Nonscientific mindsets and the gap between past vaccine behaviors and future intentions.

Use of complementary and alternative medicines (CAM) is often associated with vaccine hesitancy. However, the nature of-and reasons for-this association are obscure as CAM and vaccine hesitancy are both complex, heterogeneous phenomena. This study aims to identify which aspects of CAM are associated with vaccine hesitancy and to probe the psychological roots of that association. Over two recruitment stages (N₁ = 1,905, N₂ = 1,443), participants from Argentina, Germany, and the United States reported vaccine/CAM behaviors, intentions, and beliefs. They also responded to scales probing nonscientific mindsets, including negative attitudes to expertise and anomalous belief formation. An item response theory model of vaccine responses revealed that, outside of total acceptance or outright refusal, vaccine hesitancy reflected a gap between past vaccination behaviors and future behavioral intentions. Vaccine hesitancy was weakly predicted by CAM use but was better predicted by certain CAM beliefs, particularly an oppositional view of natural versus biomedical care. Nonscientific mindsets showed similar patterns of association with vaccine hesitancy and with aspects of CAM beliefs. Observed associations between CAM and vaccine hesitancy are primarily a matter of health-relevant beliefs centered on natural versus scientific medicine. This relationship-and in particular, the gap between past vaccine behaviors and future behavioral intentions-reflects nonscientific mindsets. Thus, a key challenge in addressing this form of vaccine hesitancy is one of perspective taking: Scientists must find persuasive reasons to vaccinate which still appeal to some who do not see science as the main route to medical knowledge. (PsycInfo Database Record (c) 2025 APA, all rights reserved).