Vaccine
Talk

How do vaccines work?

To understand how vaccines work, it helps to first look at how the body fights illness. When germs, such as bacteria or viruses, invade the body, they attack and multiply. This invasion, called an infection, is what causes disease. The body has many ways of defending itself against pathogens. A pathogen is a bacterium, virus, parasite or fungus that can cause disease within the body. Each pathogen is made up of several subparts, usually unique to that specific pathogen and the disease it causes Skin, mucus, and cilia (microscopic hairs that move debris away from the lungs) all work as physical barriers to prevent pathogens from entering the body in the first place.

The immune system uses your white blood cells to fight infection.These white blood cells consist primarily of macrophages, B-lymphocytes, and T-lymphocytes: Macrophages are white blood cells that swallow up and digest germs, plus dead or dying cells. The macrophages leave behind parts of the invading germs called antigens. The body identifies antigens as dangerous and stimulates antibodies to attack them. B-lymphocytes are defensive white blood cells; they can produce antibodies to fight off infection. T-lymphocytes are another type of defensive white blood cell, that recognizes a familiar germ, if the body is exposed again to the same disease.

The first time the body is infected with a certain pathogen, it can take several days for the immune system to make and use all the tools needed to fight the infection. After the infection, the immune system remembers what it learned about how to protect the body against that disease. If your body encounters the same germ again, the T-lymphocytes recognize the familiar pathogen, and the B-lymphocytes can produce antibodies to fight off infection.

Vaccines can help protect against certain diseases by imitating an infection. This type of imitation infection helps teach the immune system how to fight off a future infection. 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. Then the vaccinated body is left with a supply of T-lymphocytes and B-lymphocytes that will remember how to fight that disease.

However, it typically takes a few weeks for the body to produce T-lymphocytes and B-lymphocytes after vaccination. Therefore, it is possible that a person infected with a disease just before or just after vaccination could develop symptoms and get that disease, because the vaccine has not had enough time to provide protection. While vaccines are the safest way to protect a person from a disease, no vaccine is perfect. It is possible to get a disease even when vaccinated, but the person is less likely to become seriously ill.