[riri]

The Spanish flue had the same level of kill rate and contagion and it killed 40 million worldwide in its 8 month streak

What eventually makes something like this die out on it's own? It would seem it could just keep going on and on as long as it had peple to infect. Is there another factor that eventually "burns" these things out?

[JudgemAll]

It's a mystery why they burn out, but probably has to do with immunity. Those with the strong immunity survive the wave apparently. The Spanish flue attacked the young, this one is attacking the elderly.