>50 years is not old. I don't know what is considered old but I know that >75y has a two magnitudes higher mortality rate with the flu.

I doubt that the 50 years old Hospital doctor who died had any serious per-existing health condition. In fact, you could argue hat most doctors have a stronger immune system than average since they are exposed to more germs due to their profession. So this 50y old professional dropping dead is a bad sign! (and hands off to him for his bravery in doing his job).

You could only argue that he cough the strain very early. A virus jumping into a new species is more aggressive at the beginning, later it adopts more to the new host and becomes less aggressive.