<prompt> True about active immunityLess effectiveCan be given in immunodeficient stateImmunological memory presentNo lag period  <response>: When B cells and T cells are activated by a pathogen, memory B-cells and T- cells develop, and the primary immune response results. Throughout the lifetime of an animal these memory cells will remember each specific pathogen encountered, and are able to mount a strong secondary response, if the pathogen is detected again. Ref: Ananthanarayan Panikers textbook of microbiology 9th edition pg.no. : 81-84 