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The Covid-19 pandemic led to unprecedented exposure of scientific activity in the public sphere, in which social media played a key role, eliciting both enthusiasm and concern about the changing relationship between science and society. This article focuses on the exceptional retraction of an article from the journal The Lancet – widely commented on as Lancet Gate – under fire from critics on Twitter. The article in question, published on 22 May 2020, reopened the debate on the efficacy of hydroxychloroquine and sparked a massive controversy on Twitter, leading to its retraction on 6 June. Some commentators saw this sequence as a victory for the collective vigilance enabled by Twitter, acting as a platform for ‘post-publication peer review’ (PPPR). Drawing on a survey combining analysis of online interactions and interviews, we describe in detail the conditions of attention and mobilization on the platform. Although many researchers were present and expressed themselves, their criticism remained largely individual, diluted in largely politicized and polarized commentaries, leading above all to a ‘disorganized scepticism’ made up of a juxtaposition of positions.