eli5: Why was the second wave of the Spanish Flu so much deadlier than the first?
In: Biology
That is not widely accepted a true. A second wave in the US is believed to have killed more people because of wartime movements and other circumstances such as coinciding with season flu and pneumonia, some speculate the virus causing the Spanish Flu mutated and this is partly to blame – In short, no one knows exactly why.
As others have said, could be bad reporting. War-time censorship meant it wasn’t spoken about much in the media, which is why it’s known as the “Spanish Flu” because they didn’t have such restrictions on reporting, plus the King had it so it was a major news story.
The other reason was possibly a “reverse” of the usual mutation and spreading patterns of a strain of flu. Normally, those who are mildly ill would be out and about spreading it, those more ill would stay at home, not spreading it. The virus then “evolves” into a less deadly strain.
But because this was in WW1, the reverse happened – soliders with a mild strain stayed put in heavily fortified areas (trenches, etc), not mixing with civilians. While the seriously ill were sent to field hospitals, etc to be treated by civilian volunteers. So the deadlier strain spread more quickly.
We do not know. One theory is that it was due to a mutation of the flu making it more deadly. It is also possible that the reporting on the number of dead was wrong. First wave hit when soldiers were moving to the front and nobody knew about the flu, second wave hit when soldiers were going home and everyone were looking out for the flu. A soldier dying in the trenches from an unknown illness is likely not going to be counted the same as a soldier dying from an illness on the way home in the middle of a known widespread pandemic.
The 1918 flu pandemic not only happened in the middle of a world war but also in the early development of our understanding of infectious diseases. We did not have to tools and techniques to study and track the flu like we do today so there is a lot of things we do not know about it. And the techniques used to combat the current pandemic is techniques that were developed during the 1918 flu pandemic. Restrictions such as limiting the number of people together, canceling public events, closing boarders or at least quarantine people who travel, regularly washing of hands and face, stopping the exchange of spit, etc. were all implemented during the 1918 flu pandemic and were shown to be highly effective. And then just as now the cities that did not take effective measures early had field hospitals overflowing with sick, morgues running out of space and people buried in mass graves.
For new diseases in general the good thing about a first wave is it starts with one person in one place.
The problem is it takes time to get noticed and time to understand how to make good decisions. Also nobody has resistance yet.
The second wave is the opposite. A second wave can start from thousands of places at once. You know how to fight it. But if you aren’t making good decisions you have mostly negatives.
[This video series explains the history of Spanish flu ](https://www.youtube.com/playlist?list=PLhyKYa0YJ_5BZ3gQleTk-PJqIejFf4Rh2) in a very ELI5 way, while being very complete and thorough.
Basically, we don’t know that it was deadlier for sure, though most evidence seems to point to that being true. There are quite a few hypotheses as to why that might be including viral mutations, troop movements, immunity from the first wave, etc.
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