The politics of visibility: who gets seen in digital health communication on Douyin

China has increasingly positioned digital health communication as part of its national public health strategy, with short video platforms promoted as accessible and engaging channels for reaching diverse publics. As the Chinese precursor of TikTok, Douyin has developed distinctive governance mechanisms that shape the visibility and legitimacy of health content. This study examines how health-related information was framed, presented, and circulated on Douyin, and whose voices became visible under conditions of heightened urgency and public attention. Based on a quantitative content analysis of 1,074 most-liked COVID-19-related videos, the study analyses video sources, themes, presentation styles, emotional tones, featured characters, and engagement metrics. The findings show that news media, health professionals, and official actors were the most visible contributors, producing cohesive narratives aligned with state priorities. Ordinary users participated mainly through personalised and affective expressions, but largely reinforced rather than disrupted institutional framings. By using COVID-19 as a strategic case of a public health emergency, this study captures a moment when platform dynamics, state policy, professional authority, and public participation became especially visible. It foregrounds how health information visibility is produced, structured, and constrained under conditions of heightened urgency and public attention.