The spread of COVID-19 misinformation on social media has elicited concern amongst scholars, health agencies and governments owing to its potential harms to public health. This article addresses the question of how networks of Australian health professionals engaged with COVID-19 facts and myths on Twitter between August and October 2020. After reviewing selected literature on COVID-19 misinformation, we present our analytical choices and the methodology we used to constitute datasets of COVID-19 factual and mythical hashtags and of verified Australian health professional accounts (N:377). The article distinguishes between the capacities of ‘actor-actants’ and ‘issue-actants’, and between the adoption of ‘field’ and ‘contested’ hashtags during a controversy. We identify categories of Australian health professional Twitter accounts such as GPs, nurses, specialists, public health professionals and researchers, and analyse the patterns of connections between these actor-actants and COVID-19 facts and myths. We find that these categories exhibit clearly distinct behaviour when tweeting or retweeting factual and mythical hashtags. Even though the rate of Australian health professionals’ connection with myths in comparison to facts on Twitter is low, hashtags such as #hydroxychloroquine attracted significant engagement. We examine these hashtags’ context and find that they were mainly being debunked, though a minority of accounts endorsed them. We analyse these adoption patterns, and critically assess the ‘echo chamber effect.’ We also consider public health and privacy implications for the dissemination of accurate information, for trust in health professionals during a pandemic, and for combatting misinformation.