Active immunity is a type of immunity that occurs when the immune system is exposed to a pathogen, triggering the production of antibodies to that disease. Active immunity can be acquired through natural immunity or vaccine-induced immunity. Natural immunity is acquired from exposure to the disease organism through infection with the actual disease, while vaccine-induced immunity is acquired through the introduction of a killed or weakened form of the disease organism through vaccination. If an immune person comes into contact with that disease in the future, their immune system will recognize it and immediately produce the antibodies needed to fight it. Active immunity is long-lasting and sometimes life-long.