"Adaptive immunity responds to the challenge with a high degree of specificity as well as the remarkable property of
“memory.” Typically, there is an adaptive immune response
against an antigen within five or six days after the initial exposure to that antigen. Exposure to the same antigen some
time in the future results in a memory response: the immune
response to the second challenge occurs more quickly than
the first, is stronger, and is often more effective in neutralizing and clearing the pathogen."