COVID-19 basics: Why it’s so much worse than the flu

by The Darwinian Doctor

In today’s post, I’ll explain in simple terms why COVID-19 is such a big threat, and why it’s so much worse than the flu.


  • I’m going to start covering the COVID-19 crisis
  • COVID-19 is about twice as infectious as the seasonal flu
  • It’s up to 80 times as deadly as the seasonal flu
  • It should be compared to the Spanish flu of 1918

I’m going to cover COVID-19

If you read my blog regularly, you’ll know that I usually write about personal finance and real estate, with a smattering of health, doctor life, home and gardening thrown in for good measure. But in just a few weeks, COVID-19 has altered our lives beyond recognition.  I feel a duty to cover this topic, both to explain the gravity of this virus, and chronicle the way it’s affecting our lives.

As a medical professional, I’ve seen the situation unfold before my eyes in lurid detail. I’ve watched with increasing horror as COVID-19 overwhelmed the medical systems first in China, then in Italy, and now in the United States.  All of a sudden, we’ve all gone from normal everyday life to various states of lockdown.  

I have the advantage of a medical degree to understand the deadly situation we’re in.  But I’ve heard some people who’ve said, “What’s the big deal? Isn’t it just like the flu?”

Well, COVID-19 is a huge deal, and unfortunately, it’s way worse than the regular seasonal flu.  

To explain why, I’m going to take just a few minutes to lay out some basics.  

What the heck is it? 

COVID-19 is the disease caused by a highly infectious virus in the family of Coronavirus (formally named SARS-CoV-2).  These viruses have little projections on their surface that give them a “crown” (or corona) appearance.  It’s in the same family as the viruses that caused SARS (SARS-associated coronavirus) and MERS (Middle East Respiratory Syndrome Coronavirus).  Here’s a picture:

The COVID-19 virus

Most people seem to be using the name of the disease (COVID-19) synonymously with the virus, so I’ll do that here as well for simplicity.

What’s the big deal?  

No one predicted that we’d have such a hard time with this virus.  COVID-19 is so bad because of a few things. First, humans have no immunity to this virus.  Second, we have no vaccine for this virus.  And finally, COVID-19 is virulent as hell.

It’s more infectious than the flu

This last part is really important to understand why COVID-19 is so bad.  Let’s compare it to the seasonal flu (influenza). If you get the flu, on average, you’ll infect 1.3 people.  So you can see why your doctors constantly annoy you to get your flu shot.  

Well, if you get COVID-19, you’ll infect 2-2.5 people!  This is way worse. (Source: World Health Organization. March 6, 2020)

Why is it this higher infection rate so much worse? Let me show you a little comparison I made. (If you think that these charts look quite similar at first glance, don’t be fooled.  Look at the scale on the left side.)

The Influenza chart shows how many new people are infected each day. On Day 90, 2620 new patients are infected, for a total of 11,350 people infected from Day 1.  This is pretty scary, and is one of the reasons why your doctor bugs you so often to get your seasonal flu shot.  

For the COVID-19 chart, I assumed that each patient infects just 2.25 other people, which is in the middle for transmission estimates.  On Day 90, 2,184,164 new people are infected. So when you add up all cases, 1 person with COVID-19 can infect 3,931,495 people in 90 days!

This is taking into account a 3 day serial interval for influenza and a 5 day serial interval for COVID-19.  By “serial interval,” I mean the time between initial exposure and transmission of the virus. This interval is well established for influenza, and thought to be 5-6 days for COVID-19.    

In plain terms, this means that every 5 days, each COVID-19 patient will infect approximately 2.25 more people, leading to exponential growth in cases.

If this enormous difference in infection potential between the flu and COVID-19 seems surprising to you, just remember that when it comes to exponential growth, little differences make huge changes to your outcome.  For finance folks, just think about the surprising difference to wealth generation that investment fund management fees make over a 30 year timeline.  

Symptoms are more severe than the flu

If COVID-19 just caused some sniffles, it wouldn’t matter if it was the most infectious virus in the world.  But it doesn’t. For 80% of people, it causes some level of fever, body aches, fatigue and a dry cough. But in 15% of people, it causes a severe lung infection requiring oxygen and hospitalization. In 5% of cases, the infection is so severe it requires intubation, which means a ventilator and breathing tube.  (Source: World Health Organization. March 6, 2020)

It’s this need for hospitalization and a ventilator that is causing such a crisis in terms of medical resources in hospitals across the world. I’ll go into this more in the future.

It’s more deadly than the flu

While the flu usually only kills 0.1% of the people it infects, COVID-19 kills somewhere between 0.3% (in Germany) to 8.4% of the infected (in Italy).  

So basically COVID-19 is somewhere between 3-84 times as deadly as the flu, depending on where you live.  There’s a lot of theories why the virus is so much more deadly in some countries versus others. We’ll touch on this later in more detail also. But certainly some of the difference is determined by the number of people screened for the virus and also access to medical care.

As of March 20, 2020, the US fatality rate seems to be about 1.5%


I sincerely hope that in just a few weeks, we’ll look back on this time of confusion and quarantine and sigh with relief that it’s all over.  But with COVID-19 now in every state, and suppression efforts that are piecemeal at best, I fear that the worst is yet to come. 

So to sum it all up, COVID-19 is more infectious than the flu and kills more of the people it infects.  It’s not at all like the regular seasonal flu. It’s much more like the Spanish flu of 1918, that infected a third of the world and killed 50 million people.  This was about 3% of the entire world population.

In the following days and weeks, I’ll chronicle the different ways the COVID-19 crisis has changed our lives. 


Please comment, share, and subscribe for more content. Please follow your state and city guidelines on social distancing and restrictions on gathering.

The COVID-19 pandemic is a fast and fluid situation. My research and statistics are up to date as of the publication date of this post.

More COVID-19 resources:

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4 years ago

OK, it isn’t just the flu, but so far total deaths are less than 40,000 and this has apparently already peaked in China. China today has almost as many people as the entire world did when the Spanish flu hit. So how can you compare 40,000 to 50 million when more people today may have already been exposed to the virus than even were alive in the Spanish flu era? In fact you’d have to have 40 million die in China alone to approximate the same impact and so far only 3,300 people have died in China. If it has peaked in China already then the idea that another 40 million will die there seems unlikely. I’m not a doctor, I’m an engineer but I do understand data and statistics and for this to even approximate something like the Spanish flu it will have to get well over one thousand times worse than it is today. Do you really think that is likely given the currently available data? Do you even think this will approach the normal flu toll of some 650,000 deaths worldwide?

4 years ago
Reply to  Steveark

Mortality rates coming out of China are almost certainly false. There are local reports of funeral homes getting thousands of funeral urns delivered. One funeral home got two separate shipments of 5000 urns in one day. There are also reports that China has stopped testing most elderly patients for Covid and decreasing Covid testing in general. So when the elderly die, it is not being reported as death secondary to Covid.

N McClendon
N McClendon
4 years ago


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