The next time I speak with my youngest son (who's company is presently working on a vaccine for COVID-19) I will ask him that question. That's an interesting point, but in reality the severity of any virus typically occurs only when it starts to mutate or change it's internal DNA structure. The virus itself, SARS-CoV-2 at this time has stayed remarkably consistent with no true mutations taking place. But, that could change and if and when it does one of two things will happen: it will become more virulent (and potentially sign it's own death warrant) or less virulent and possibly begin to produce symptoms more in line with the common cold. If the latter, it would potentially become more contagious but with milder symptoms. The number of reported infections would likely rise, but the death rate would begin to drop off significantly.