Coronavirus

It’s Not Whether You Were Exposed to the Coronavirus. It’s How Much.

When experts recommend wearing masks, staying at least six feet away from others, washing your hands frequently and avoiding crowded spaces, what they’re really saying is: Try to minimize the amount of virus you encounter.

A few viral particles cannot make you sick — the immune system would vanquish the intruders before they could. But how much virus is needed for an infection to take root? What is the minimum effective dose?

A precise answer is impossible, because it’s difficult to capture the moment of infection. Scientists are studying ferrets, hamsters and mice for clues but, of course, it wouldn’t be ethical for scientists to expose people to different doses of the coronavirus, as they do with milder cold viruses.

“The truth is, we really just don’t know,” said Angela Rasmussen, a virologist at Columbia University in New York. “I don’t think we can make anything better than an educated

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Coronavirus Epidemics Began Later Than Believed, Study Concludes

The first confirmed coronavirus infections in Europe and the United States, discovered in January, did not ignite the epidemics that followed, according to a close analysis of hundreds of viral genomes.

Instead, the outbreaks plaguing much of the West began weeks later, the study concluded. The revised timeline may clarify nagging ambiguities about the arrival of the pandemic.

For example, while President Trump has frequently claimed that a ban on travelers from China prevented the epidemic from becoming much worse, the new data suggest that the virus that started Washington State’s epidemic arrived roughly two weeks after the ban was imposed on Feb. 2.

And the authors argue that the relatively late emergence of the outbreak means that more lives could have been saved by early action, such as testing and contact tracing.

The new analysis is not the last word. Scientific understanding of the coronavirus is evolving almost daily,

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Trump Administration Coronavirus Testing Strategy Draws Concerns: ‘This Isn’t the Hunger Games’

The Trump administration’s new testing strategy, released Sunday to Congress, holds individual states responsible for planning and carrying out all coronavirus testing, while planning to provide some supplies needed for the tests.

The proposal also says existing testing capacity, if properly targeted, is sufficient to contain the outbreak. But epidemiologists say that amount of testing is orders of magnitude lower than many of them believe the country needs.

“For months, it was a tennis game, it was going back and forth between the feds and the states, and it’s now landed with the states,” said Scott Becker, executive director of the Association of Public Health Laboratories.

Mr. Becker noted that the

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Here’s How Wuhan Tested 6.5 Million for Coronavirus in Days

In Wuhan, medical workers armed with coronavirus test swabs scoured construction sites and markets to look for itinerant workers while others made house calls to reach older residents and people with disabilities. Officials aired announcements over loudspeakers urging people to sign up for their own good.

“Our community was checked in a day,” said Wang Yuan, a 32-year-old resident who lined up under red tents near her home and had her throat swabbed by medical workers wearing protective suits and face shields. She expected to get her results within two to four days.

While other governments have struggled to provide testing for their populations

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