The results are from WHO's "Solidarity" trial, which evaluated the effects of four potential drug regimens, including remdesivir, hydroxychloroquine, anti-HIV drug combination lopinavir/ritonavir and interferon, in 11,266 adult patients across more than 30 countries. But doctors on the front lines of treating severe cases advise caution when interpreting the findings.
The WHO-led researchers say their trial, called the Solidarity trial, will continue.
It was the only drug with an Emergency Use Authorization for COVID-19 from the U.S. Food and Drug Administration. A preprint is available at medRxiv. In the hydroxychloroquine arm, the death rate ratio was 1.19 (104 deaths were reported in the active group of 947 patients as against 84 in the control group of 906); in the lopinavir arm, the death rate ratio was 1 (148 deaths in the active group of 1,399, as against 146 in the control group of 1,372); and in the interferon arm, the death rate ratio was 1.16 (243 deaths in the active group of 2,050; 216 in the control group of 2,050).
Remdesivir - initially developed by Gilead to treat Ebola - was also one of the drugs administered to President Donald Trump when he tested positive for COVID-19. Some received a combination of the drugs. Others got just one.
What about other Covid treatments?
The trial was able to generate conclusive evidence on the impact the drugs had on mortality, the need for ventilation, and duration of hospital stay.
"For each of these four re-purposed non-specific antivirals, several thousand patients have now been randomised in various trials".
"Poor-quality study design can not be fixed by a large sample size, no matter how large it is", Kalil told NBC News. Remdesivir is an antiviral medication. "Countries headed by women, such as Germany and New Zealand, have generally responded more effectively to the pandemic", the authors wrote.
Spinelli said it will be important to look at trials examining both remdesivir and dexamethasone to fully understand what recovery time, mortality and duration of infectiousness look like when both therapies are used together.
"Also, it said, "...no study drug appreciably reduced initiation of ventilation in those not already ventilated". It can not be prescribed in pill form for newly diagnosed patients to take at home.
The findings, one senior critical care medicine specialist said, imply that cheap steroids such as dexamethasone and methylprednisolone, also approved for Covid-19 are the "only things proven to reduce mortality".
"It's reasonable to expect that an antiviral has diminishing returns", said Cameron Wolfe, an infectious diseases expert and an associate professor of medicine at Duke University School of Medicine.
Women are more likely than men to consider COVID-19 a serious problem and to agree and comply with restrictions like staying home and wearing masks, according to a survey in March/April of more than 21,000 people in eight wealthy countries.
"The second phase is much more hyper-inflammatory", Wolfe said.
A preprint "was probably OK in January or February when we really had a public health emergency and wanted to disseminate critical information quickly", he said, adding, "We're moving to a space now in which changing standard of care by press release is a really unsafe precedent".
"The highest-quality data that we have published anywhere still says that remdesivir is effective", Wolfe said.