She said the vulnerability could be biological or behavioral. Women have more robust immune systems, Dr. Klein said. And more men smoke in higher numbers, and they are less likely to wash their hands, studies show.

“We don’t always understand why something is a risk factor, and we’re probably not going to be able to pinpoint one thing,” Dr. Klein said. “But it’s remarkable that we’re seeing this across such socially and culturally distinct countries as Italy and China. More needs to be made of this fact.”

On Friday, Dr. Deborah Birx, the coronavirus response coordinator for the White House, mentioned the gender disparity in deaths in Italy, but said the gender gap was “twice” as high in men at all ages. In fact, the report mentioned no deaths in people under 30 and very few deaths among men and women in their 40s and 50s. The heightened risk to men becomes apparent in their 50s, with the gender gap tapering off somewhat only at 90, probably because there are fewer men in this age group.

Over all, men represented 58 percent of 25,058 coronavirus cases in Italy, and 70 percent of the 1,697 deaths described in the report.