This research aims to identify communication strategies to improve the uptake of vaccines using an experimental design, focusing on the Human Papillomavirus (HPV) vaccine, which is highly effective in preventing HPV-related cancers. However, low HPV vaccination rates among adults remain a significant public health challenge. Although randomized controlled trials (RCTs) have demonstrated that interventions can increase vaccine uptake in children, few RCTs have been conducted on adults. To address this gap, a multidisciplinary investigative team with expertise in communication, medicine, nursing, and behavior-change intervention research, and a history of extensive collaboration, will conduct a survey experiment on a national sample of over 3,689 adults to identify the most promising theory-based messages to strengthen HPV vaccine intentions.