It could also be that cytokine storms were not known in 1979. The source I see o...

It could also be that cytokine storms were not known in 1979. The source I see on wikipedia is for 1991, but you can read the article if you like. [1]

This is what essentially causes the "W" curve as opposed to Covid-19's "J" curve.

Edit: Also as opposed to normal flu's "V" curve.

[1] https://en.wikipedia.org/wiki/Cytokine_release_syndrome