical for health authorities, both if repeated vaccinations are necessary and in preparation for future health emergencies. Among those who have already lost trust, health communication has little persuasive effect. During the rapid development and rolling out of vaccines against COVID-19, researchers have called for an approach of “radical transparency,” in which vaccine information is transparently disclosed to the public, even if negative information can decrease vaccine uptake. Consistent with theories about the psychology of conspiracy beliefs, these calls predict that a lack of transparency may reduce trust in health authorities and may facilitate the spread of conspiracy theories, which may limit the long-term capabilities of health authorities during and after the pandemic. On the basis of preregistered experiments conducted on large, representative samples of Americans and Danes (N > 13,000), the current study contrasts the effects of vague vaccine communication with transparent communication, which discloses either positive or negative vaccine features. The evidence demonstrates that transparent negative communication may indeed harm vaccine acceptance here and now but that it increases trust in health authorities. Furthermore, the alternative of vague, reassuring communication does not increase vaccine acceptance either and leads to both lower trust and higher endorsement of conspiracy theories.