Background: One of the most effective tools to reduce cancers linked to sexually transmitted viruses is the HPV vaccine. In social media, portrayals of the vaccine tend to present its risks at a higher level than current scientific data suggests. In this online experiment, we investigate how a Facebook post affects users’ perceived likelihood and severity of adverse reactions to the vaccine (VAEs), and how these and users’ relationship to health literacy affect the likelihood of interacting with the message (i.e., likes). Method: An online survey was distributed to students at two US universities, and residents in Illinois and Texas (n=721). We used path analysis to empirically examine the relationship between several predictors (e.g., likelihood and severity of VAEs, HPV vaccination experience, health literacy) on willingness to interact with an HPV vaccine-related post. Results: The hypothesized model reflects a relationship between the predictors and outcome behavior (χ2 (13)=133.03, p<.001; RMSEA=0.04). Subjects’ health literacy had a direct and positive impact on the likelihood of VAEs (beta=0.186, p<.01) and indirectly, through the perceived number of VAEs with perceived severity of VAEs. Perceived severity of VAEs had a negative and indirect relationship with readiness for liking the Facebook post (beta=0.219, p<.01). Conclusions: The results of this study suggest a mechanism for how a post found in social media is more likely to be shared and information on VAEs be communicated. Understanding these mechanisms can lead to new communication strategies in social media.