"Besides replicating very quickly, the 1918 strain seems to trigger a particularly intense response from the immune system, including a ‘cytokine storm’ – the rapid release of immune cells and inflammatory molecules.
Although a robust immune response should help us fight infection, an over-reaction of this kind can overload the body, leading to severe inflammation and a build-up of fluid in the lungs that could increase the chance of secondary infections.
The cytokine storm might help to explain why young, healthy adults – who normally find it easier to shake off flu – were the worst affected, since in this case their stronger immune systems created an even more severe cytokine storm."
BBC, Why the Flu of 1918 Was So Deadly
“Just as it was in the days of Noah, so will it be in the days of the Son of Man. People were eating, drinking, marrying and being given away in marriage, up to the very day Noah entered the ark. Then the flood came, and swept them all away.
And they said to him, 'Where will this happen, Lord?' And He said to them, 'Where death is, there a gathering of vultures will be.'”
Luke 17:26-27, 37