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Coronavirus that triggered US epidemics arrived weeks later than thought, study finds

Coronavirus cases that set off Washington’s epidemic did not arrive until three weeks after the first case was confirmed on January 21, study finds

  • A Washington man was identified as the first US coronavirus case on January 21
  • The US restricted any non-US citizen from traveling into the US from China on February 2 
  • But a new analysis of the genetic evolution and spread of strains of coronavirus suggests the strain that became widespread in Washington arrived February 13 
  • Here’s how to help people impacted by Covid-19

The strain of coronavirus that triggered Washington’s epidemic likely did not arrive in the state until two weeks after President Donald Trump closed the US border to travelers from China, a new study suggests. 

Previous research suggested the strain of virus found in the first-ever US patient – a 34-year-old man in Snohomish County, diagnosed in January – quickly mutated into the iteration that infected scores more people in Washington. 

But new computer models made by University of Arizona scientists to replicate the way SARS-CoV-2 mutates could barely replicate that scenario. 

Instead, their research, posted to BioRXiv, but not yet in a peer-reviewed journal, suggests the form of the virus that spread in Washington arrived with Americans permitted to return to the US and funnelled through Seattle-Tacoma International Airport in the following weeks. 

During the intermittent weeks, travel to and from China was halted and the CDC produced its coronavirus test, but testing remained scattershot – a shortcoming that may have allowed the rapid spread of the disease in the US’s first outbreak. 

University of Arizona researchers found that the first US coronavirus case, known as W1 (bottom left) was a relative dead-end of transmission. Cases that led to more significant spread more likely arrived around February 13 (upper right)

‘Our analyses reveal an extended period of missed opportunity when intensive testing and contact tracing could have prevented SARS-CoV-2 from becoming established in the US and Europe,’ the researchers write.  

The case of the first identified US coronavirus patient – dubbed ‘WA1’ – was an exemplary one, from a public health standpoint. 

He was a young man, who returned via Sea-Tac International Airport on January 15, and had been closely monitoring the news and public health advisories. 

As soon as he developed symptoms, WA1 called his doctor before coming to a health care facility and getting tested. 

By January 19, the genome of the virus that had infected the man was sequenced and his contacts were swiftly identified and isolated. 

In the meantime, other Washington residents, of course, were not being tested, and thousands of Americans poured back to the US from China. 

And the new research suggests that it was with those travelers that the strain of coronavirus that spread through Washington came. 

All viruses mutate, but compared to others, we now know that SARS-CoV-2 evolves relatively slowly.

So when the ASU team simulated the mutation of the virus and thousands of transmissions. 

The researchers estimate that the strain that spread in Washington arrived from China's Hubei Province around February 13 (blue arrow) and from Europe to New York City around February 20 (yellow arrow)

The researchers estimate that the strain that spread in Washington arrived from China’s Hubei Province around February 13 (blue arrow) and from Europe to New York City around February 20 (yellow arrow)

They concluded that the strain from WA1 was a relatively dead-end one, discovering instead that the form of coronavirus that exploded in Washington arrived on or around February 13 – nearly two weeks after the travel ban for China was enacted on February 2. 

During the intervening weeks, the focus remained on the shutdown of travel from China. 

The Centers for Disease Control and Prevention (CDC) shipped its coronavirus test kits starting on February 5, but they trickled out to stats, had to be validated, and many turned out to be flawed. 

On a positive note, the researchers credit Washington’s response to the identification of WA1 – including contact tracing and social distancing – for keeping that first infection from spreading through the state immediately. 

On the other hand, they note that the response nationwide lagged in those same categories, leaving an open window for additional cases to enter the US and spread.