Availability of COVID-19 preprints has also accumulated at higher rates than preprints addressing both cholera, of which there has been an epidemic in Yemen since late 2016 \citep{camacho_cholera_2018}, and influenza virus, considering the onset the seasonal influenza epidemic in 2019 for comparability (Table 1). However, research addressing cholera and influenza initiated sooner after the first reported cluster (Figure 2), likely reflecting a level of constant research attention given the endemicity of these diseases.
Whilst an increase in preprint accumulation beyond prior outbreaks is to be expected due to growth in preprint recognition in recent years \cite{asapbio_biology_2019}, the magnitude of acceleration for COVID-19 preprints is remarkable when considering the modest rates of preprint development over multiple seasonal influenza periods as a benchmark (Supplementary Figure).

Preprints in the context of the wider epidemic response

This exceptional speed of preprint development has been just one component of a paradigm shift towards rapidly mobilised, open-platform research in outbreak responsiveness. This new scientific territory investigating COVID-19 has also involved rapid development and sharing of SARS-CoV-2 genome sequences through dedicated repositories, e.g. GISAID’s surveillance network \citep*{shu_gisaid_2017} and digital workspaces for rapid international communication \cite{kupferschmidt_preprints_2020}.
While preprint infrastructure has shown clear effectiveness and value in making novel COVID-19 findings swiftly available, evaluating its influence in active outbreak control is difficult. Preprints regarding estimates of R0 have been linked to influence upon policy and media interest based on news reporting and search trends \citep*{majumder_early_2020}, though more specific impacts of preprints will require citation tracing and meta-research over the full course of the epidemic.
Although effective at distributing knowledge, preprint servers have been critiqued as not fulfilling an intended function of developing peer discussion \cite{anderson_biorxiv_2019}. Several external platforms aim to facilitate this pre-review commentary, including the Outbreak Science Rapid PREreview platform for active epidemics (https://outbreaksci.prereview.org/). However, community uptake has been slow. Pre-review feedback has been requested for 50 COVID-19-related preprints to date, of which only 9 have received any. Peer discussion around COVID-19 research appears more likely to take place on platforms featuring novel results not yet in article format, such as Virological (https://virological.org). Better integration of peer discussion into existing preprint platforms may improve the efficiency and transparency of research responses to future epidemics.