Recent studies on possible cures for the coronavirus have shown mixed results, as researchers around the world race for a medical treatment to halt the pandemic.

Two-thirds of a group of 61 severely ill coronavirus patients saw their conditions improve after taking remdesivir, according to an analysis published Friday by the New England Journal of Medicine. The experimental drug developed by California-based Gilead Sciences Inc. began clinical trials last month, with results expected in the coming weeks.

The study does not provide details on other treatments the patients were given and does not provide a comparison to a control group, as is customary in clinical trials. The drug will likely need more clinical trials and studies to prove its efficacy in treating the virus.

“In studying remdesivir, the question is not just whether it is safe and effective against COVID-19 but in which patients it shows activity, how long should they receive treatment and at what stage of their disease would treatment be most beneficial," Daniel O’Day, Gilead’s chairman and CEO, said in a letter. “Many answers are needed, which is why we need multiple types of studies involving many types of patients.”

On the other hand, France’s drug-safety agency has found that anti-malarial drug hydroxychloroquine could have serious health impacts. A report released by the agency shows 43 cases of “heart incidents” tied to the drug.

“This initial assessment shows that the risks, in particular cardiovascular, associated with these treatments are very present and potentially increased in COVID-19 patients. Almost all of the declarations come from health establishments,” the agency said. “These drugs should only be used in hospitals, under close medical supervision.”

Trump has touted the drug as a “total game-changer” but top U.S. infectious diseases expert Dr. Anthony Fauci has been more cautious about the treatment. Doctors have said that it may take weeks or months to determine whether the drug is effective against the virus.

The coronavirus originated at an animal and seafood market in Wuhan, China and has since spread around the world. As of Sunday at 12:45 p.m. ET, there are over 1.8 million cases of coronavirus, with the number of deaths close to 111,000.