Coronavirus: Flattening the curve

Why taking it seriously is so important?

Reading time: 15 minutes

Flattening the curve

All epidemics start slowly. One or two infections per day slowly trickle into a regular stream and suddenly, out of nowhere, numbers of infected appear to go up by hundreds every day.

It also doesn't help that healthcare systems run lean. They're woefully underprepared to handle a sudden influx of hundreds of people in need of urgent medical help. This makes sense; there is no need to pay for equipment and staff that won't be in use 99.9% of the time.

So how is the sudden appearance of new, highly infections disease handled? The easiest way is to contain it. Isolate infected people from the general population. Find out who they've been in contact with and isolate them too. Halt the spread as much as possible, and disease will burn itself out as it runs out of new hosts to infect.

All attempts to contain COVID-19 failed.

A lot of ink was spilled over the past few weeks on another option; flattening the curve. The Washington Post, for example, ran an excellent article. If you haven't read it yet, it's short; read it.

To recap; the idea of flattening the curve is to slow down the spread of disease as much possible. This is turn reduces the number of active cases at any point in time, which reduces stress on the healthcare system. It buys us more time to develop a vaccine too.

One method for achieving this is through social distancing; isolate people from each other as much as possible, thus reducing the probability of disease transmission from one person to another.

That action is only as effective as long as people are willing to isolate themselves from other people. But people are people, we're hardwired to be social. So, not surprisingly, that's hard. But the alternative is much worse; the healthcare system will get overwhelmed. People will not get the medical attention they need - some will die as a result.

Let's demonstrate why. Down below is a small town (let's call it SimuTown) of about 5000 people. A single person is infected with the highly infective fictitious disease. It is not a deadly disease, but about 10% of cases require serious hospital treatment. With proper medical care, mortality is about 0.1%. However, if they don't get medical care, they will probably die. In this town, even in the middle of the outbreak, everyone just continues as if nothing is happening.

To start a simulation press on the ⏴button. You can pause it by pressing the same button. You can also reset this simulation by pressing the ⏹button. This will generate a new simulation, so each run should proceed differently from any previous runs.

You should get a mortality rate of somewhere around 8%.

What if that town started with social distancing as soon as possible? Public health care officials achieve this in real life by encouraging people to avoid public gatherings, closing schools, pubs, workplaces. Mass transit is limited. People are encouraged to work from home. In Italy, Wuhan and other places, a lockdown was imposed.

Not everyone can abide by this. Health care professionals still need to go to work. People still need supplies, so some shops remain open. Social order has to be maintained. So some social interactions will always take place.

The point is not to stop the disease from spreading completely, just slow it down enough.

Less More

Compare the ~8% mortality rate to this. This is only because of the speed it spread among the population, thus limiting the strain on the healthcare system. This allows sick people to get the medical attention they need. The only difference between this and the previous scenario is the degree and frequency of social interactions between people.

That's why everyone is encouraged to work from home. To cancel trips. To not hang out in public places. To wash your hands.

To see how this scenario would behave under different levels of social distancing reset it by pressing the ⏹button and change slider on the top right before starting simulation again by pressing the ⏴button.

Why fast response early is critical

Okay, Okay, of course, we'll take precautions, but why the hell are they closing my favorite pub, when we have only a few cases, dammit?! — Grumpy SimuTown resident

Let's take one step back.

Starting from initial exposure, all diseases progress through three stages:

Incubation period,

Acute/clinical period,

Recovery or death

For the SARS-CoV-2 virus, after the initial infection, there is about a 5-day incubation period, during which an infected person does not show any symptoms. During that period virus is multiplying in their bodies, however, it is not yet present in enough concentration to trigger an immune system response. They're essentially a walking time bomb, they just don't know it yet.

This means that at the onset of the epidemic, the number of all known cases is much smaller than the actual number of cases. The actual number of cases becomes known only later when infected people show symptoms at the end of the incubation period.

For any measure we take, we'll still see a rise in the number of infected people, at least for about a week. That is before we can even gauge how much of an effect measure had.

SARS-CoV-2 has another ugly trick that is accounted for in all scenarios you have seen so far. After people get sick, it takes about a week before the situation gets bad enough that people need to be put in intensive care.

So, if we act by the time our health care system starts to feel the heat, we acted too late.

Let's see what happens to SimuTown. It starts again with a single infected person, SimuTown behaving as if nothing is happening until the number of infected people reaches 5% (~280 people) of the population. After that, it will switch to a scenario with an even lower degree of social interaction than seen in the previous one.

For easier reference, people during their incubation period are shown as well. This was also taken into account in previous scenarios, but those people were shown as healthy. This is because, as of this writing, it is difficult to distinguish a healthy person from an infected person during the incubation period.

05.0%

Even when the town acted even more aggressively, the healthcare system still got swamped. And as a result, more people died, even though fewer people got infected.

To see how this scenario would behave given different thresholds reset it by pressing the ⏹button and change slider on the top right before starting simulation again by pressing the ⏴button.

Test, test, test

World Health Organisation has been screaming from the top of their lungs a simple message for the past few weeks; "Test! Test! Test!". And with a good reason.

All scenarios you've seen so far showed a full scale of an epidemic. It was immediately known when someone got infected. That's not, however, how it works in the real world.

We have to test people. Since it's impossible to test everyone all the time, we always have cases that are unknown to us. And those cases spread the disease amongst the population. So, whenever you see a number in news saying "X people test positive", multiply this by some factor, to get a real number of infected people.

The previous scenarios always showed an accurate extend of epidemic. When the number of infected exceeded a defined threshold, it immediately attempted to distance people. In default settings, results were not encouraging.

What if we don't have real-time information who is sick and who is not? How do we determine then when to take measures, and when it is still OK to go on as business-as-usual?

Let's put people of SimuTown trough another epidemic. This time we don't have accurate information on who is sick or not. We have to test them. So each day we pick 30 people at random and test them.

You saw a few times already how quickly diseases spread when we start only with one infected. But this time, we will enact strict measures only after 50 people test positive.

When this happens, the simulation will pause for a few seconds to show the full extent of the epidemic. After that, it will continue on full display as in previous scenarios.

50 C n

30 T n

What appears to be red and yellow dot here and there, when looked under the surface is a huge epidemic.

To try different parameters, as in the previous scenario, you can reset it by pressing the ⏹button and setting sliders to some other values before restarting it with the ⏴button. C n denotes the case threshold; that is how many positive tests need to be registered before measures are taken and T n denotes the number of tests done per day.

For how long?

By now it should be clear that social distancing should start as soon as possible, but for how long should it last? After all, businesses cannot remain closed indefinitely.

I'm not a policymaker. But there is a good rule of thumb to go with: as long as it takes.

Here's why; When restrictions are lifted too soon it just moves us at the beginning of an epidemic curve where cycle can repeat again.

Let's consider another scenario; the community takes the outbreak seriously. It does everything right. It imposes measures to flatten the curve. It contains the disease, the healthcare system is not swamped. Except they celebrate too fast and lift some restrictions way too soon and never impose such harsh restrictions again.

How soon were restrictions lifted? When there were only 5 infected people left.

For countries just at the beginning of the epidemic curve; strap yourself in, it will be a long ride. This thing won't blow over in just two weeks. Otherwise, if measures are lifted too soon, they might as well been imposed for nothing.

Final thoughts

With these scenarios, I hope to have shown you why acting fast matters. Why testing as much as possible matters. Why social distancing and isolation matter. What are the consequences for the community if we don't take it seriously.

These simulations should not be taken as an accurate representation of the spread of COVID-19 disease. Real-life is much more complicated than just a bunch of dots changing colors. But the same way the simulated disease spreads among the network of dots, so does Coronavirus spreads among the human social network.

We might never know if we overreacted. But by the time we discover we underreacted, it will be too late.

I'm not trying to spread panic. There already is too much of it on social networks. These simulations are not a prophecy. With proper care, These simulations will stay just that; simulations. As the image at the beginning of the article tells us; don't panic, but be careful!

If you can, stay the fuck home.

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