I suspect there are multiple causes to the reduction in #SARSCoV2 Case Fatality Rates (CFRs). Improved treatment undoubtedly plays a role. There might be some mortality displacement with a fraction of the population at particularly high risk having deceased early.
(1/4) https://twitter.com/skepticalzebra/status/1285520890810310658

Though, I suspect the lower CFRs and hospitalisation rates, as well as the possible increase in the proportion of asymptomatic cases may be largely due to how people get infected now, relative to the early stages of the pandemic.
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Infectious dose (i.e. the number of pathogens initiating an infection) is a well known factor for morbidity and mortality in animal experiments (including for #SARSCoV2). It is also suspected to play a role in influenza symptom severity.
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Outdoor transmission, social distancing and possibly facemasks are likely to have reduced the average infection dose in recent transmissions, and hence translated into lower CFRs and hospitalisation rates in many places. If this were true, CFRs might go up again in winter.
(4/4)