Health care workers have been working on these challenges in a low-key way for a long time—and they have some answers that might be applicable to preventing the spread of Covid-19. The education part is easy, maybe: You tell people how important the action is—but to make it stick, you have to tell them not only over and over again, but in as many different ways as you can manage. “You have to continuously change and evolve your messaging and your tactics, because it becomes white noise very quickly,” Popescu says. “People become accustomed to the reminders, the flyers, the messages on their computers, and just don’t see them any more.”

You also can’t rely on people complying just because they know what to do. Colum Dunne, director of the Centre for Interventions in Infection, Inflammation, and Immunity at the University of Limerick, led a long-term study of how medical, nursing, and health students viewed hand hygiene as they went through their school and training and landed jobs in health care. “When they’re in college, their knowledge, attitudes, and awareness are all there. They are keen,” he says. “But as they stay in their career longer, they become less compliant. People are human: They’re busy, they have responsibilities, and they become jaded with the message.”

The experts acknowledge that people disagreeing with rules, or not feeling they apply, is a harder problem to crack. The health care industry tackled that, in part, by adopting a concept that originates in aviation: guaranteeing that anyone is allowed to speak up to prevent someone else from making a mistake, even if the person speaking up occupies a low position and the person doing wrong is highly placed. (The aviation version, known as crew resource management, originates from what is still history’s worst civilian air disaster: a runway collision between two Boeing 747s in 1977 on the island of Tenerife, which killed 583 people—and might have been avoided if one of the pilots had listened to warnings from a crew member who was junior to him.)

Cullen says social pressure—to prevent dangerous actions or to reinforce positive ones—can go a long way. After weeks of lockdown, she went out last week for her first post-Covid haircut. In the salon she visited in the suburbs of Chicago, everyone was masked, and at every station, there was a bottle of hand sanitizer. “And because it was visible, everyone realized it was important, and everyone used it,” Cullen says.

There are other aspects of hand hygiene campaigns that can show the post-Covid world what works, like having products that are pleasant to use—say, hand gels that are soothing instead of skin-chapping—and making them easy for people to access. (The hospital version of that is putting the hand gel dispensers near the opportunities for picking up or depositing superbugs: by the elevator, the telephone, and the doors to patient rooms.) Emphasizing empathy may work better than threatening people with risk: Health care workers may skip lathering up because they don’t feel at risk personally, but they may be willing to do it one more time if they understand they are risking the health of a patient who depends on them.

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But the most influential factor of all may also be the one that looks the bleakest for the US: role modeling provided by leaders. Health care organizations have had sustained success with hand hygiene campaigns when people at the top—chairpersons, presidents, CEOs—have taken it on as a personal crusade.

We can’t really tell how often government leaders wash their hands, but we have a good proxy for how supportive they are of Covid-19 public health measures: how much they support mask wearing. Of course, wearing a mask isn’t a foolproof defense against spreading the virus, but though the science is still evolving, it appears to lower the odds that an infected person will cough or breathe germs onto others. And even without rock-solid science, masks have become a signal of social cohesion, a visual shorthand for whether people take Covid-19 seriously.