How the coronavirus settled in North America and Europe

The new study combines evolutionary genomics from coronavirus samples with computer-simulated infectious diseases and detailed travel records to reconstruct the spread of coronavirus in unprecedented detail around the world.

Published in journal ScienceThe results suggest a long period of time in which intensive testing and contact tracking missed opportunities that could have prevented SARS-CoV-2 from being established in North America and Europe.

The paper also challenged a proposal to link the earliest known cases of COVID-19 outbreaks on each continent in January to outbreaks detected weeks later, notifying public health responses, and COVID-. Zoonotic disease provides valuable insights to help predict and prevent 19 and other future outbreaks.

Michael Worobey, a researcher at the University of Arizona, led an interdisciplinary team of scientists from 13 research institutes, saying, “Our wish is how pandemics evolved in space and time around the world. It was to develop and apply a powerful new technology for clear analysis. ”In the United States, Belgium, Canada and the United Kingdom,“ Previously, science, social media and an unprecedented number of preprinted publications were still peer-reviewed. There were various possibilities while waiting for. “

The team conducted an analysis based on the following results Viral genome Sequence work started immediately after the virus was identified. These efforts have rapidly grown in scale and pace into an unprecedented global effort, producing tens of thousands of genomic sequences published in databases.

In contrast to the widespread story, researchers found that the first documented arrival of infected individuals traveling from China to the United States and Europe was not a snowman in the continental outbreak.

Instead, swift and definitive measures aimed at tracking and containing their initial invasion of the virus should be successful and serve as a model response for government and public health agencies to direct future actions and policies. The authors of the study conclude that there is.

How the virus arrived in the United States and Europe

Chinese citizens flew from Wuhan, China to Seattle on January 15, the first patient in the United States to be infected with a new coronavirus, and the SARS-CoV-2 genome was sequenced for the first time. It was. This patient was called “WA1”. It was six weeks later that some more cases were detected in Washington State.

“And while all that time goes by, everyone is wondering what’s going on in the dark. “Warrobby said. “I hope we’re okay. I hope there are no other cases. Then there are more cases in Washington from Seattle’s featured community virus sampling program, and they are genetically It turns out that it is very similar to the WA1 virus. “

Worobey and his collaborators tested a general hypothesis suggesting that patient WA1 established a transmission cluster that was undetected for 6 weeks. Genomes sampled in February and March share similarities with WA1, but they have the following WA1 idea: Outbreak They determined that they were very unlikely. Researchers’ findings indicate that the jump from China to the United States is likely to have occurred on or around February 1.

The result is also the earliest outbreak in the United States, an outbreak that was initiated indirectly by the spread of the virus from China to British Columbia, just north of Washington, and then from Canada to British Columbia. Multiple US SARS-CoV-2 genomes published by the State Center for Disease Control appear to be the ancestors of a variant of the virus sampled in Washington, strongly suggesting the origin of the US epidemic in Canada. I am. However, this study revealed sequence errors in these genomes and ruled out this scenario.

Instead, this new study suggests a direct source from the United States just around the time the US government enforced a travel ban on travelers from China in early February. Even after the ban came into effect, the nationality of the outbreak “indexcase” in the United States is unclear, as tens of thousands of US citizens and visa holders have traveled from China to the United States.

A similar scenario shows the first known introduction of the coronavirus into Europe. On January 20, an employee of an automotive supply company in Bavaria, Germany, jumped into a business meeting from Shanghai, China, unknowingly carrying the virus and eventually infecting 16 colleagues. In that case, the study concludes that rapid testing and an impressive response to quarantine could prevent the spread of the outbreak. Contrary to speculation, this German outbreak was not the cause of the outbreak in Northern Italy, but eventually spread throughout Europe, and eventually in New York City and the rest of the United States.

The authors also ignited an infectious disease cluster on the East Coast, a little later in February than the China-to-Italy spread route of the virus that established an outbreak in Washington from China to the United States. It shows that you did. The Washington State Epidemic Cluster preyed on a small cluster of community epidemics in California in February, the earliest in North America.

Initial containment work

The authors reported symptoms to health authorities, timely self-isolated, and outbreaks of these in Germany and the Seattle area through intensive interventions including trials, contact tracking, quarantine measures, and high compliance of infected individuals. Said that it prevented. January.

“We believe that these measures were able to counteract the first spark and prevent further expansion into the community,” Worobey said. “What this tells us is that the measures taken in those cases are very effective and serve as a blueprint for future responses to emerging diseases that may escalate into a global pandemic. must.”

To reconstruct the pandemic deployment, scientists ran a computer program that carefully simulated the epidemiology and evolution of the virus, how SARS-CoV-2 spreads and mutates over time.

“This allowed us to re-run the tape about how the epidemic evolved over and over again, matching the scenarios that appear in the simulation with the patterns that we actually see,” Worobey said. It was.

“In the case of Washington,” what if the patient WA1 who arrived in the United States on January 15 actually caused the outbreak? “Well, if he did, you would repeat the epidemic over and over again. Do you get the pattern we see when we run, sample infected patients from the epidemic, and evolve the virus that way? The answer was no. “

“If you seed that early Italian outbreak with a German outbreak, do you see the patterns you get from evolutionary data? And the answer is still no,” he said.

“By re-simulating the introduction of SARS-CoV-2 in the United States and Europe, it is highly unlikely that the first documented virus introduction into these locales will lead to a productive infected cluster. “, Said co-author Joel Wertheim. “Molecular epidemiological analysis at the University of California, San Diego is very powerful for revealing SARS-CoV-2 infection patterns.”

We then combined other methods with hypothetical epidemic data to obtain very detailed and quantitative results.

“The basis of this work is a new tool that combines detailed travel history information and phylogenetics, a kind of” house “that shows how the different genomes of viruses sampled from infected individuals are interrelated. We will create a genealogy, “said co-author Mark Schard. Of the University of California, Los Angeles.

“Our research shows that successful early intervention and detection can have a significant impact on both pandemic prevention and post-progression control,” says Worobey. “In the end, the epidemic slipped through, but there was an early victory to show progress. Comprehensive testing and case identification is a powerful weapon.”