Abstract: 【Purpose/significance】It's hard for a crisis governor to voice properly and lead public opinion when facing tense and di?
verse environment in an international social platform.【Methods/process】World Health Organization (WHO) vaccine-related tweets
have been taken as a sample of emergent discursive practices. Under the guidance of communication theories, the paper systematically analyzes its agenda setting, frame setting, emotional polarity, release form, and social network, with the help of semantic network, LDA topic model, and aspect-based sentiment model to answer the question of When, What, How and Who.【Results/conclusion】The re? sults show that WHO achieved a positive effect via timely voicing, audience-oriented communication, emotional persuasion, multiple forms and other guidance and control strategies. But WHO fails to build a multi-agent alliance in cyberspace, and needs to adopt more multimodal forms in tweets.【Innovation/limitation】Discourse analysis can provide more detailed interpretation of statistical data and reveal the depth and sociality of public opinion, which is a useful interdisciplinary attempt. However, the study only focuses on the pro? cess itself, which is not comprehensive enough, so the evaluation results could be biased