Akio just got over having the flu. his brother just got the flu. his parents are not worried about akio getting it again because he built up an immunity to this flu strain. which explains the type of immunity he built up? active because he built up antibodies due to exposure to the flu active because his parents vaccinated him against the flu passive because his mother passed on the flu antibody passive because he had antibodies added to his blood

active because he built up antibodies due to exposure to the flu

Akio built active immunity because he built up antibodies due to exposure to the flu.Active immunity is a type of immunity which develops once a foreign antigen enters the body and after the exposure to such antigens, antibodies are made in the body.The antibodies created in response to the antigens are not only involved in neutralizing the antigen but besides this memory cells are also generated.Due to these memory cells, an active immunity is built which will allow protection from the same antigen on subsequent exposure.