> > The epidemiological potential of a virus tends to unfold in waves. Age groups and geographical areas not affected 
> > initially are likely to prove vulnerable during the second wave. Subsequent waves have tended to be more severe, 
> > but for different reasons. In 1918, the virus mutated, within just a few months, into a far more virulent form. In 1957, 
> > schoolchildren were the primary vectors for spread into the general community during the first wave. 
> > The second wave reached the elderly, a group traditionally at risk of severe disease with fatal complications.
> ﾜｶﾘｶﾈﾏｽ

1918年の時は第2波はとんでもなく殺傷力の上がったウィルスに突然変異してしまっていて初回より死者がたくさん出たそうだ

参考：2020/05/20(水)19時25分44秒