For a specific example the Spanish Flu hit harder later on.
Highly-deadly diseases will kill their hosts quickly, limiting their spread. Therefore, one of two things will happen:
• A less-deadly variant will emerge, spread faster, and outcompete its more deadly cousin.
• The deadly disease will kill enough of the population that its R number drops below 1, and thus the deadly disease will die out.
Therefore, observed diseases will tend to get less deadly over time.
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If you look at the data, we're firmly in “kill enough of the population” town (to the extent you can stretch this model to our situation). The variants we're seeing spread are getting more virulent over time, not less, because:
• we don't want to die and we're doing stuff about that, meaning any model with “most individuals infected are removed from the model” in it is a flawed model; and
• we have fast long-distance travel, so any population model that relies on Euclidean locality is a flawed model.
> Among five COVID-19 patients who were hospitalized, four were fully vaccinated
This isn't true. Given certain assumptions, it's true on average, but those assumptions don't apply in this case.