I’m a modeler of infectious diseases. Scientists in my group have been trying to understand the epidemic of Covid-19 almost since the beginning. 

But, when is the beginning?

One of the wonderful things about a life in science is that it is universal, and one makes friends and acquaintances around the world. 

There are moments in everyone’s life when you realize that the world has been changed forever, sometimes accompanied by the fact that one’s own knowledge is somehow special, that people who need to know haven’t been told yet, and that it is your burden to share the news. One day I received a call to inform me that my children’s beloved grandmother had died. When I entered the room to tell them, there was an innocence that I knew would be gone before I left it. I knew something that they did not. But, they needed to know.

I think for many scientists something similar happened in January or February of this year. But it wasn’t the children who needed to be told. It was the world.

Such a moment is personal, often deeply emotional. Recently, I reached out to a number of scientist friends around the planet — epidemiologists, population ecologists, mathematical biologists, people who might have been expected to have had such a moment — to ask what it was like. Here is what they wrote.

I was in the lab, starting to work on Covid-19, and this was when the first imported case in Japan was diagnosed as on 15 January. This was the second case in the world, and this was so strange to me. Chinese government said that there were only some 50 cases who were linked to wet market in Wuhan, but there were already two cases diagnosed outside China. I came to be sure that there are so many cases with human-to-human transmission, and this was the moment when I realized that this would be a pandemic.

— Hiroshi Nishiura, Kyoto

On January 23, I was at an NIH meeting related to potential pandemic pathogen research. Everyone had heard the news [that Wuhan had been locked down] and was beginning to discuss whether this would be a big deal. Over the next several weeks the concern turned more grave.

— Marc Lipsitch, Boston

Looking back, I’m astonished by how it was possible to maintain an illusion that that were not going to be severely affected by Covid-19 for so long. Of course, perhaps it is understandable in that it has hit modern society to a degree that other no other recent emerging disease had. For me the realization that Covid-19 was going to be a major changing force both globally and personally escalated over a couple of days. By late February I was carefully following news of case numbers increasing across Europe. Yet life went on as normal. During the first week of March I was attending a meeting in Heidelberg, Germany when I learned that there had been positive cases on our campus in Zürich. I didn’t worry about infection as due to other travel I had not been on campus before leaving for Germany but it did make Covid-19 a realized risk. On the train back to Zürich it felt like everyone was coughing.

— Anna-Liisa Laine, Zürich

I have led the JHU team responsible for tracking the novel coronavirus since January 22, when we first shared the CSSE Covid-19 dashboard publicly. Within a week it was already heavily circulating on social media platforms, getting picked up by mainstream media outlets, and had accrued over 1 billion hits. The popularity of the service led to a deluge of direct communications from users around the world, indicating a critical level of public concern. Further, while managing the data collection process, I was also acutely aware that the spread was exponential. In response to both the user demand, public engagement and the scale of the spread, by the end of January we had to make some strategic decisions about how to more efficiently manage the dashboard, both in terms of collecting the data, and the computational infrastructure supporting it. Together, these experiences made it virtually impossible to deny the severity of the situation at hand. 

— Lauren Gardner, Baltimore

Late January 2020, I realized Covid-19 had pandemic potential based on how fast it was already spreading in China and the fact that cases were starting to pop up in other countries.  I was teaching first-year calculus at that time.  I used the emerging case counts from the WHO to teach the students how to solve a simple epidemic. The students were amazed at the power of exponential growth.  Seven weeks later, that class was moved online as our province entered a state of emergency. 

— Chris Bauch, Waterloo

Early in the pandemic, we conducted two studies that revealed the enormity of the threat. The first study estimated the unseen prevalence and geographic radiation of SARS-CoV-2 prior to the January 23rd lockdown of Wuhan. Days prior to the lockdown, our analyses revealed that there were thousands of undetected cases in Wuhan and that the virus had already arrived unnoticed in dozens of cities throughout China. Our second study, though, was the real jaw dropper. In early February, we were still hoping that the strategies used to contain SARS in 2003 would work for SARS-CoV-2. On February 18th, based on an analysis of 450 Chinese case reports, we were shocked to find that SARS-CoV-2 spreads about twice as fast as SARS and often before symptoms even develop. I vividly remember where I was — at my kitchen table in Austin, Texas, late at night — when I had the sinking realization that this new virus had the makings for an unprecedented global threat — stealthy and deadly, but not quite deadly enough to galvanize the needed response.

— Lauren Myers, Austin

My moment was about the same time as yours [Stefan and I had briefly corresponded about cases appearing in Singapore] in mid February when imported cases started appearing here and the task force was formed and we were called in to work on it, then split teams and then working from home every days including every weekends.

— Stefan Ma, Singapore

I live in Nice, which is about ½ hour from the Italian border, and in early March we were receiving conflicting sanitary messages from France (“business as usual, things are under control”) and Italy (“entire cities on lockdown, thousands dying”). I teach a class about disease dynamics every year, so I understood rather clearly how the exponential dynamics would hit us and we prepared ourselves for what was to come. A few days later, we were on severe lockdown, for more than 2 months.

— Elodie Vercken, Nice

It must have been around February 20th. Our undergraduate students were studying for midterms, we were in the full swing of recruiting graduate students, and I had just made travel plans to attend an infectious disease conference in Seattle in April. When we started learning that asymptomatic transmission was possible for this new virus is when I first truly got worried. Things escalated quickly from there. By February 26th, the first non-travel US case had been detected and there was evidence that community transmission was ongoing. I remember one of the first things I did was reach out to my departmental colleagues who run (non-infectious disease) wet labs to alert them to think about contingency plans in case of closures. This was going to be bigger than any of us were prepared for.

— Shweta Bansal, Washington D.C.

I am currently working in the Sultanate of Oman.  We began to follow the news about the spread of the novel coronavirus.  Before it was officially announced by WHO as a pandemic, the rate of spread and geographic pattern alerted me and my family that it is going to be a real problem.  At that time (mid February – early March) we had a couple of American scientists visiting to assist us with management plans for nature parks. They started to panic and think about the possibility of being able to go back home if things get worse.  They started to find out ways to travel home and finally they were able to find places on the last flight out of Oman.

— Ali Hassan, Muscat

Not every outbreak turns into a pandemic. The early signals of H7N9 in 2013 looked a bit like COVID — pneumonia, potential human to human transmission, etc. — but that outbreak petered out. As I learned more and more about COVID in those early weeks of January — that this new epidemic was caused by a novel coronavirus, with sustained human-to-human transmission and asymptomatic or pre-symptomatic spread and the level of fear it was causing — I had a very bad feeling that this event would be difficult to contain and would be very severe.

— Nita Madhav, San Francisco

For me it was mid-January when it was obvious that was not a repeated spillover from a non-human source and the lack of genetic diversity meant it was a very recent origin. When the Imperial College report estimated the size of the epidemic in Wuhan to be in the 1000s based on exported cases, we knew this was a rapidly spreading human epidemic.

— Andrew Rambaut, Edinburgh

The first three cases of Covid-19 in the Czech Republic were reported on March 1. I thought this would be a good  opportunity to check how well the standard epidemiological models would fit the data. As it was quite clear  that the epidemics will not go away fast, I was unhappy that the conferences and foreign travel I planned were to be cancelled for this year and I would  not meet with my friends and colleagues. As all schools were swiftly closed on February 11,  I had to find out very quickly the best way to continue my teaching. I spent most of my time till the end of the semester recording video lectures for my courses and getting in touch with students. All in all, distant teaching took more time when compared with the usual contact teaching. Unfortunately, due to the recent increase in the number of positive cases in my country, it becomes clear that a similar situation will continue during the fall semester as well.

— Vlastimil Krivan, České Budějovice

For me the turning point happened on March 13. That Friday was our second day of class with my undergraduate Ecology course at the National University of Cuyo. We had mentioned to the students that there was a chance that we would have to move to some kind of virtual teaching. While we were doing an exercise on plant sampling methods that day in the garden outside our building, our deputy dean told me he thought that, at the rate of increase of the number of cases, towards mid-to-late April we would have to move to virtuality. That gave us at least a month to adjust to the new format. So I was shocked to hear in the news that evening that our university had decided to move fully to virtuality right away. We had to do a lot of creative problem solving. 

— Diego Vasquez, Mendoza

I’ve started to figure out that Covid-19 is going to be a big thing at the end of February, when I was doing a short-trip in France before going back to Mexico City. At that time, I realized that it was the pandemic that many of us have seen coming. So far, we had managed to (mostly) control the outbreaks caused by new viruses (Zika, avian flu, Ebola, West Nile, etc…), but it was clear that one day, one of them was going to spread throughout the world. Then, when I came back to Mexico City, people were definitely calmer than in France, but it was also clear for them that something big will come soon.

— Benjamin Roche, Mexico City

A couple of moments stand out to me. The first was in early February, when we were about to get on a plane for a family trip to Aspen with my then-6-month-old son, and it occurred to me that coronavirus infection might be a risk of air travel and that I didn’t know how bad it was for babies. I texted a pediatrician friend, who assured me that it wasn’t that bad for babies and that I shouldn’t worry about getting on that plane. The second moment was in early March, when we started to consider working from home (major local employers Apple and Google had recently bussed home employees mid-day and encouraged them to start working from home), and I told my lab they had the option to work from home if they felt more comfortable. Within a week, we had a county shelter-in-place order (the first in the country), and I had begun to realize that this was going to be like the 1918 influenza pandemic of our generation. That was the point at which my lab started thinking about how we could contribute to scientific and public understanding of the epidemic and control using mathematical modeling and online visualization tools.

— Erin Mordecai, Stanford

I have an email dated 27 Feb 2020 replying to a colleague: “My thoughts on Covid-19 – pandemic is very likely.” It was such a dry, intellectual statement, and I remember feeling incredulous that I could write those words with such ease and certainty while feeling total uncertainty and fear about how this could play out.

— Barbara Han, Millbrook

I remember driving home from work one evening in early March, having returned from what would be my last trip this year. That week was the week St. Jude stopped work-related travel and many of the places I had planned to go were cancelling on their own. I was working through my calendar mentally in my head and thinking about the conferences that would most likely be cancelled, plane tickets and hotels I needed to take care of, various other trips I should follow up on, and trying to determine how long the disruption would last. Thinking through all the issues that have now become familiar—vaccine development schedules, the ability of viruses to bounce back with any relaxation of vigilance—I had a growing sense of dread that things would be disrupted for a very long time. That started me thinking about much more important things than my work trips, like upcoming weddings, family reunions, “dream trips” that friends of mine had spent months or years planning, and I got overwhelmingly sad. It was the first time I think I fully realized there wasn’t going to be a way out. 

— Paul Thomas, Memphis

Two moments stand out for me. One was in the first week of February, when I saw early signals that there could be substantial transmission before people show symptoms. Despite hopes of rapid containment, it was clear contact tracing alone would struggle to contain outbreaks. The second moment was 19th February, when two deaths were reported in Iran, the first in the country. That meant there had likely been substantial undetected transmission. A couple of days later, a cluster of severe cases was reported in Lombardy, Italy, again suggested outbreaks had gone undetected. By that weekend, it was hard to see how Covid-19 outbreaks weren’t already underway in many other countries.

— Adam Kucharski, London

I feel like I was primed to worry about Covid-19 right from the start. For my entire career, I have been thinking about exponential growth. In early February 2020 I was worried. I was also primed to worry about Covid-19 because I live in Seattle. As the first cases started to spread in Seattle, I started drawing plots, day by day. It was very clear that case numbers were increasing exponentially. And while most people might not be worried about 8 cases or 10 cases, I was extrapolating those cases out, and it looked like hundreds, and then thousands, of cases were just on the horizon.  On Feb 15th, having looked at my exponential growth plots, I reached out to our financial planner.

— Daniel Promislow, Seattle

I began following news about Covid–19 fairly early – before the pandemic really kicked in and took off. Through January and February of this year, I kept watching the number of cases and countries grow, but it was kind of all at a distance. At the end of February I was due to travel to Kruger National Park in South Africa for a conference. While I did have some thoughts about the potential to get infected, I have to say that I still wasn’t particularly concerned. After the conference I travelled south to Swaziland with a colleague. Oddly enough, the moment when I realised that Covid-19 was going to change the world was when we crossed into Swaziland via a rural checkpoint. There were nurses there, taking temperatures and checking for signs of infection miles and miles from any major transportation hub. That’s when it hit me.

— Peter Thrall, Canberra

I got a briefing from the WHO and some Chinese colleagues as a member of the WHO Blueprint for R&D Scientific Advisory Group at 4 am PT on January 10. At that meeting the question came up about where the pandemic would spread. I immediately contacted Alex Vespignani about using GLEAM to examine this question. I think he was already working on it. Our first paper on global spread was submitted on January 20, 2020. That was before travel restrictions.

— Betz Halloran, Seattle

[Quotes have been edited for brevity. I thank all these friends for sharing these moments with me.]