[klipt]

The first wave of the Spanish Flu mostly killed the elderly. The second wave mutated and killed young, normally healthy people: https://en.wikipedia.org/wiki/Spanish_flu#Deadly_second_wave

[CraigJPerry]

I see that same line being peddled out of context like this frequently these days. When you point out the young people factor you really also need to point out why that was the case and it wasn’t because of the mutation of the virus...

[klipt]

Wikipedia says it was a mutation, although the selective pressure on that mutation (war) is something we hopefully won't have in today's circumstances.