The idea of a vaccine is simple: When the immune system is exposed to a weakened or dead version of a virus or bacteria, it produces antibodies to that disease. Antibodies are specialized proteins in the blood that go after and destroy viruses, bacteria, and other foreign substances.
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The next time that person is exposed to the same disease, their immune system remembers it and can quickly launch antibodies to fight off the infection. This is called immunity.
In the past, vaccines were used only to prevent disease. Today, researchers are creating vaccines that can actually treat conditions, including obesity. What sets the obesity vaccine apart from other weight-loss drugs is that it enlists the help of the immune system to induce weight loss.