Vaccines greatly reduce the risk of infection by working with the body’s natural defences to safely develop immunity to disease. They do this by imitating an infection. This type of infection, however, does not cause illness, but it does cause the immune system to generate T-lymphocytes, which in turn produce antibodies. Sometimes, after getting a vaccine, the imitation infection can cause minor symptoms, such as fever. Such minor symptoms are normal and should be expected as the body builds immunity.
Vaccines prime your immune system against future “attacks” by a particular disease. There are vaccines against both viral and bacterial pathogens (disease-causing agents).
When a pathogen enters your body, your immune system generates antibodies to try to fight it off. Depending on the strength of your immune response and how effectively the antibodies fight off the pathogen, you may or may not get sick.
If you do fall ill, however, some of the antibodies that are created will remain in your body, playing watchdog after you recover. If you’re exposed to the same pathogen in the future, the antibodies will ”recognize” it and fight it off.
Vaccines work because of this function of the immune system. They’re made from a killed, weakened, or partial version of a pathogen. When you get a vaccine, whatever version of the pathogen it contains isn’t strong or plentiful enough to make you sick, but it’s enough for your immune system to produce antibodies against it. As a result, if you’re exposed to the disease again, your immune system will recognize it and be able to fight it off.