Saturday, April 25, 2020

Past Pandemics

Credit: National Museum of Health and Medicine, public domain, source.

How does the current COVID-19 pandemic compare to past pandemics? Let's take a look.

The Black Death (14th century)

The Black Death was the worst pandemic in recorded history, resulting in 75-200 million deaths worldwide. Europe was particularly hard hit, losing 30-60% of its population. The pandemic peaked in Europe from 1347 to 1351. (Wikipedia) For this post I am using 100 million deaths and a world population of 400 million, for a death rate of 25%.

The disease of the Black Death pandemic was the plague. It is caused by a bacterium carried by fleas living on rats. Transmission is mainly by flea bites or handling infected animals, and secondarily through the air from the coughing of infected individuals.

Influenza Pandemic of 1918

The influenza pandemic of 1918 killed an estimated 50 million people worldwide (National Archives). Other estimates of the death toll range from 17 to 100 million people worldwide and 500,000 to 850,000 in the U.S. (Wikipedia). For this post I am using 50 million deaths worldwide and 675,000 in the U.S.

The pandemic occurred in waves. The first wave was in early 1918 and was relatively mild. The second, deadly, wave occurred in the fall of 1918 as World War I was ending. Lesser outbreaks continued into 1920.

While plague is caused by a bacterium, influenza (aka "the flu") is caused by a virus. There are many different influenza viruses. The 1918 flu pandemic was caused by the H1N1 influenza virus. Transmission of the flu is mainly through the air.

The photo above shows patients in an emergency hospital at Camp Funston, part of Fort Riley, Kansas, in the midst of the 1918 influenza pandemic. The photo is part of the Otis Historical Archives at the National Museum of Health and Medicine.

The influenza pandemic of 1918 is sometimes called the Spanish flu, but this is a misnomer as explained here.

Influenza Pandemics Since 1918

The U.S. Centers for Disease Control and Prevention (CDC) lists three smaller influenza pandemics since 1918 (source):
  • 1957 influenza pandemic, also called the Asian flu (H2N2 virus) – estimated deaths 1.1 million worldwide; 116,000 in the U.S.
  • 1968 influenza pandemic, also called the Hong Kong flu (H3N2 virus) – estimated deaths 1 million worldwide; 100,000 in the U.S.
  • 2009 influenza pandemic, also called swine flu (H1N1 virus, but a different strain from the 1918 flu pandemic) – estimated deaths 150,000-575,000 worldwide; 12,500 in the U.S. For this post I am using a figure of 400,000 deaths worldwide.
Comparison to the COVID-19 Pandemic

The current pandemic is caused by a coronavirus, which is a different group of viruses from influenza viruses. Like the flu, however, COVID-19 is spread primarily through the air.

As I write this, there have been approximately 200,000 deaths worldwide (source); approximately 50,000 deaths in the U.S. (source); and 44 deaths in Vermont (source). Comparable statistics for earlier dates: March 26 and April 4.

Here is a comparison of the worldwide deaths (click on any image to enlarge):

The pandemics of the last 65 years look insignificant compared to the Black Death and the 1918 flu pandemic. The disparity is even greater when considered as a percentage of world population, as shown in the following table:

[World population numbers from here (historical) and here (current). I did some rounding.]

Now let's look at just the pandemics of the last 65 years (i.e., excluding the Black Death and the 1918 flu pandemic) and include the U.S. numbers. The following graph shows total deaths, not as a percentage of population:

On a worldwide basis, total deaths to date from the current coronavirus pandemic are approximately half of the 2009 pandemic and do not yet approach the pandemics of 1957 and 1968. In the United States, however, COVID-19 deaths to date are four times the deaths from the 2009 flu and approximately half of the deaths from the 1957 and 1968 flus.

As we think about the future we should keep in mind that, like the influenza pandemic of 1918, there may be more than one wave of the current COVID-19 pandemic.

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