Social media is an important tool to share credible messages to help address fears and misinformation. During the Ebola and Zika outbreaks, public health agencies use social media to communicate disease prevention messages to the public. Cate Shockey from CDC’s Office of Public Health Preparedness and Response will discuss the agency’s use of social media during the Ebola Emergency Response, and its subsequent influence on the Zika response. Isaac Chun-Hai Fung (Georgia Southern University) will present an analysis of retweeting and following networks of Ebola-related Twitter data, a study led by Hai Liang and King-Wa Fu (University of Hong Kong). They identified that the way Ebola-related information spread on Twitter was more like a broadcast spreading mechanism rather than viral spreading. Unlike social networks with viral spreading, the initial tweeters and their messages are much more important than common users if the broadcast spreading mechanism is dominant. Therefore, “influential” or “hidden influential” sources (e.g., social media accounts operated by traditional mass media) would be important partners to disseminate Ebola-related health information. Itai Himelbolm (University of Georgia) will present a network analysis of Zika-related Twitter data. Mapping patterns of social networks of the Zika Twitter discourse helped identify key communities discussing issues, their key information sources and the passages of information flow across communities. These networks and communities were not consistent across Zika-related topics. Himelbolm and colleagues also identified how information flowed via different social mediators and a range of communities, across a variety of Zika-related topics.