Coronavirus Briefing: What Happened Today

• The U.N. secretary general says the coronavirus poses the gravest threat to humanity since World War II.

• The federal government’s emergency stockpile of masks, gloves and gowns is nearly empty.

• Wimbledon, the oldest Grand Slam tennis tournament, is canceled for this year.

• Get the latest updates here, plus maps and full coverage.

Florida, a major holdout, issues a statewide stay-home order

Experts have long been eyeing Florida as a ticking time bomb in the coronavirus pandemic, because it has so many older residents (a quarter of the population is over 60), and it gets so many visitors from around the world (125 million annually), especially at this time of year.

Still, for weeks Gov. Ron DeSantis resisted calls for the kinds of sweeping statewide restrictions imposed elsewhere to slow the virus. Following President Trump’s lead, Mr. DeSantis tried to play down the pandemic, and to keep it at bay by discouraging visitors from hot spots like New York City and New Orleans.

But the state’s case count kept soaring, and images of its crowded beaches and spring-break partying drew mounting criticism. Frustrated local officials started imposing their own restrictions.

Mr. DeSantis finally changed his mind and issued a statewide stay-at-home order on Wednesday after a phone call with Mr. Trump. A day earlier, the White House had warned that 100,000 people or more might die in the U.S. before the pandemic ebbs, and on Sunday, Mr. Trump extended federal social-distancing guidelines through the end of April.

Developments from the scientific community

The urgency of the crisis has led to a new level of global scientific collaboration: Never have so many experts in so many countries focused simultaneously on one topic. What we know about the virus, and how to treat it, is expanding every day.

We are also learning a lot more about what we don’t know — like exactly who has the coronavirus. The Centers for Disease Control and Prevention now believes that as many as 25 percent of infected people may show no symptoms, significantly more than earlier estimates.

“This helps explain how rapidly this virus continues to spread across the country,” the agency’s director, Dr. Robert Redfield, told NPR on Tuesday.

Moreover, research out of China has found a high rate of false negatives: Around 30 percent of people who are tested and told they are negative may actually have the virus. It may be necessary to test twice to be sure.

In an article for The Times, Dr. Harlan Krumholz, a professor of medicine at Yale, suggests that “if you have had likely exposures, and symptoms suggest Covid-19 infection, you probably have it — even if your test is negative.”

Some good news in drug trials: A small study of 62 patients in China with mild cases showed promising results for the malaria drug hydroxychloroquine: patients who received it seemed to get over their symptoms faster.

And doctors around the world noticed that some Covid-19 patients seemed to experience “cytokine storms,” which is when their immune systems kept raging after the virus was defeated. That led them to try the drug tocilizumab, with early signs of success. The F.D.A. has approved testing in the U.S.

Zoom is the panopticon of the pandemic

The Zoom videoconferencing app has become a fixture in the lives of millions of Americans who are sheltering at home and are using it to connect to work, school, family, friends, worship services and digital happy hours. But recent reports are raising questions about the company’s security and privacy practices.

Motherboard reported last week that the Zoom iPhone app was sending user data to Facebook, even if the user didn’t have a Facebook account. (Zoom said it would remove the tracking software.)

The New York attorney general requested information from the company this week about its security practices, and took note of past security flaws “that could enable malicious third parties to, among other things, gain surreptitious access to consumer webcams.”

Another issue is “zoombombing” — when trolls hijack meetings to display graphic or disturbing images. The Boston office of the F.B.I. issued a warning about the practice this week after several Massachusetts schools reported that classes had been zoombombed with pornography, white-supremacist imagery and threatening language.

Jennifer St. Sume, a doctoral student in Washington, attended a virtual book club that lasted only 30 minutes before someone began blasting graphic content on the screen. “If I’m going to be asked to live in Zoom University or Zoom Tavern, then I want to know that it’s secure for everyone,” she said.

If you are hosting meetings, Zoom has tips and advice for keeping out crashers. Or you can switch to a competing service, like Google Hangouts, Facebook Messenger, Apple’s FaceTime or Marco Polo. And here’s our best advice for having a great video meeting.

The Times is now collecting county-by-county data on coronavirus infections and deaths, with a dedicated page for every state. You can find yours here.

Hot spots

• Iran, which has more than 47,000 cases and more than 3,000 deaths, said American-backed trade sanctions were making its outbreak worse and called on the United Nations to lift them.

• Twenty-eight Texas college students who traveled together to Mexico for spring break have now tested positive.

• President Rodrigo Duterte of the Philippines threatened to have the police and the military shoot people who protested the nation’s lockdown orders.

• The president of Brazil, Jair Bolsonaro, is the only major world leader continuing to question the need for social distancing measures. He said Brazilians could weather the pandemic because they could be dunked in raw sewage and “don’t catch a thing.”

What you can do

Keep walking. Even if it’s just around your living room. Taking 4,000 more steps a day — even slow leisurely steps — can significantly decrease your risk of dying early from heart disease, cancer and other causes, a recent study found.

Designate a set of “inside clothes.” Taking off shoes when you get home and changing into clothes you don’t wear outdoors is a good idea. When you do laundry, use gloves if you can, wipe down the laundry basket afterward and use the highest possible heat setting for the water.

Travel without going anywhere. Get vicarious vacation sensations on your TV with these 18 international thrillers, comedies, dramas and documentaries.

Get into gaming. If you’re not a video gamer, or it’s been a while since you have picked up a controller, our guide is full of tips for exploring the world of interactive entertainment. We even suggest the best games based on your interests.

Join our DealBook team for a conversation

The writers and editors behind DealBook will host a virtual discussion with Maggie Haberman, our White House correspondent, about the Trump administration’s response to the coronavirus crisis on Thursday at 11 a.m. Eastern time. R.S.V.P. to join them here.

What else we’re following

• The Trump administration decided against reopening the Affordable Care Act’s Healthcare.gov marketplaces to new customers, which would have made it easier for people who had recently lost jobs to obtain health insurance.

• From licking objects to coughing on people or willfully violating the six-foot rule, coronavirus agitators are acting out — and often facing harsh consequences.

• In the United States, people are hoarding toilet paper and clogging sewer systems with wipes of all kinds. Is it time for Americans to embrace the bidet?

• On Tech, a new Times newsletter, will explore how technology is transforming our lives and our world. Check out the first edition, which asks whether the internet has gotten nicer during the pandemic.

What you’re doing

I sent a Nintendo Switch Lite to my 80-year-old mother who must shelter alone. My teenage children taught their grandmother how to set it up and play via FaceTime and now keep her company while playing “Animal Crossing” virtually.

— Jeff F., Connecticut

Let us know how you’re dealing with the outbreak. Send us a response here, and we may feature it in an upcoming newsletter.

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Jonathan Wolfe and Tom Wright-Piersanti helped write today’s newsletter.

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