Acquired immunity is the resistance acquired by an individual during life and can be active or passive. Active immunity develops after natural infection or vaccination and stimulates both antibody-mediated and cell-mediated immunity, resulting in long-lasting protection. Passive immunity is induced by transferring preformed antibodies through maternal transfer to fetus/infant or injection of antiserum, providing immediate but short-term protection until the recipient can develop their own active immunity. Vaccines provide artificial active immunity and are prepared from live attenuated or killed microorganisms or their antigens.