Government clinical trial investigators changed the primary metric for measuring the success of Gilead’s experimental drug remdesivir as a coronavirus treatment two weeks before Anthony S. Fauci’s announcement that the drug would be the new “standard of care.” Instead of counting how many people taking the drug were kept alive on ventilators or died, among other measures, the National Institute of Allergy and Infectious Diseases said it would judge the drug primarily on a different outcome: how long it took surviving patients to recover. Death and other negative outcomes were moved to secondary measure status: They would still be tracked, but they would no longer be the key measure of remdesivir’s performance. The switch — which specialists said is unusual in major clinical trials but not unheard of — was publicly disclosed on the government’s clinicaltrials.gov website on April 16 but did not receive much attention at the time. The change reflects evolving scientific understanding of the fast-moving nature of the virus and uncertainties around how the lethal effects reveal themselves in patients, said NIAID, Gilead, and outside specialists. But the change also adds weight to the assessment of government and medical researchers that remdesivir is not a knockout drug that will change the trajectory of the coronavirus pandemic. On Friday, as expected, the Food and Drug Administration approved an emergency use authorization for the drug that will allow it to be prescribed for hospitalized patients infected with the coronavirus. The newly adopted criteria were a central feature of this week’s declaration by Fauci, NIAID’s director, that remdesivir reduced the time to recovery for surviving patients from 15 days to 11 days, a 31 percent improvement. “The data shows that remdesivir has a clear-cut, significant, positive effect in diminishing the time to recovery,” Fauci said as he sat in an Oval Office meeting with President Trump and other members of the president’s coronavirus task force. “It’s highly significant.” The difference in death rate, one of the original primary measures, was not statistically significant, Fauci said, showing only a marginal reduction from 11 percent in patients given a placebo to 8 percent in patients given remdesivir. Full release of the trial results would be made soon, Fauci said. Some medical research specialists questioned the change in the primary outcome measure of the trial, which had 1,063 patients. “I think that they thought they weren’t going to win, and they wanted to change it to something they could win on,” said Steven Nissen, a Cleveland Clinic cardiologist and expert clinical investigator who has led numerous drug trials. “I prefer the original outcome. It’s harder. It’s a more meaningful endpoint. “Getting out of the hospital early is useful,” he said, “but it’s not a game-changer.”