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I've seen arguments aired that #SARSCoV2 will 'weaken' because it 'pays a cost' by hurting its host. I'm afraid this is too simplistic and in fact incorrect. We cannot predict if the virus will become intrinsically more/less virulent based on evolutionary theory.
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The virulence/transmission tradeoff works under two conditions. The first is under 'vertical transmission' (i.e. mother to child), when fitness of the pathogen and the host are perfectly linked. A good example may be human cytomegalovirus (HCMV), which infects most of us.
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Attenuation also happens for extremely lethal pathogens. The textbook example is myxomatosis in rabbits. Upon it introduction in the 1950s in Australia, France and Chile, its case fatality rate was near 100%. Of note, it still kills 50-95% of the rabbits it infects today.
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The case case fatality rate of #SARSCoV2 is not high enough for natural selection to effectively reduce its virulence. Moreover, #COVID19 transmission is largely driven by asymptomatic/pre-symptomatic hosts. A strain that killed no patient would hardly transmit better.
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The morbidity/mortality burden of #COVID19 is expected to decrease significantly as the population acquires immunity through infection/vaccination. Though, there is no straightforward, sound evolutionary argument predicting #SARSCoV2 will become intrinsically less virulent.
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