1918 Influenza Pandemic Case Fatality Rate


Influenza viruses and birds. Russell Kightley Media

Seeing as I have written an ebook on influenza that includes a short history of the 1918 pandemic, I have a rather keen interest in looking up things like case fatality rates, incidences and the like. I have also picked up on a rather worrying discrepancy in oft-quoted figures that just get recirculated without question, in serious and respected publications.

For example, here is one of the opening paragraphs from an influential review from Jeffery Taubenberger and David Morens, from 2006:

“An estimated one third of the world’s population (or ≈500 million persons) were infected and had clinically apparent illnesses during the 1918–1919 influenza pandemic. The disease was exceptionally severe. Case-fatality rates were >2.5%, compared to <0.1% in other influenza pandemics. Total deaths were estimated at ≈50 million and were arguably as high as 100 million.”

This figure of ~2.5% CFR is found in many references, yet it cannot be right: just from data in that paragraph, one could estimate that the CFR must have been between 10 and 20%!

No less a publication than Nature, in their 25th January issue, has an editorial entitled “The Great Flu” – wherein they say the following – and add to the problem:

“One hundred years ago this month, the 1918 influenza virus was just starting to spread. It would become the greatest public-health crisis of the twentieth century, claiming some 50 million to 100 million lives….

There are few data points to go on — flu pandemics happen only three or four times a century — but one risk is certainly higher: 7.6 billion people share the planet in 2018, up from 1.9 billion in 1918….

The case-fatality rate in the 1918 pandemic was around 2.5% (compared with less than 0.1% in other flu pandemics), and a comparable or worse rate in a future pandemic cannot be discounted.”

pig flu

Influenza viruses in pigs. Russell Kightley Media

From their own figures, then, between 50 and 100 million people died, of 1.9 billion alive at the time. This is a death toll of between 2.6 and 5.2% of the WHOLE POPULATION, and is NOT a case fatality rate. If about one-third of the population was affected, then the CFR would be ~7.5 – 15%, which is far higher than the 2.5% quoted.

Here is a more realistic quote, for me at least, from Influenza Virus Net.com:

“The global mortality rate from the 1918/1919 pandemic is not known, but it is estimated that 10% to 20% of those who were infected died. With about a third of the world population infected, this case-fatality ratio means that 3% to 6% of the entire global population died. Influenza may have killed as many as 25 million in its first 25 weeks. Older estimates say it killed 40–50 million people while current estimates say 50—100 million people worldwide were killed. This pandemic has been described as “the greatest medical holocaust in history” and may have killed more people than the Black Death.”

Wikipedia even seems to have got it right, in their entry on the 1918 pandemic:

“The global mortality rate from the 1918/1919 pandemic is not known, but an estimated 10% to 20% of those who were infected died. With about a third of the world population infected, this case-fatality ratio means 3% to 6% of the entire global population died.

 So, all you virologists out there: please stop quoting that ludicrously low case fatality rate for the 1918 influenza pandemic of 2.5%, and get real! Oh, and let’s stop calling it the “Spanish Flu” too, please: it’s a much a misnomer as “swine flu” is for the 2009 pandemic, or “Aussie Flu” is for the recent and ongoing H3N2 epidemic.

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