Vaccinations contain weakened or inactivated forms of a virus or bacteria, or parts of the virus or bacteria (such as proteins or sugars) that are specific to that virus or bacteria. When these are injected into the body, they stimulate the immune system to produce antibodies against the specific antigen present in the vaccine. This antigen activates the immune response, causing the body to create memory cells that can quickly recognize and fight off the actual virus or bacteria if it is encountered in the future.
