Pneumonia, that quickly causes sepsis - perhaps from a compromised immune system, seems to be killing them.
Some people get a sepsis like syndrome from the flu itself. The flu also leaves you more vulnerable to pneumonia - as a secondary infection. The inflamed and denuded airways caused by the flu are very susceptible to bacterial superinfection particularly staph pneumonia. The folks I have in the hospital right now will be relieved to hear from those on this thread that think the flu epidemic is made up. They aren’t really sick and can just go home /s