Mass media is recognized in health communication as a gatekeeper, alerting the public to what is important with a focus on accuracy and relevancy. This is done through media framing, by which mass media sets the tone through which the public will view the message. Social media has emerged as a force in health communication with the same potential for media framing as mass media; however, with social media there is no formal gatekeeper. Looking at two major disease outbreaks, Ebola and Zika, this chapter examines the influence and effect of social media on health communication. The Zika outbreak in Miami was examined with social listening methods to determine both the effect of mass media on social media and of social media on the effectiveness of traditional health communication outlets to spread their message. The authors conclude that social media is both an asset and a liability during disease outbreaks, and its effect depends on audiences' cultural attitudes and trust toward authorities and the media.