As much as 80% of population will have had that desease by the summer.

+++Tatiana! (только THE DISease)

Sveta, humans as opposed to what, aliens?

By the way, we also use % in English. Writing it out looks strange.

Not your best work :(

As much as 80% of population will have had the desease by the summer.

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by the summer, it(/the virus/the sickness) will have run it course in 80% of the population

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