You Are Bitten by a Venomous Snake at a Nature

Essay

You are bitten by a venomous snake at a nature center. You are rushed to the emergency room and given an antiserum. The snake handler says that he was bitten previously, but did not need 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? If the snake handler has truly developed some level of immunity, then how has that happened?