(Bloomberg) — Gilead Sciences Inc.’s drug remdesivir showed only a limited benefit in a large trial of more moderate patients with Covid-19, a result that may shift perceptions of the therapy already cleared for use in severe cases of the disease.In the phase 3 trial, a group of moderately ill, hospitalized patients getting the drug for five days showed a modest improvement compared to those getting the standard of care, the company said in a statement. But another group getting the drug for 10 days didn’t show a statistically significant improvement, which is likely to raise questions about why a longer course doesn’t help more. Severely ill patients weren’t included in the trial.The shares fell 2.8% to $75.68 at 9:36 a.m. in New York. They’re up 16% this year, largely on optimism around remdesivir. Gilead’s drug has become a symbol of efforts to reopen the economy and effectively treat patients stricken with the coronavirus. A working therapy would help reduce the risk for people who become sick, providing greater certainty to efforts to reopen economies around the globe.The clinical trial looked at hospitalized Covid-19 patients who had more moderate disease, with pneumonia but who didn’t have reduced oxygen levels at the beginning of the study. Patients were randomly assigned to get five days of remdesivir, 10 days of remdesivir, or the standard of care, and then evaluated on a 7-point scale.Overall, the differences were quite modest. The patents who received five days of remdesivir did best, with 76% improving by at least one point by day 11, compared to 66% who received standard of care.But confusingly, patients who stayed on remdesivir for 10 days did slightly worse than those who received five days of remdesivir, with only 70% of them improving at day 11. That difference wasn’t statistically significant compared to the standard of care group.“There seems to be growing evidence five-day treatment is as good or better than 10-day — somewhat curious given no clear side-effect liabilities and may seem counter-intuitive to the typical ‘more is better’ expectation,” said Brian Abrahams, an analyst with RBC Capital Markets. He said the difference could be caused by a less burdensome administration of the drug.The U.S. Food and Drug Administration cleared remdesivir under an emergency authorization on May 1, which has allowed hospitalized patients with severe cases of Covid-19 to begin using the therapy. The emergency approval followed early results from a large, placebo-controlled study run by the U.S. government that showed that patients getting remdesivir recovered faster than those that got a placebo.In the new trial, Gilead said there were no new safety risks identified across either treatment group. The company plans to submit the full data for publication in a peer-reviewed medical journal in coming weeks.(Updates with opening share price in the third paragraph)For more articles like this, please visit us at bloomberg.comSubscribe now to stay ahead with the most trusted business news source.©2020 Bloomberg L.P.