The quality or state of being epidemical; the characteristic of being widespread and rapid in affecting many people.
From 'epidemical' + '-ness' (forming abstract nouns indicating quality or state). This noun form allows discussion of the abstract quality of epidemic spread.
The 'epidemicalness' of a disease is how much it has that epidemic quality—high epidemicalness means it spreads fast and wide, like COVID-19 in 2020!
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