A combination of drugs commonly used to fight HIV, which also showed early promise in combating COVID-19, doesn't work.
Scientists in China wanted to see if lopinavir and ritonavir - sold together under the brand name Kaletra - was effective in treating the disease, which has now killed more than 11,000 people across the world in a matter of weeks.
There were reports from China, Thailand and Japan - where the first infections occurred - that some patients had responded well to lopinavir and ritonavir.
In order to find out whether it was a possible cure for the virus, researchers at the National Clinical Research Center for Respiratory Diseases in China conducted a trial on 199 COVID-19 patients. Ninety-nine were treated with lopinavir and ritonavir, and the others given standard care, for 14 days.
"Treatment with lopinavir-ritonavir was not associated with a difference from standard care in the time to clinical improvement," the study, published in the New England Journal of Medicine, found.
"Mortality at 28 days was similar in the lopinavir–ritonavir group and the standard-care group... The percentages of patients with detectable viral RNA at various time points were similar."
Treatment for 13 of the patients receiving lopinavir and ritonavir was stopped early due to adverse effects.
"In hospitalised adult patients with severe COVID-19, no benefit was observed with lopinavir–ritonavir treatment beyond standard care," the researchers concluded.
Another drug combination usually used to fight Ebola, chloroquine and remdesivir, is also being trialled. It was found to be effective against SARS, which is related to COVID-19, but never used as the outbreak was successfully contained.
But lopinavir and ritonavir were also found to be effective against SARS.
"We ultimately need to find a vaccine, which will be the most effective way of stopping the spread," said Prof Bruce Thompson, dean of health at Swinburne University.
"The vaccine needs to be developed and tested, going through the phases of a drug trial one through to three, which demonstrates that the drug is safe, does no harm and is efficacious. All other treatments may have antiviral components, which helps speeds up the process of getting well... We don’t have a one-size-fits-all drugs that fixes all viruses."
There have been dozens of clinical trials trying to find an effective drug.
"It is possible that some drugs could possibly 'cure' coronavirus but it is too early to tell," said John Curtin School of Medical Research's Gaetan Burgio.
"We at least know which ones don't 'cure' coronavirus such as anti HIV drugs. Incoming weeks will give us a better idea of which drugs will be suitable to treat or cure the infection."