Immunity refers to the body's capacity to resist pathogen invasion. People are constantly exposed to pathogens, which are foreign disease-causing agents such as bacteria and viruses. Antigens are proteins that are bound to pathogens' surfaces and cause an immune response in the body.

A vaccine is a biological substance that provides active acquired immunity against a specific infectious disease. A vaccine usually contains an agent that looks like a disease-causing microorganism and is produced from weakened or destroyed microbes, their toxins, or one of their surface proteins.

An adjuvant is a component of certain vaccines that aids in the development of a stronger immune response in those who receive the vaccine. Adjuvants, in other words, aid the effectiveness of vaccines. Some vaccines containing naturally occurring adjuvants help the body develop a powerful defensive immune response and are made from weakened or killed germs.

A toxin that has been treated (usually with formaldehyde) to remove its toxic properties while maintaining its antigenicity, or ability to stimulate the development of antitoxin antibodies and thus produce active immunity. See the entries under vaccine for particular toxoids.

A vaccine is a portion of a germ that is safely introduced to your immune system so that it can learn how to combat that dangerous pathogen and protect your body in the future. Vaccines are vital because they can significantly minimise and prevent the spread of disease; in fact, some life-threatening diseases have been eradicated worldwide thanks to vaccines.