The antiviral drug remdesivir appeared to have an effect in American cruise passengers treated for the novel coronavirus in Japan, although data are limited, according to a doctor sent to Tokyo by the U.S. government.

Rear Adm. Richard Childs, an assistant surgeon general and lung specialist at the National Institutes of Health, said 14 Americans who contracted the virus on the Diamond Princess cruise ship and were treated at Japanese hospitals received the experimental drug from Gilead Sciences Inc.

Those 14 were “critically ill people and their average age is 75,” he said. “Many of them were probably going to die in a short amount of time, and two weeks later nobody has died and more than half of them have recovered. It’s just absolutely amazing.” But he cautioned, “It’s going to take us a while to figure out what the impact of the drug has been.”