Secondary response, or the second wave of response, happens when the immune system encounters a pathogen for the second time. This time, the immune system responds faster and more efficiently due to the memory cells that were formed during the first encounter. Synonyms for secondary response include anamnestic response, memory response,s and recall response. These phrases depict the fact that the immune system has a recollection of the pathogen, allowing them to fight it off more effectively. The secondary response is crucial in vaccine effectiveness, as it is expected to provide lasting immunity against further exposures to the same pathogen.