Background: In a pandemic, when timely and clear communication is important, visuals on social media can help citizens quickly find and understand health risk information. In recognition of visuality and social media’s value during a crisis, we investigated popular Covid-19 risk communication with visuals posted on the platform Twitter. Looking at tweet authors, their use of graphics, the preventative messages, and risk framing, our objective was to determine how visual communication on Twitter promoted WHO Covid-19 health recommendations.Methods: We sourced Twitter’s 500 most retweeted Covid-19 messages for each month from January - October 2020 using Crowdbreaks. Included tweets had to have visuals, be in English, come from verified accounts, and contain at least one of the keywords ‘covid19', 'coronavirus', 'corona', or 'covid’. Following a retrospective approach, we then performed a qualitative content analysis of the tweets’ text and visuals. Results: Most of the tweets analysed came from influencers - individuals with many followers (51%), followed by media companies (30%), and health and government institutions (15%). At the start of the pandemic, the latter two were most prevalent. Analysis of visual formats showed that photographs were most common, and the majority of tweets combined them with other graphic types (55%). 68% of tweets had text in their visual, 42% of all visuals were animated, and 26% included a URL. ‘Stay home’ and ‘wear a mask’ were the most frequently communicated Covid-19 preventative measures. 70% of tweets used risk framing (emphasising health gains or loss), and 32% had tones of critique.Conclusion: This study found that the most retweeted Covid-19 preventative measures with visuals mostly came from individuals, showing that health and government organisations were not alone in promoting preventative measures on Twitter. This stresses the important role individuals play in the dissemination of information using social media during a health crisis. The finding that more tweets used health loss framing, often combined with the emotive medium of photographs, raises concerns about persuasive tactics feeding on fear. Future research is needed to better understand this approach's consequences and its impact on public perceptions and behaviours.