Influenza can kill older patients by paralyzing the immune system and causing secondary infections.

“the issue with influenza is that it can paralyze the immune system and it's these secondary infections that come in so so obviously there are certain strains of the flu that can kill you through the cytokine storm but isn't the way that the majority of older patients die of influenza is just that their immune system gets sort of whacked by this thing becomes almost somewhat paralyzed and they become more susceptible to other infections such as a bacterial infection isn't that a big part of the danger of influenza beyond just the virus itself”