As Bani is a naagin & strongest amoung her clan , when veer was poisoned by nagfani poison , she saved veer from her poison.
In S1 shivanya told in childhood when shesha bit her , then her mother gave some poison of shesha , that's why shesha can't kill her with biting as shivanya will not be effected by it.
Acc to this logic veer has no become totally safe from poison coz bani's poison was very strong & janeleva types. Any kind of poison wi not effect him as he has a bit of bani's poison inside him .