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Coronavirus

The US just crossed a dangerous threshold

US infection has spread faster than in any other country

Today, Dr. Deborah Birx, the White House’s coronavirus response coordinator said something you should hear:

The only data that we all have [is that] the two areas that have moved through their curve [are] China and South Korea. […] Those were 8-10 week curves. Each state and each hot spot in the US will be its own curve because the seeds came in at different times.

So Washington State is on their curve, they’re about two weeks ahead of New York, and so each of these have to be done in a granular way to really understand where we are. It’s the charge of the President […] to really define those issues about where the virus is, where is it going, and what predictions we can make about where we are in that bell-shaped curve.

Dr. Deborah Birx, White House Press Conference, March 23, 2020

I think this is one of the most important dynamics to understand. There are two parts:

  1. Every infected city/area develops independently, tracing its own curve along the way
  2. Each of these curves started with a ‘seed’ individual at a specific time.

These two facts are important, because they unlock the ability to compare infections that happen at different places at different times. To do this, you need to define the beginning of a local infection and you need to record total cases over time.

Let’s call the beginning the day a region (country, state or city) reaches 100 cases. Now that you have “day zero”, you can plot cases on a common timeline: days since 100 infections. When you do, some startling (and terrifying) things become clear:

At Instagram, we called these ‘snail charts’. We’d use them to compare the growth of a product over time from day of launch (often we’d launch a product in one country before another)

State of the United States

The first conclusion to take in: the United States now has the fastest growing mature infection on record. What does this mean? Since infections start at different times, it’s hard to say which infection is ‘worst’. Presumably, an infection that goes from zero to 100,000 cases faster than another one is both qualitatively and quantitatively more troubling (mortality rates notwithstanding).

By the way, these lines don’t bend easily. When they do bend (China and Korea), it has taken draconian quarantines, mass surveillance and mass testing – none of which exist in the US. Even once these measures are in place, cases have taken over a week to flatten.

Looking at the chart and knowing the US has relatively mild measures, it’s not hard to conclude that cases will soar past China’s and end far higher. Only an act of god (or a more reasonable national lockdown of all transit and non-essential health, food and government business banned) will give the US a fighting chance. Any talk of reopening the economy soon will ensure this line stays straight, up, and to the right.

Flatten that Curve. Now.

Now with just four countries – but I’ve added dotted lines showing a hypothetical country that doubles every 1, 2, 3 and 7 days for reference.

I mentioned how hard it is to bend these curves. This is the second key lesson. There are only two ways these curves bend: reducing contacts between people and thus reducing transmission, or running out of people to infect. The key is to choose the former before being dealt the latter.

Take China: on January 23rd, they suspended travel and kept anyone from leaving Wuhan. Not everything went well. An estimated 300 thousand people left before the lockdown took place. In response, the government quarantined all of Hubei province’s cities by the 27th. By that point 56 million residents were under quarantine and every non-essential business was closed. The stunning fact about this all? At the moment of quarantine, there were a paltry 830 cases.

Let’s turn to Italy. After a series of cases linked to China, Italy’s cases grew quickly. On March 8th, when Italy had 7,375 cases, Prime Minister Giuseppe Conte quarantined all of Lombardy and 14 other northern provinces. Italy had nearly ten times the number of cases when China took similar action. And stories from the time show that there was little enforcement:

“There was no immediate disruption to air travel, either, with scheduled flights still departing and landing in Milan. A sign at Milan’s Linate airport assured passengers that regular service was continuing. Italy’s national carrier, Alitalia, said it would reduce the number of flights in and out of Milan.”

“Italy’s Coronavirus Lockdown Met with Confusion, Questions About Enfrorcement”
Margherita Stancati, WSJ.com

Realizing they were behind, Italy expanded this quarantine to the entire nation the following day, stopping all commercial activity, and finally closing all non-essential businesses on the 21st when the latest case count showed a towering 53,578 cases. Now, two weeks later, Italy’s cases have ballooned to 64,000. Sometimes early isn’t early enough. The good news is that for the second straight day the number of new cases in Italy has dropped. The prognosis is complicated, and I plan to write about that separately. But the lesson, if any, from Wuhan is that the most effective action is to lock down when infections are low.

Some US states have had a succession of increasingly restrictive lockdowns. First, San Francisco and surrounding counties mandated residents to shelter in place on March 16th – there were 472 cases. At the same time, New York Gov. Cuomo dismissed the idea of a shelter in place order:

“As a matter of fact, I’m going so far that I don’t even think you can do a state-wide policy.”

Gov. Andrew Cuomo, New York State Governor, CNN

Days later, with cases just topping 1000, California ordered residents statewide to shelter in place. Only then on the 20th, Gov. Cuomo announced a stay at home order – a euphemism for shelter in place. By then, cases in New York had reached 8,402. Today, not three days later, they passed 20,875.

I suspect history will show that the early action in California saved countless lives. At the same time, I worry the hesitation–if only for a few days–in New York might be one of the largest public policy mistakes of our generation.

US doesn’t have an infection, States do

The last conclusion, and one that I will revisit again in upcoming posts, is that it’s a mistake to analyze a country as a whole. After all, California has 40 million residents – Italy has 60M. The line between states and countries starts to blur. You can aggregate regions any way you want, but you will always get a clearer picture by analyzing the component parts. In this case, we have states – each of which has a very different trajectory.

The same chart, but now with states. This exercise can be repeated for regions of a country or even cities themselves.

Once you look at this chart, you can’t unsee New York’s line. Not only is it just as mature as Washington State (the state with the first infection, which arguably garnered most of the media attention for the last couple of weeks), but it has an order of magnitude more cases in the same time. New York is currently hugging the ‘doubles every two days’ line – which for a state of of nearly 20 million people should give you pause.

But don’t let the largest states get all your attention. The chart above shows that Michigan (1,328), New Jersey (2,860) and Illinois (1,285) have grown far more quickly in a shorter number of days. At the age each of those reached 1,000, New York was sitting in the hundreds.

Of course, this might be because of increased testing and therefore cases. It’s possible New York missed cases and is now catching up. Regardless, you should watch these states over the next week. They are all bigger and growing faster than New York at the same age and that doesn’t bode well.

When forecasting, you don’t always need a complicated model. Sometimes all you need to do is find similar situations and observe how they evolved. If they evolve in predictable ways, ask yourself: why is this time is any different? If you don’t have a good answer, you can surely expect more of the same.