Two trials aimed at testing one of the world’s most anticipated potential treatments for COVID-19 have been halted in China.

According to an update on clinicaltrials.gov, Gilead has been forced to stop a trial using remdesivir to treat severely ill coronavirus patients along with a study aimed a patients with milder symptoms due to low enrollment. Both trials were set up in China, where the number of coronavirus cases has dropped dramatically in recent weeks.

Originally developed to treat Ebola, remdesivir has now become a closely watched drug being trialed as a potential coronavirus treatment. Although some anecdotal evidence has emerged from patients who say the drug helped them recover from coronavirus, there are still no controlled studies demonstrating its efficacy. Earlier this month, the company released the results of a small-scale study showing that 68 percent of patients who took remdesivir had an improvement in oxygen-class support, but the study lacked a control group to compare the results to.

The drug is still being tested in several ongoing studies in the U.S. and EU.