Because for your body to fight a virus, it needs to have a good working immune system. Some people lack that for various reasons. A vaccine helps in this case but it's not 100%.
Being "fit" certainly helps your immune system. But as we see here, it doesn't make you invincible.
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Do we know why some vaccinated people still die of Covid? That would probably help a lot in figuring out who will benefit from the vaccine.
Because for your body to fight a virus, it needs to have a good working immune system. Some people lack that for various reasons. A vaccine helps in this case but it's not 100%.
Being "fit" certainly helps your immune system. But as we see here, it doesn't make you invincible.