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How COVID-19 Took Hold in North America and Europe

Posted on by Dr. Francis Collins

SARS-CoV-2 Tracking
Caption: SARS-CoV-2 introductions to U.S. and Europe. Credit: Modified from Worobey M, Science, 2020.

It was nearly 10 months ago on January 15 that a traveler returned home to the Seattle area after visiting family in Wuhan, China. A few days later, he started feeling poorly and became the first laboratory-confirmed case of coronavirus disease 2019 (COVID-19) in the United States. The rest is history.

However, new evidence published in the journal Science suggests that this first COVID-19 case on the West Coast didn’t snowball into the current epidemic. Instead, while public health officials in Washington state worked tirelessly and ultimately succeeded in containing its sustained transmission, the novel coronavirus slipped in via another individual about two weeks later, around the beginning of February.

COVID-19 is caused by the novel coronavirus SARS-CoV-2. Last winter, researchers sequenced the genetic material from the SARS-CoV-2 that was isolated from the returned Seattle traveler. While contact tracing didn’t identify any spread of this particular virus, dubbed WA1, questions arose when a genetically similar virus known as WA2 turned up in Washington state. Not long after, WA2-like viruses then appeared in California; British Columbia, Canada; and eventually 3,000 miles away in Connecticut. By mid-March, this WA2 cluster accounted for the vast majority—85 percent—of the cases in Washington state.

But was it possible that the WA2 cluster is a direct descendent of WA1? Did WA1 cause an unnoticed chain of transmission over several weeks, making the Seattle the epicenter of the outbreak in North America?

To answer those questions and others from around the globe, Michael Worobey, University of Arizona, Tucson, and his colleagues drew on multiple sources of information. These included data peretaining to viral genomes, airline passenger flow, and disease incidence in China’s Hubei Province and other places that likely would have influenced the probability that infected travelers were moving the virus around the globe. Based on all the evidence, the researchers simulated the outbreak more than 1,000 times on a computer over a two-month period, beginning on January 15 and assuming the epidemic started with WA1. And, not once did any of their simulated outbreaks match up to the actual genome data.

Those findings suggest to the researchers that the idea WA1 is responsible for all that came later is exceedingly unlikely. The evidence and simulations also appear to rule out the notion that the earliest cases in Washington state entered the United States by way of Canada. A deep dive into the data suggests a more likely scenario is that the outbreak was set off by one or more introductions of genetically similar viruses from China to the West Coast. Though we still don’t know exactly where, the Seattle area is the most likely site given the large number of WA2-like viruses sampled there.

Worobey’s team conducted a second analysis of the outbreak in Europe, and those simulations paint a similar picture to the one in the United States. The researchers conclude that the first known case of COVID-19 in Europe, arriving in Germany on January 20, led to a relatively small number of cases before being stamped out by aggressive testing and contact tracing efforts. That small, early outbreak probably didn’t spark the later one in Northern Italy, which eventually spread to the United States.

Their findings also show that the chain of transmission from China to Italy to New York City sparked outbreaks on the East Coast slightly later in February than those that spread from China directly to Washington state. It confirms that the Seattle outbreak was indeed the first, predating others on the East Coast and in California.

The findings in this report are yet another reminder of the value of integrating genome surveillance together with other sources of data when it comes to understanding, tracking, and containing the spread of COVID-19. They also show that swift and decisive public health measures to contain the virus worked when SARS-CoV-2 first entered the United States and Europe, and can now serve as models of containment.

Since the suffering and death from this pandemic continues in the United States, this historical reconstruction from early in 2020 is one more reminder that all of us have the opportunity and the responsibility to try to limit further spread. Wear your mask when you are outside the home; maintain physical distancing; wash your hands frequently; and don’t congregate indoors, where the risks are greatest. These lessons will enable us to better anticipate, prevent, and respond to additional outbreaks of COVID-19 or any other novel viruses that may arise in the future.


[1] The emergence of SARS-CoV-2 in Europe and North America. Worobey M, Pekar J, Larsen BB, Nelson MI, Hill V, Joy JB, Rambaut A, Suchard MA, Wertheim JO, Lemey P. Science. 2020 Sep 10:eabc8169 [Epub ahead of print]


Coronavirus (COVID-19) (NIH)

Michael Worobey (University of Arizona, Tucson)

NIH Support: National Institute of Allergy and Infectious Diseases; Fogarty International Center; National Library of Medicine


  • Sugathadasa R says:

    In my humble opinion the main reason for this pandemic to be so severe in Western Nations is mainly lack of Mindfulness. Mindful people are always in the present moment. They do not digress to dead past or the unborn future. Living in the present moment knowing how virulent this virus could be they take precautions to ensure it will not take hold. The precautions were already there, wearing face mask and keeping social distance. Images that I saw on western TV channels in beach and parks showed how people were hugging each other and not keeping distance.
    That was the cause for this effect of so many patients and deaths. Mindfulness can be developed with Mindfulness Meditation and that also increase the human capability to overcome these situations with more immunity.

    • Nancy JB Anderson says:

      I am from the US. Could you expand on your perspective, please? We are struggling with our need for emotional comfort and interaction and the isolation we are imposing and the scientific methods of wearing face coverings, hand washing and distancing. I have been looking into methods employed because it seems to lead to emotional as well as physical breakdown. I am considered an elder here and have noticed a severe reduction in compassion and rising fear and anger in our society that is very concerning to me.

      • Sugath Rajapakse says:

        I honestly do understand the situation you are talking of any how the US citizens are under so much pressure taking away their happiness. I know bit about US weather as I have travelled to USA since 1986, many times to Los Angeles, New York, Chicago, Atlanta, Dallas & Fort worth etc. on airline business meetings. When I went to Chicago in late 1995 I remember the temperature was – 30 degrees centigrade and hotel staff did not allow me to even get out of the front door to walk.

        So in such a situation, the time that people in north America or UK & Europe etc. to go out and and have good time outdoors is limited unlike in my country Sri Lanka where it is sunny 365 days of the year with temperature around 28 to 30 degrees most often. Yet you all have to face the reality of this virus infection causing immense trouble with over 15 million sick and more than 250,000 dead.

        But of course people can say like, “why not have a good time when we can, going out and enjoying with friends and relatives, go to the beaches etc. when it is warm”. Why do such thoughts arise? You see, we are of 6 agencies, eye, ear, tongue, nose, body and mind. these became agencies because as we grew up we uploaded all sorts of things, sights, sounds, taste, smell, touch and things with our 6 senses into our hard disk, the consciousness. Initially in early childhood these agencies were faculties, enabling us to see, hear, taste etc. But then we did not try to recognise them, and only as we grew up, we began to identify them with the illustrations of Name-Form in our consciousness. Suppose, a young child say an year old is given a rubber ball and told it is a ball. But the kid will not know as no identity stored and may try to bite thinking of food, or smell etc. and might recognise as something to play with but does not know it is a rubber ball.

        But as we keep growing and today with all these electronic media, social media, chat apps etc. we load trillions of things and ultimately become slaves to our 6 agencies of eye, ear ….. etc.

        But the beautiful this is there is a path, a way to overpower our 6 agencies. That is Mindfulness Meditation & Insight Meditation.

        Buddha said,

        “This mind is pure and bright, but get polluted with eternal stimuli. This the ones who have not heard Dharma and not trained do not know. Thus I say to them there is no mental development.”

        “This mind is pure and bright, but does not get polluted with external stimuli. This the ones who have heard Dharma and trained. Thus I say to them there is mental development”

        Let me give you a brief of my life. In 2004 while in office I had a heart attack. Taken to hospital and while in the ICU my heart stopped. It took 8 electric shocks to get it restarted and I was totally unconscious. I had slept for 18 hours and when I woke up, I had tubes inserted all over my body. The doctor said that I frightened them and it took hell of an effort to get my heart beating again. Heart had stopped for more than 50 seconds.

        Later I realised, that this is a godly messenger and to be heedful and that is when I started walking the path of Meditation and understanding the Dharma taught by Buddha. Gradually you begin to develop mindfulness and equanimity and that enable you to gradually overpower your 6 agencies. For example if for dinner say you have only bread and butter and jam, you will not yearn to go to restaurant but will be happy with what you have and eat. After all, you only know taste for say 10 minutes but food is in the stomach for may be 6 to 7 hours with no fuss. Same with other faculties. As you keep meditation and develop equanimity, you can face these situations.

        So my humble advice to you and all US citizens is to start developing mental wellness with Meditation for real happiness. In my youth, i watched many films with Elizabeth Taylor, Catherine Hepburn, Audrey Hepburn etc. and Sean Connery, Gregory Peck and many others. But when they were old, most would not be seen with crowds, and would hardly go out, why? because they cannot accept what the see in the mirror. But if they had done meditation and developed mindfulness and equanimity, they would not have bothered.

        In a way this Pandemic is reminding to most people all over the world who live as if they will never die, that one day we will die and thus do not procrastinate but be heedful.

  • Haresh Chunilal Patel says:

    Not recognizing the airborne transmission of COVID-19 is the cause of widespread infections. Countries which have recognized this mode have negligible infection rates without spending much money. Most underdeveloped countries have order of magnitude lower infection rates because they have few central HVAC systems and most of their facilities have open ventilation although they are not actually aware of the natural benefit.


    I’m curious about it spreading by Humane Waste and Waste Water here in WI we have Septic Companies spreading it on farm fields and growing crops. It’s been found in Waste waters tested and living there up to two weeks. Human wastes is being used as fertilizer untreated waste spread on farm fields and grow crops in it. We have large pits as holding tanks full of Human Poop Sitting in fields close to ground water, well water, rivers, and Lakes. Also steams that wildlife live in and are found sick and dying. How do we get test done to find Covid in our Waters I live in WI and our numbers are very High here Now and I read that Waste Water was tested in other States and it was found in it. I’m worried it makes me think it’s possible. Human Waste is a Biohazard and it is being spread all around us

  • Rod Krieger says:

    While studying the four fundamental forces in the beginning of my physics education, my professor wrote the word “gravity” on the blackboard and said “this word represents a lot of ignorance”. Every time I see the term “COVID-19” my mind takes me back to that moment.

  • arpi says:

    A bunch of thanks for sharing such valuable information with us …

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