A vaccine is a biological preparation produced from a disease organism that enhances immunity against a disease by either preventing the disease (prophylactic vaccine) or in some cases treating the disease (therapeutic vaccine). A vaccine is prepared from weakened or killed form of microorganism. The four major types of vaccine are: live attenuated vaccine, inactivated vaccine, conjugate vaccine, and toxoid vaccine. Bacterial vaccines contain killed or attenuated bacteria that activate the immune system.

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