Gilead shares fell about 4% in morning trading.
The late stage study of nearly 600 patients evaluated the safety and efficacy of 5- and 10-day treatment with remdesivir in addition to standard care for those with moderate COVID-19 – the disease caused by the new coronavirus – compared with standard care alone.
At day 11, around 76% of the patients in the 5-day treatment group showed improvement in clinical status versus 66% for standard care alone, Gilead said.
Around 70% of the patients who received remdesivir for 10 days showed improvement, “trending toward but not reaching statistical significance,” the drugmaker said.
Further study details than Gilead provided on Monday are needed to explain the difference in the two treatment groups, doctors and analysts said.
Remdesivir is being closely watched after the U.S. Food and Drug Administration granted emergency use authorization last month, citing results from a U.S. government study that showed the drug reduced hospitalization stays by 31%, or about four days, compared to a placebo.
Remdesivir, which previously failed as a treatment for Ebola, is designed to disable the mechanism by which certain viruses, including the new coronavirus, make copies of themselves and potentially overwhelm their host’s immune system.
Dr. Daniel McQuillen, an infectious disease specialist at Lahey Hospital & Medical Center in Burlington, Massachusetts, said it was difficult to draw a conclusion on why the patients on the shorter course outperformed those on the longer one until the full data is released.
The trial results “confirm our and others’ anecdotal experience,” McQuillen said in an email.
“The drug has promise in hospitalized patients treated early, when the illness is still in its viremic phase,” meaning the virus is circulating in a patient’s bloodstream.
Jefferies analyst Michael Yee said the improvements seen were only modest.
“This incrementally adds to a broader utilization of the drug into a more moderate population inside the hospital, but consensus already understands remdesivir is not a silver bullet,” Yee wrote in a research note.