>it's a fair bit nastier, certainly in some cases, or the hospitals wouldn't be full
While I agree that it probably is indeed nastier than your average flu, it actually wouldn't have to be much nastier to achieve health system saturation in places where it hits groups that are particularly vulnerable (the elderly mainly). Almost all healthcare systems operate on fairly thin margins of tolerance for overload, and a virus of even mild percentages for hospital-worthy or lethal cases could easily, temporarily overload clinical infrastructure if it comes out of the blue and is moving through a population that was entirely virgin to it before the infection in question arrived. This lack of immunity among all parts of society means massive numerical surges in cases very quickly and consequently, major numerical surges in that small fraction of cases that end up being bad enough to warrant hospitalization.
While I agree that it probably is indeed nastier than your average flu, it actually wouldn't have to be much nastier to achieve health system saturation in places where it hits groups that are particularly vulnerable (the elderly mainly). Almost all healthcare systems operate on fairly thin margins of tolerance for overload, and a virus of even mild percentages for hospital-worthy or lethal cases could easily, temporarily overload clinical infrastructure if it comes out of the blue and is moving through a population that was entirely virgin to it before the infection in question arrived. This lack of immunity among all parts of society means massive numerical surges in cases very quickly and consequently, major numerical surges in that small fraction of cases that end up being bad enough to warrant hospitalization.