Purpose: Although Human Papilloma Virus (HPV) is the most commonly diagnosed sexually transmitted infection in the USA, much controversy exists with respect to HPV vaccination, especially among parents of adolescents. Previous research has shown that exemplars in the media influence public opinion estimates about controversial social issues. However, little is known about the underlying psychological processes of how exemplars influence public opinion formation. The purpose of this paper is to systematically explore such psychological processes based on the projection theory. To this end, the important yet controversial public health issue, the mandatory HPV vaccination, was chosen. Design/methodology/approach: A two-factor (exemplar vs proportion), between-subject experiment was conducted using online newspaper articles as main stimuli. A total of 138 participants completed the study. The analytical framework comprised the Sobel test with the Bootstrap method and a series of Ordinary Least Square hierarchical regression analyses. Findings: The higher the proportion of exemplars against the HPV vaccination in a news article was, the greater the number of individuals who became opposed to it was. And the high personal opposition translated into negative public opinion change estimation. Originality/value: The findings indicate that news exemplars may influence individuals' personal opinion formation, and, in turn, contribute to their estimations of future public opinion climate, as suggested by the projection theory. Theoretical, methodological and practical implications for journalists, health educators and policy makers are discussed.