This study examines whether social media exposure is associated with the public's beliefs and misbeliefs about human papillomavirus (HPV) vaccination and how those (mis)beliefs are associated with the public's support for HPV vaccination-related policies. This study also explores whether trust in HPV vaccination-related regulatory organizations moderates the associations between social media exposure and public policy support through (mis)beliefs. We found that social media exposure was positively associated with misbeliefs about HPV vaccination. The findings also indicated that while beliefs about benefits were positively associated with policy support for HPV vaccination, misbeliefs were negatively associated with this support. More interestingly, our analysis revealed that the negative association of HPV-related misbeliefs with vaccination policy support was larger for those who had low levels of trust, compared to their high-trust counterparts.