Does trying to live healthy make sense considering an imminent bird flu outbreak?

[Astreja]

There’s nothing to explain - you’re simply wrong. A vegan diet does not protect against COVID or make you more susceptible to bird flu.

Boru

But how could a diet that boosts your immune system not do that?

To a large extent, susceptibility to an infectious agent is dose-dependent.  If you have just a glancing encounter with the virus you'll generally do better than someone who's in a situation that exposes them to a high viral load.  The immune system still has to recognize the virus and produce antibodies, which is why vaccination is better than relying on diet.