Symptoms and Infectivity - the Order Matters

In the age of COVID-19, we hear a lot about the Spanish flu epidemic from 1918-19. Though it was found in the US, France, Germany and UK first, yet it came to be called the Spanish flu. Why? Because it happened during a World War!

“To maintain morale, World War I censors minimized these early reports. Newspapers were free to report the epidemic's effects in neutral Spain… these stories created a false impression of Spain as especially hard hit. This gave rise to the name "Spanish" flu.”

 

And how far did it spread and how many did it kill? Wikipedia again:

“It infected 500 million people – about a third of the world's population at the time – in four successive waves. The death toll is typically estimated to have been somewhere between 17 million and 50 million, and possibly as high as 100 million, making it one of the deadliest pandemics in human history.”

 

If that’s not scary, consider this additional point from David Quammen’s book on inter-species diseases, Spillover:

“That infamous global pandemic, remember, occurred in the era before globalization.”

And before aeroplanes made inter-country travel so fast and easy. How could that have happened?

 

Quammen doesn’t get into the transport/movement aspect of the issue. Instead, he asks (and answers) why the more recent SARS outbreak of 2003 didn’t spread as far and wide, in the era of aeroplanes and globalization? The advances in medical technologies aside, the bottom-line is that it was due to something in the nature of the diseases in the two cases.

“One further factor, probably the most crucial, was inherent to the way SARS-CoV (the SARS virus) affects the human body: Symptoms tend to appear in a person before, rather than after, that person becomes highly infectious… That order of events allowed many SARS cases to be recognized, hospitalized, and placed in isolation before they hit their peak infectivity.”

The Spanish flu, on the other hand?

“With influenza and many other diseases, the order is reversed, high infectivity preceding the symptoms by a matter of days.”

In other words:

“The (Spanish flu) bug travelled ahead of the sense of alarm.”

 

Which is why Quamenn says that the order of events (symptoms and infectivity) can be far more critical than anything else:

“This was an enormously consequential factor in the SARS episode – not just lucky but salvational.”