Final answer:
An immune response to an antigen may result not only in protective immunity but also a detectable reaction to challenge with that antigen called a secondary adaptive immune response.
Step-by-step explanation:
An immune response to an antigen may result not only in protective immunity but also a detectable reaction to challenge with that antigen called a secondary adaptive immune response. This secondary response is stronger and faster than the initial response, and it is the basis of immunological memory, which protects us from getting diseases repeatedly from the same pathogen.