COVID-19: at the Crossroads

Thursday, March 12

This post was written by Tornus (who has no professional qualifications but has an extensive amateur interest in epidemiology) and Dr Smartypants, who is a physician and infectious disease epidemiologist with extensive experience working at the CDC and public health departments. We have endeavored to provide accurate, concise, and actionable information here. However, the best source of information about COVID is the official CDC page. You should trust the CDC more than us (or anyone else).


In our previous piece we tried to convince you that COVID-19 is going to be devastating. In this piece, we want convince you it’s critically important to immediately start implementing strict social distancing measures.

Even though we still have a lot of questions about the clinical aspects of COVID-19, we know a great deal about how it’s going to spread. This understanding comes from studying the 1918 flu pandemic, mathematical modeling, and early data from the COVID-19 pandemic itself.

In this piece we’re going to discuss three things:

  • What is social distancing and why is it our most important tool?
  • Why should we start acting now?
  • Why is slowing down the pandemic so important?

The world is now in crisis and things are going to get much worse before they get better. People are going to die, and you are going to have to make some painful sacrifices in the coming months. That’s scary, and it’s OK if you need to take a little time to process it.

The message from the scientific community is clear: this is really happening and we know what we need to do.

What is social distancing?

Social distancing is the technical term for measures that slow the spread of a disease by reducing contact between individuals. It includes strategies like canceling public gatherings and closing schools. To understand why social distancing is so important for mitigating this pandemic, we need to understand two things about COVID-19.

1. The disease spreads primarily between people who are in close proximity to each other (within 6'). Secondarily, it can probably also spread via surfaces like doorknobs. Washing your hands and cleaning high-contact surfaces is important to help reduce those secondary forms of transmission, but won’t do anything to impact the main transmission vector.

2. Most people who get infected have a long initial period of being infectious with mild symptoms or no symptoms at all. It’s impossible to tell who’s infectious and who isn’t: if you’re within 6 feet of someone, they could be infecting you. And you could be infecting them, even if you don’t think you’re sick.

This means that social distancing has to be our main strategy for mitigating the pandemic. Washing your hands isn’t enough, and buying toilet paper won’t help at all. You need to spend much less time near other people.

Social distancing works

Extensive data show that social distancing is highly effective against diseases like COVID-19.

The most extreme case, of course, is China. Through draconian social distancing measures, China was able to rapidly pivot from an epidemic with an exponential growth curve to having almost no new daily cases. The long-term sustainability of China’s measures is questionable, but it’s an impressive demonstration of the power of social distancing.

For a more realistic look at what social distancing can achieve, let’s compare Japan and Italy. Both countries made significant mistakes early on, but Japan implemented considerably more stringent social distancing measures as well as more stringent hygiene measures. Those policies made a huge difference:

Japan has a population of 126 million people, 26% of whom are 65 or older. Their first known case was on January 16 and they now have 568 known cases, with 12 deaths.

Italy has a population of 60 million people, 23% of whom are 65 or older. Their first known case was on February 20 and they now have 10,149 known cases, with 631 deaths.

Despite having similar demographics, twice the population, and a first case that occurred 35 days earlier, Japan has experienced 50 times fewer deaths than Italy.

Social distancing works.

Time is of the essence

Do we really need to implement social distancing now, or can we wait until things get bad?

Epidemiologists like to talk about St. Louis and Philadelphia during the 1918 flu pandemic. Both cities experienced serious flu epidemics, but St Louis imposed severe social distancing measures 2 days after their first case, while Philadelphia waited 16 days.

St. Louis experienced 314 deaths / 100,000 population, while Philadelphia experienced 719: a two week delay doubled the death rate. COVID-19 spreads faster than flu, so waiting two weeks to implement social distancing would be even more disastrous in this case.

Oh, one more thing: the US had its first confirmed case of COVID-19 on January 21. That was 51 days ago.


You may have noticed that all the cool kids are using #flattenthecurve. What’s up with that?

Let’s take another look at St. Louis and Philadelphia. Because of social distancing, St. Louis had a peak death rate of 31 / 100,000 / week, compared to Philadelphia’s peak of 257 (8 times higher). A lower peak death rate means that the entire health care system is less overloaded. Remember what’s happening in Italy right now:

“My friends call me in tears because they see people dying in front of them and they con only offer some oxygen. Ortho and pathologists are being given a leaflet and sent to see patients on NIV. PLEASE STOP, READ THIS AGAIN AND THINK.”

When there are too many patients at one time, the healthcare system overloads and people start dying who could have been saved under normal circumstances. In the case of COVID-19, we can take a guess at how bad this might be. Under normal circumstances, case distribution looks something like this:

  • 80% of cases are “mild”
  • 15% of cases are “severe”
  • 5% of cases are “critical”
  • 1% of cases will die

But if the healthcare system is overloaded, everything changes. Critical patients (5%) will probably die without advanced medical intervention and even severe patients (15%) will be at grave risk. If that happens, the case fatality rate could easily go much higher than 1%.

Remember Tom Frieden’s worst-case estimate of 1.6 million US deaths? That’s based on a 1% case fatality rate. If we don’t slow the pandemic down, the actual number could be much higher.

What now?

COVID-19 is really scary. Something that seemed very distant and abstract to most of us just a few weeks ago has suddenly become very real. The good news is that although we can’t stop it from happening, we know exactly what we need to do to greatly reduce the impact.

Take a deep breath, and let’s do this.

Further reading

Coronavirus: Why You Must Act Now
This excellent piece goes into far more detail about why we need to act quickly and decisively to slow the pandemic.

Coronavirus containment in China
This is what we mean by “draconian social distancing methods”.

Jason Van Schoor: report from a Lombardy physician
“My friends call me in tears because they see people dying in front of them and they con only offer some oxygen. Ortho and pathologists are being given a leaflet and sent to see patients on NIV. PLEASE STOP, READ THIS AGAIN AND THINK.”

Silvia Stringhini: report from another Lombardy physician
“Cases are multiplying, we arrive at a rate of 15-20 admissions per day all for the same reason. The results of the swabs now come one after the other: positive, positive, positive. Suddenly the E.R. is collapsing.”

Think Global Health: Could Coronavirus Kill a Million Americans?
Written by the former head of the CDC, this piece calculates a plausible worst case scenario of 1.6 million American deaths.

WHO COVID-19 Situation Report - 51
WHO’s latest daily report on the pandemic.

Characteristics of and Important Lessons From the Coronavirus Disease 2019 (COVID-19) Outbreak in China
A preliminary technical analysis of the early outbreak.

Wikipedia: Demographics of Italy

Wikipedia: Demographics of Japan