Of the antiviral, antibiotic, antiretroviral and anti-malarial medicines being studied in trials to treat and prevent Covid-19, a drug called remdesivir is among a handful which scientists and the World Health Organization consider most promising. Hope in the drug was revived on Wednesday when the US government’s top infectious disease expert, Dr Anthony Fauci, said data from one clinical trial “shows that remdesivir has a clear-cut, significant, positive effect in diminishing the time to recovery”. But within hours of Fauci’s announcement, the prestigious medical journal The Lancet published results from a study in China which found remdesivir did not speed recovery or reduce deaths from Covid-19 compared with a placebo in hospital patients. So what should the public make of the seemingly conflicting remdisivir results? What is remdesivir? Remdesivir is an experimental antiviral produced by the US pharmaceutical company Gilead, initially as a potential treatment for the Ebola virus. It was rapidly pushed through clinical trials after showing promising results in the lab, and was then rolled out more widely in affected areas of Africa. However, in 2019 Congolese health officials said the drug was less effective than monoclonal antibody drugs, which are often used for cancer treatment and had a much more significant impact on lowering death rates than remdesivir. Remdesivir has been revived with the outbreak of Covid-19. This is because it showed promising results in preventing Middle East Respiratory Syndrome (Mers-CoV) and severe acute respiratory syndrome (Sars), which are also caused by coronaviruses. But those studies have only been done in animals. What do we know about how it works? The drug is administered via daily infusion for about 10 days. Currently remdesivir has not been approved by health authorities around the world, and given it was mainly being used for Ebola, supply is low. But it is being used in clinical trials, and many countries are attempting to get access to the drug for use in their own Covid-19 studies. There has been spike in applications to Gilead for the drug from countries where Covid-19 has been particularly devastating. In previous animal studies of Mers-CoV, US researchers found remdesivir blocks a particular enzyme that is required for viral replication. Scientists hope it will have a similar effect on Covid-19. What did the US study show? The study praised by Fauci relates to a clinical trial by Gilead, sponsored by the National Institute of Allergy and Infectious Diseases in the US. The trial of more than 1,000 patients showed those given remdesivir improved after an average of 11 days, compared with an average of 15 days for those not given the treatment. There was no statistically significant improvement in survival rate between the two groups. Dr Elena K Schneider-Futschik, from the University of Melbourne’s department of pharmacology and therapeutics, said given the absence of other treatments for Covid-19 and the promising data from the study, “we can assume that the drug may be fast-tracked”. Gideon Meyerowitz-Katz, an epidemiologist with the University of Wollongong, said it was important to note the full study had not yet been published, and that although it found patients given the drug recovered faster, researchers had broadened their definition of “recovery” throughout the trial. “This isn’t necessarily bad in and of itself, but without further explanation it’s hard to understand why the study made the choices that it did,” he said. “For example, they included people who were still in hospital in their “recovered” figure, according to the study registration – until we see the full published research we won’t know if that’s justifiable or not.” What did The Lancet China study show? This study from Wuhan, China showed no statistically clinical benefit in Covid-19 patients in health improvement or mortality. However, the researchers tested a smaller number of patients – just over 200. They concluded their findings would require confirmation from larger studies. The study was stopped early by the data safety monitoring board because of difficulty recruiting patients. However, it is the first randomised controlled trial of the drug for Covid-19, which is considered the gold standard for evaluating the effectiveness of interventions. The results were accidentally published by the World Health Organization on its website earlier in April, before quickly being removed. Dr Phillip A Reece, a consultant to the pharmaceutical and biotechnology industry, said the findings from the US study were “clearly preliminary” and may have been precipitated by the accidental disclosure of the Chinese trial results. “This was disputed by Gilead,” Reece said. What should we take from all of this? Schneider-Futschik said comparing the results from the two studies is difficult. “There can be a lot of variables in the set-up of the study, and different stages of initiation of treatment,” she said. “Also, the Chinese study is incomplete as doctors could not access new patients during the lockdown. It might highly depend on when and at what stage of the infection patients receive the drug. We can say it is currently not clear who is benefitting from remdesivir. Is it helping patients who would have recovered anyway, recover quicker? Is remdesivir more beneficial for younger compared [with] older patients? At what stage of the infection does treatment yield the best outcomes? Hopefully, the global clinical study will answer these questions.” Professor of infectious diseases with the Australian National University Peter Collignon said what the drug had not been shown to do was stop people dying. “The death rate for this virus is terrible and we want it to come down,” he said. “This drug may have some benefits, but it’s clear from the data we have at this point, it’s not going to be the main answer.” Co-director of the Centre for Virus Research Professor Sarah Palmer said,“We cannot base our medical response on this one promising study.” “That said, this National Institute study has more than four times as many patients involved in the clinical trial, giving it greater power to determine the effectiveness of remdesivir. In the trial conducted in China it appears remdesivir was employed in combination with other therapies which may have complicated an assessment of remdesivir’s effectiveness.”