Not to nag, but I need you to take a look at this map if you're considering seeing family for the holidays. It's a color-coded guide to the danger level of Covid-19, organized by geography and crowd size (at the US county level). Next, you choose the venue where the meeting will take place. Then with the slider, you can pick an event size on the left, from 10 to 5,000 individuals, and watch the chance of at least one Covid-positive individual being there skyrocket the bigger the gathering gets. The probability is darn near 100 percent in some areas where the virus spreads out of reach, such as parts of the Dakotas, even if the gathering is only 10 people. Get much larger than 10 people, and the map spits out the odds that in certain areas you will share room with a sick person, calling it a virtual certainty.
We would always prefer not to gather public health experts for the holidays, but they recommend that if you go ahead with it the shindig should be done outside, with as few participants as possible, and everyone keeping their distance and wearing masks. But if you look at the map right now it reveals that there is no such thing as a perfectly safe way of collecting during the pandemic around the US. The risk right now, even with all those precautions, is enormous, particularly if you're in the Midwest or hosting someone coming from the Midwest. In Cook County (which includes Chicago), for example, the probability of a Covid-positive person attending a meeting of only 10 individuals is around 50 percent. That chance is a whopping 99 percent in Jones County, Iowa. There are counties remaining at 99% in North Dakota, South Dakota, and Kansas.
We highlight the fact that these kinds of regional-level threats have changed," says quantitative biologist Joshua Weitz of the Georgia Institute of Technology, co-author of a new paper describing the map system in Nature Human Behavior." It was south, south-east, in late summer. And the Northeast in late spring and early summer. So there have undoubtedly been regional changes. And right now in the Midwest plains and upper mountain area, the highest and most worrisome rates of spread are.
Learn all of our coverage of coronaviruses here.
By bringing in frequently updated Covid-19 case reports from The New York Times for each county, Weitz and his colleagues developed the map. That doesn't say the whole story, however because many more people are infected with the virus, but because they are asymptomatic and never get tested, they don't know it. So if you look at the chart again, you can see a choice for "ascertainment bias" on the left. Based on serological studies, that is, people who have tested positive for the antibodies that suggest that their immune systems have mounted a defense against Covid-19, even if they never felt sick, the researchers conclude that there are currently 10 times more cases than reported in the US. The rate may be lower in areas where testing is more commonly available, hence the choice to use an ascertainment bias of 5 on the map.
The map spits out incredibly alarming chances of you coming into contact with a Covid-positive individual at a meeting, even a relatively small one of 10 people, regardless of whether you turn between an ascertainment bias of 5 or 10. Tick up the scale of the case, and the risk grows larger and larger. Slide the scale of the crowd to 25, and you'll see swaths of the Midwest where the map shows a nearly 100 percent chance of Covid getting anyone at the party. Also in California, which has found more virus control performance, some counties show a 50 percent chance of 25 people gathering. Florida, which over the summer became a Covid-19 hot spot, is actually looking a little worse.
It is especially concerning that so many parts of the US are now high-risk areas because of the existence of holiday celebrations, which frequently bring together people who have traveled from various parts of the world, mixing young and old family members together. If infected, young people are more likely to be asymptomatic, and can pass the infection on to older relatives who are more likely to develop severe symptoms. Weitz says of holiday activities, "It's almost certainly going to be cross-generation." "And right now, that is one of our greatest worries. The theory is that an asymptomatic case within a certain population will then spread to an older person, with a greater likelihood that it will lead to a serious case of hospitalization, whether it is the return of students from universities and schools, or simply social mixing and events. So both of these are about patterns.
An interactive map's importance is that it provides a striking visualization of complex data that can be difficult to parse for the human brain. "People, especially when it comes to risk, are intuitively bad at interpreting statistics," says Benjamin Singer, a critical care physician and pulmonologist at Northwestern Medicine, who was not involved in the work. "And so I think any instrument that visualizes the data in a more intuitive way, and the one in the paper is quite good, I think it's a good thing" (In addition to the Georgia Tech project, several other efforts have turned out color-coded risk charts for exactly this reason.)
In this map, the danger so intuitively visualized is also supported by alarming new modeling, also published in Nature this week. Researchers obtained anonymized location data from the phones of nearly 100 million Americans and mapped how individuals during the pandemic traveled to 500,000 points of interest, locations such as restaurants, gyms, and cafes, and how long they lingered in those places. They also had data on square feet, because in these places they could measure the hourly density of occupants. They then calibrated a model, using estimates of reported cases and deaths in cities from The New York Times. They could consolidate data sets that correlate the movement of people with outbreaks of the disease with this information.
"We did not investigate events on our own, but investigated locations," says computer scientist Jure Leskovec of Stanford University, a co-author of the report. Leskovec and his colleagues found that 85 percent of expected infections are responsible for only 10 percent of points of interest in the Chicago area. "We see that there are these points of interest that really stand out where a large fraction of infections happen," he says. What do they have in common at these locations? As many Americans prepare to do for holiday celebrations, they pack people indoors, mostly for extended periods of time. (The scientists did not model movements between households, but rather how individuals moved from their homes to other points of interest, to be clear.)
For the distribution of Covid-19, Leskovec and his colleagues could then model new scenarios. "Under our model, the prediction is that if people do not stay at home or at a social distance, a third of the entire population will be infected in one month," Leskovec says. "And for instance, if you just reopened the restaurants at the same level as before the pandemic, about 6 percent of the population would get infected in a single month." In addition, their model suggested that if city officials decided to reopen restaurants only at 20 percent capacity, they would reduce new infections by more than 80 percent.
"These numbers are very striking, then," adds Leskovec. "And I think the conclusion is that we can only beat this virus together, socially distancing ourselves."
Hospitals are already filling up with energy in the US and even President-elect Joe Biden has warned that we're in for a dark dark winter. So do not nag, but maybe rethink the holiday party. They're definitely not doing it indoors and without masks. You should handle your family members outside your household as strangers, as Singer puts it, believing they may be contaminated and taking every precaution you can. Since this new map shows just how possible it is that even in relatively small groups, you will come into contact with someone who is infected but does not know it. It's very striking, looking at that map, that this is a real thing," says Singer." "Even if you meet someone who has taken standard precautions as a family member, it could still be true that around the Thanksgiving table they're infectious."
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