In December 2019, Wuhan, in Hubei province, China, became the center of an outbreak of pneumonia of unknown cause. In a short time, Chinese scientists had shared the genome information of a novel coronavirus (SARS-CoV-2) from these pneumonia patients and developed a real-time reverse transcription PCR (real time RT-PCR) diagnostic assay.

Whilst the outbreak is likely to have started from a zoonotic transmission event associated with a large seafood market that also traded in live wild animals, it soon became clear that person-to-person transmission was also occurring. The number of cases of COVID-19 identified in Wuhan increased markedly over the later part of January 2020, with cases identified in multiple other Provinces of China and internationally. Mathematical models of the expansion phase of the epidemic suggested that sustained person-to-person transmission is occurring, and the R-zero is substantially above 1, the level required for a self-sustaining epidemic in human populations.

The clinical spectrum of COVID-19 appears to be wide, encompassing asymptomatic infection, a mild upper respiratory tract illness, and severe viral pneumonia with respiratory failure and even death. Although the per infection risk of severe disease remains to be determined, and may differ from the initial reports of 10-15%, the large number of cases in Wuhan has resulted in a large number of patients hospitalised with pneumonia. Progression from prodromal symptoms (usually fever, fatigue, cough) to severe pneumonia requiring supplementary oxygen support, mechanical ventilation, or in some cases ECMO appears to occur most commonly during the second week of illness in association with persistent viral RNA detection. This provides a window of opportunity to test candidate antiviral therapeutics.

This new coronavirus, and previous experiences with SARS and MERS-CoV, highlight the need for therapeutics for human coronavirus infections that can improve clinical outcomes, reduce risk of disease progression, speed recovery, and reduce the requirements for intensive supportive care and prolonged hospitalisation. In addition, treatments for mild cases to reduce the duration of illness and infectivity may also be of value were COVID-19 to become pandemic and/or endemic in human populations.

Given no specific antiviral therapy for COVID-19 and the availability of remdesvir as a potential antiviral agent based on pre-clinical studies in SARS-CoV and MERS-CoV infections, this randomized, controlled, double blind trial will evaluate the efficacy and safety of remdesivir in patients hospitalized with mild or moderate COVID-19.