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Coronavirus Disease 2019

The Shocking Numbers Behind the Novel Coronavirus Pandemic

Understand where the math could lead, and you'll know why we must stay home.

As the novel coronavirus, also known as SARS-CoV-2, spreads across the world, many people have dismissed the threat, likening it to seasonal flu. In fact, early reports indicated that most people have mild cases, and some are asymptomatic. Plus, even after the World Health Organization declared this a pandemic, most people didn’t know someone who’d come down with it.

Apathy was common, due to early observations that about 85% of infected people only experienced mild symptoms, with some experiencing no symptoms at all. Plus, it appeared that the elderly and people with underlying conditions had higher death rates (as in, “not me”) while the vast majority of younger, healthier people recovered easily (“that’ll be me).

Now that newer data shows closer to 58% having mild or asymptomatic cases and a significant number of younger adults becoming critically ill and sometimes dying, past reports of people ignoring social distancing advice and resisting “stay at home” orders can be seen in a whole new light.

Many have asked, “What’s the big deal? Aren’t we overreacting?” Unfortunately, I think the answer is no.

This virus, which causes the disease named COVID-19, could be more contagious, and more deadly, than the seasonal flu. To better understand this, let's take a look at the math.

Measuring contagiousness

The contagiousness of a disease is described by its “reproduction rate” or the average number of people infected by one infectious person in a population without immunity. You might also hear this number referred to as the R0 (R naught) value. When the R0 value is less than 1, the disease doesn’t become an epidemic.

What are the reproduction rates of other similar diseases? For comparison, a 2014 review of 121 studies laid out the reproduction rate estimates of various pandemic, seasonal, and novel influenzas that have occurred over the years.

Seasonal influenza reproduction rates range from 1.19 to 1.37, with a median of 1.28. This means that for every 100 people who have the flu, the central tendency is for them to collectively pass it on to approximately 128 more people. Those 128 people then pass it on to approximately 164 more people, who pass it on to about another 210 people, and so on.

Depending on the incubation period (how long it takes for someone who is exposed to become infected and contagious) these numbers can steadily add up. For example, one 2011 study estimated that seasonal influenza infects approximately 9% of the world’s population annually. Today, the World Health Organization (WHO) estimates the annual number of seasonal influenza infections globally could be as high as 1 billion, including between 300,000 and half a million deaths, depending on the year.

To put this rate into context, let’s look at the 1918-19 influenza, which the CDC once called "the most severe pandemic in recent history." Depending on the data and modeling used, the reproduction rate is estimated to be in the range of 1.47 – 2.27. Research using morbidity data offers a broader range of 1.2 to 3 in the community, and 2.1 to 7.5 in confined settings. The median reproduction rate was somewhere between 2 and 4.

While the difference between seasonal flu (1.28) and 1918 influenza (say about 3) may seem small, the difference in the percentage of people affected is substantial. While seasonal flu infected around 9%, the 1918 influenza infected 33% of the world’s population.

How does the current novel coronavirus SARS-CoV-2 compare? There is a lot we don’t know, but as researchers start to collect data, preliminary results from 12 studies in various countries, including China, showed that its reproduction rate ranged from 1.4 to 6.49, the median 2.79. Transmission could vary in different locations due to many factors, perhaps including population density, demographics, air temperature, public health measures, and test availability and administration.

This coronavirus also transmits very early, before the infected person shows symptoms. A recent study also points to evidence that many undocumented cases of COVID-19 and asymptomatic cases could explain the rapid spread, though there is some evidence that mild cases are not as infectious.

And as testing becomes more widespread and the numbers have become available, researchers are verifying that the reproduction rate may eventually show itself to be between 2 and 3. If the reproduction rate does approach that level, SARS-CoV-2 would be more contagious than seasonal flu, and possibly on par with the 1918 influenza pandemic.

Even if the reproduction rate turns out to be closer to 2, that means that its spread would be exponential to the power of 2 — or new cases and deaths would double within every unit of time. If the rate gets closer to 3, the spread is exponential to the power of 3, meaning the number of new cases and deaths would triple at every turn.

What does exponential spread look like?

Compared to the seasonal influenza rate of every 100 people infecting 128 people, the potential SARS-CoV-2 rate of 2-3 means that every 100 people will infect 200-300 people, who in turn will infect 400-900 people, who in turn will infect 800-2,700 people, and so on.

What's the difference? After just 3 cycles of seasonal flu spread, starting with those first 100 people, there might be a total of approximately 500 infected, compared to as many as 3,900 infected with COVID-19 in about the same period of time. And even if the reproduction rate of SARS-CoV-2 ends up being closer to 2, that’s a total of 1,400 people infected after just 3 cycles.

Also, if each cycle takes a week to complete (as in, the average incubation period between exposure and being infected and contagious), during the twentieth week, 14,000 people could become newly infected with seasonal flu. But during that same week, there could be over one million new cases of COVID-19; and over two million cases during week 21. If the death toll ever rises past 1 million, and the number of deaths keep doubling every week, after 10 more weeks, the death toll would exceed one billion.

These are frightening numbers, but such is the nature of exponential growth. And that's why it's imperative that we try to stop it. But how? Without widespread testing to isolate the contagious, our only option is to implement strict social /physical distancing orders.

The Course of COVID-19

In one early study of hospitalized patients in Wuhan, China, 26% required intensive care and 4% died. In another study, 32% required intensive care and 15% died. Both of these studies raised concerns about the severity of this disease, the death toll, and the likelihood of overwhelming health care systems.

Of equal concern is the lag time between onset of symptoms and various outcomes. As of March 5, 2020, data collected by the World Health Organization (WHO) showed that the median time from symptom onset to confirmation of pneumonia was 5 days. The median time from onset to intensive care (ICU) was 11 days, and the median time from ICU admission to death was 7 days. Therefore, the median lag from pneumonia diagnosis to death was 13 days. And from onset to death, the median was 18 days.

So when public health officials in your area are becoming alarmed by the rising number of people showing symptoms, it’s because they are bracing themselves for the coming onslaught of hospitalizations, ICU admissions, deaths, and the projected strain on medical resources.

Death rates

Seasonal flu causes an annual average of 36,000 deaths in the U.S., which is shocking, but the total death rate for the 1918 influenza was almost 19 times higher. Fortunately, 100 years later, we have more sophisticated medical knowledge, treatments, research, and technology, which can save more lives. But COVID-19 could be more deadly than seasonal flu. if COVID-19 is allowed to run rampant (without social/physical distancing in place) there will be shortages of hospital beds, equipment, and medical staff, making this virus even more devastating.

But experts point out that if we can avoid the exponential spike in cases, we can avoid overwhelming our health care systems. By practicing social distancing and abiding by stay-at-home laws, we might be able to reduce the reproduction rate and flatten the curve, so that while millions of people will eventually be infected by SARS-CoV-2, it won’t happen all at once, forcing doctors to perform triage, basically deciding who will get intensive care and who won’t.

Now that you see where the math could lead — in terms of reproduction rates and exponential growth — do you see the vital importance of flattening the curve and the necessity of social distancing?

It’s imperative that we stay at home. The life you save may be your own. Or somebody’s partner. Or somebody’s mama.

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