That’s fairly typical of coronavirus patients; the virus gives them days to walk around, shedding infection upon everyone they come into close contact with. Given how contagious this disease is, and how severe the symptoms often become, if we tried a “quarantine the vulnerable” plan, it’s very likely that many hospitals would be overwhelmed even if they didn’t have any older patients.
Moreover, it’s not even possible to quarantine the vulnerable. Some 24 percent of adults between the ages of 55 and 64, and 21 percent of those over age 65, live in a multigenerational household. So, of course, do millions of younger immunocompromised or otherwise medically vulnerable adults and children.
If the rest of the populace is merrily going about its business, infecting each other with abandon, those people will inevitably get exposed unless the vulnerable ones can move to a separate household, or the other people in the household also self-quarantine indefinitely. Because people often live with relatives precisely because they can’t afford to live separately — much less off their savings — this is not very practical.