# 5875
The largest die-off of humans in modern history took place between 1918 and 1919 during the great influenza pandemic. Estimates vary, but most scholars put the number of deaths between 40 million and 100 million worldwide.
More than 90 years later, there is still great disagreement and controversy over exactly what happened.
We know that there was a `herald wave’ in the spring of 1918, with apparently very low mortality. The flu arrived again in late summer, but this time was far deadlier. This 2nd wave lasted throughout the fall and was followed, in the spring of 1918, by a less severe 3rd wave.
Source CDC EID
Almost a century later, many questions abound.
Was the mild spring wave caused by the same virus as the deadlier wave that appeared in the fall?
If so, why was it so much deadlier in the 2nd wave?
Did catching the milder flu in the spring protect against catching the deadlier fall flu?
As Robert Roos of CIDRAP explains, recent attempts to resolve these questions have returned diverse and conflicting answers.
At this point I’ll just step out of the way, and invite you to read his terrific report:
Study suggests 1918 flu waves were caused by 'distinct' viruses
The 1951 flu season mentioned by John Barry in this article, where the seasonal flu inexplicably turned deadly across England and parts of eastern Canada for about 6 weeks, remains one of the great medical mysteries of the 20th century.
I’ve written about this event several times (see UK: Revisiting An Earlier Flu Epidemic and Sometimes . . . Out Of The Blue), but briefly:
During an otherwise unremarkable and mild influenza season, for about six weeks a highly virulent influenza erupted in Liverpool, England and then spread across the UK and to Canada – that for a time was as deadly as the 1918 pandemic.
This startling graphic comes from the March 16th, 1951 Proceedings of The Royal Society of Medicine – page 19 – and shows in detail the tremendous spike in influenza deaths in early 1951 over the (admittedly, unusually mild) 1948 flu season.
The CDC's EID Journal has a stellar account of this 1951 event, and is very much worth reading.
Viboud C, Tam T, Fleming D, Miller MA, Simonsen L. 1951 influenza epidemic, England and Wales, Canada, and the United States. Emerg Infect Dis [serial on the Internet]. 2006 Apr [date cited].
This aberrant strain never spread much beyond the UK and eastern Canada and died out as the flu season came to a close. Thankfully, and for reasons that remain a mystery, it did not return the following year.
What made it so virulent remains unknown, but it serves as a stark reminder that influenza can be unpredictable, and that even a mild season can turn deadly without warning.
For those who like their science neat and tidy, devoid of ambiguity, and rock solid . . . dueling studies such as the ones described above are no doubt more than a little disconcerting.
And we’ve seen similar (unresolved) debates over the efficacy of Tamiflu, the value of surgical masks in preventing respiratory infections, and the effectiveness of flu vaccines.
A few previous blogs on these uncertainties include:
RCTs: All That’s Gold Standard Doesn’t Glitter
None of this is intended to suggest that scientific research is useless, or fundamentally flawed.
Only that gaining scientific knowledge is a process . . . one that evolves over time and rarely proceeds in a linear fashion . . . and that scientific certainty is an elusive, sometimes unobtainable goal.
So the next time you see a study cited here (or any place else for that matter), keep in mind that while it may be useful . . . and it might even be correct . . .
You can’t count on it being the last word on the subject.
