Sharing of preprints-scientific manuscripts that are posted in a publicly accessible, online repository before peer review for journal publication-can accelerate access to information in infectious disease outbreaks, according to an article published earlier this month by Michael Johansson and colleagues in PLOS Medicine. In an analysis of published articles and those posted on preprint servers, the authors found that preprint posting increased during the 2015-17 outbreak of Zika in the Americas relative to the 2014-15 Ebola outbreak in West Africa, and that preprints, while still used for only a small proportion of papers, provided much earlier access to scientific findings [1] . For medical journal editors who agreed in late 2015 and early 2016 that authors should not be penalized for sharing results in public health emergencies [2-4], these results signal gratifying progress over practices in 2003, when the severe acute respiratory syndrome (SARS) epidemic was shown to have ended before 93% of journal articles on the epidemiology of SARS were published [5] . PLOS Medicine has long permitted the posting of preprints for research articles submitted to the journal, and this remains our policy. For the most part, posting of preprints has been occasional, undertaken on the initiative of authors without the journal's involvement. In the coming months, PLOS journals that handle research in more basic biological fields will begin facilitating preprint posts of journal submissions, with author approval, on the bioRxiv preprint server operated by Cold Spring Harbor Laboratory [6] . PLOS Medicine will not initially be offering transfer of submitted manuscripts to bioRxiv as preprints. Because the journal's scope encompasses clinical and policy-related research, we believe it is important now to establish appropriate standards for the early sharing of research that has potential implications for human health but has not been peer reviewed. As preprint servers for clinically focused research become more widely available and preprint posting becomes more routine and more closely integrated with journal publishing, editors of medical journals should join the conversation about best practices for preprint sharing in medical research. In calling for wider use of preprints, Johansson and colleagues note the importance of protecting participant confidentiality, ensuring that posted research was ethically conducted, and guarding against misinterpretation of results that have yet to undergo peer review, either by traditional journal routes or through newer, more public venues [1] . In medical research, competing interests have been shown to be associated with reported outcomes [7] , and editors and peer reviewers persuade authors to tone down overstated conclusions prior to publication as a matter of course. At the same time, the press and other media networks are expected to disseminate the latest available information, and even readers with an urgent interest in a given health-related topic may be hard pressed to assess the validity of research methodology. As publication practices evolve, what is the best way for the medical research community to fulfill PLOS Medicine | https://doi.org/10.1371/journal.pmed.
Output: Preprints in medical research: Progress and principles