STEERING THE country through a pandemic demands a clear and consistent message from leaders. President Trump is right to want a calm and serious atmosphere in discussing it. But he and his administration have delivered mixed messages that only add to public confusion. They need to get their act together.

At his White House news conference Wednesday evening, Mr. Trump radiated optimism. He was careful to add caveats, but his overall message was that everything is going fine. “We’ve had tremendous success, tremendous success beyond what many people would have thought,” he said. “We’ve done, really, an extraordinary job.” “This is going to end. Hopefully it’ll be sooner than later.” “The risk to the American people remains very low.”

By contrast, Nancy Messonnier of the Centers for Disease Control and Prevention told reporters that “ultimately, we expect we will see community spread in the United States. It’s not a question of if this will happen, but when this will happen, and how many people in this country will have severe illnesses.” She added, “Disruptions to everyday life may be severe, but people might want to start thinking about that now.”

Who’s right? No one knows how severe the outbreak will become. But whom to believe? Mr. Trump declared that a vaccine was being “rapidly” developed. Anthony S. Fauci, director of the National Institute of Allergy and Infectious Diseases at the National Institutes of Health, cautioned that research and clinical trials will take a year or more and a vaccine won’t be ready for the current outbreak. Mr. Trump repeatedly returned to his newfound realization that influenza causes thousands of deaths a year, suggesting this new disease will not be as deadly. But no one knows that yet. The data from China, still tentative, suggests that covid-19 infection could be fatal to 1 in 7 people over 80 years old. That’s not a typical flu season. And there are no vaccines yet, unlike those widely in use to protect against flu.

“We’re totally prepared,” Mr. Trump declared, holding up a chart from the Global Health Security Index prepared by the Nuclear Threat Initiative and Johns Hopkins Center for Health Security, with the Economist Intelligence Unit, showing that the United States ranks first in health security. But this important study also found that national health security “is fundamentally weak around the world. No country is fully prepared for epidemics or pandemics and every country has important gaps to address.”

Individuals approach a danger such as the coronavirus with both reason and emotion. Both are understandable and even essential. But the mission for Mr. Trump and those working for him is to feed the reason, not the dread. That requires calmness but also candor.

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