Project Summary Background: Misinformation on social media, or the sharing of false or incomplete information without intent to cause harm, is contributing to vaccine hesitancy among parents and impeding uptake of the HPV vaccine among adolescents in the United States. Innovative communication strategies that can be rapidly developed and deployed to correct evolving misinformation about HPV vaccine on social media and increase uptake of HPV vaccine are needed. Hypothesis: We hypothesize that theory-based corrective messages directly addressing the content of misinformation will improve HPV vaccine series initiation and completion as compared to general corrective messages and a non-message control group. Proposal: We will efficiently identify recently circulating misinformation on social media using natural language processing (NLP) methods, develop and test a theory-based corrective messaging tool using a validated message testing protocol, and assess the efficacy of the tool on increasing HPV vaccine series initiation and completion among adolescents in an online, block-randomized controlled trial with three arms and longitudinal follow-up. Participants (n=2500) will be parents of adolescents ages 8-11 recruited from social media and followed up over a 12-month period. Importance and Innovation: If successful, in addition to improving HPV vaccination uptake, the methods from this study have the potential to be adapted to address other forms of misinformation swiftly and efficiently in public health such as that surrounding COVID19, childhood vaccinations, or cancer prevention and treatment strategies.