The current outbreak of COVID-19 has escalated into a global health crisis. Investigations into the epidemic have taken place upon an unprecedented stage of rapid, open-platform science, including vastly improved access to unreviewed preprint research.I quantified preprint responses to COVID-19 by examining 785 preprints posted to English-language preprint servers (bioRxiv, n = 140; medRxiv, n = 561; arXiv, n = 84). Preprint research during the current outbreak has been enormously accelerated, with an average of 11.9 preprints posted per day – over a hundred-fold higher than that during 2014’s West African ebolavirus outbreak.While this boom in preprints has enabled valuable knowledge sharing of scientific developments, novel challenges have become apparent. Unfounded conclusions from unreviewed research have played a clear role in public misinformation about the epidemic. I provide recommendations to improve accountability and transparency surrounding preprints, a vital step for future outbreaks as open-platform epidemiology continues to advance.