President Trump did his best Sunday to reduce concern about the spread of the coronavirus in the United States. As he did during the first White House news briefing on the subject last month, he assured the country that younger Americans aren’t likely to die if they contract the virus.

“I think, very important, the young people and people of good health, and groups of people, just are not strongly affected,” Trump said. “Elderly people that are not well, or not well in certain respects, are, really, a very dangerous group. We have to watch them. We have to protect them very much.”

It’s true that the overall threat to younger Americans is lower. But it doesn’t follow that younger people can therefore ignore measures aimed at reducing the number of infections across the country.

There are two good reasons, captured in an effective poster created by the Baltimore Department of Health.

Some younger people may be at risk, even without knowing it. Others might transmit the virus without being aware they have it.

A quarter of those at risk are under younger than 60

The Kaiser Family Foundation released data Friday tallying the number of people in each state who are at higher risk should they be infected with the coronavirus and contract covid-19, the disease the virus causes. That includes two groups: those ages 60 and older, and those younger than 60 who have conditions that put them at higher risk.

Unsurprisingly, the states with the most individuals at higher risk are those with more people. California has 11.4 million residents who fall into one of the two categories above.

Importantly, about 4 in 10 Americans overall fall into one of those two categories. In West Virginia, about half of the population is at higher risk from the virus. It is also the only state in which no cases have been confirmed as of writing. D.C. has the lowest density of at-risk population.

As an aside, four states are scheduled to hold Democratic presidential primaries Tuesday. About 44 percent of the people in those states are at higher risk from the virus, including about 47 percent of Floridians.

Most of the at-risk Floridians are older than 60, as you might expect. But even there, a quarter of the at-risk adults in the state are younger than 60 and face higher risk from the virus because of health conditions.

Nationally, about 28 percent of those adults who are at higher risk are younger than 60.

These are estimates, but it demonstrates how Trump’s presentation might misrepresent the risk posed to younger Americans.

Younger people can spread the virus without knowing it

South Korea provides regular updates from its expansive testing on the virus. The distribution of cases in the country shows older people are more at risk of dying — but more confirmed cases are among those younger than 30.

Part of this may be that more people younger than 30 are being tested. But there’s also evidence that those who don’t exhibit symptoms of infection — including those with more robust immune systems — can nonetheless spread the virus.

“It appears that a Massachusetts coronavirus cluster with at least 82 cases was started by people who were not yet showing symptoms,” CNN reported over the weekend, “and more than half a dozen studies have shown that people without symptoms are causing substantial amounts of infection.”

Part of the problem may be that some people simply don’t exhibit many symptoms of infection. Miami Mayor Francis Suarez, 42, has tested positive for the virus, but he isn’t exhibiting any serious symptoms. Suarez is self-isolating, documenting his experience on social media.

In broad strokes, Trump’s assessment is accurate: The risk posed to younger Americans is lower than for older Americans. But the risk posed by younger Americans can be significant, if they contract the virus and unknowingly pass it to more vulnerable people. This is entirely the point of efforts to close restaurants, cancel sporting events and postpone concerts: keep even people who aren’t at much risk from contracting the virus so that those who are at risk are unlikely to contract it.

But it’s worth remembering those Kaiser numbers, too: Millions of younger Americans are themselves at higher risk. Some may not know it.