You Are Bitten by a Venomous Snake at a Nature

You are bitten by a venomous snake at a nature center.A snake handler is also bitten.You are rushed to the emergency room and given an antiserum.The snake handler does not receive treatment because he said he was exposed to venom so many times that he is immune.What is antiserum and will you have long-lasting immunity to snake venom after this? Is what the snake handler said possible or should he also receive treatment? If he does not receive treatment and is not affected,what is protecting him?