How Vaccines Work
Every day, the body is bombarded with bacteria, viruses and other germs. When a person is infected with a disease-causing germ, the immune system mounts a defense against it. In the process, the body produces substances known as antibodies against that specific germ. The antibodies eliminate the germ from the body. The next time the person encounters the germ, the circulating antibodies quickly recognize it and eliminate it before signs of disease develop.
This is why a child who has had chickenpox will only rarely develop the disease again. The immune system has memory. The next time the child encounters the virus that causes chickenpox, the antibodies destroy the virus before disease causes sickness. Medical experts estimate that the immune system can recognize and effectively combat hundreds of thousands, if not millions, of different organisms, or more.
A vaccine works in a similar way. However, instead of one natural infection, for immunity to develop after a vaccine it usually takes several doses over several months or years. The vaccine contains an inactivated (killed), weakened form of the germ, or a germ component. When introduced into the body, the dead or harmless germ causes an immune response without causing the disease. The immune system develops antibodies that will effectively kill or neutralize the germ if exposed to it in the future. The antibodies circulate in the bloodstream. Vaccination protects a child against infection with a germ without the child ever suffering through the disease.
Types of Vaccines
Vaccines can be developed in four different ways by using:
- Live bacteria or viruses that have been altered so that they cannot cause disease
- Killed bacteria or inactivated viruses
- Toxoids (bacterial toxins that have been made harmless)
- Parts of bacteria or viruses
Because the immune response may decrease over time, vaccines known as “boosters” are sometimes given to restore the immune response against that particular germ. Protective immunity lasts longer when boosters are given.
Live attenuated vaccines are usually derived from the naturally occurring germ. They can infect people, but not cause serious disease. Live attenuated vaccines are made by passing the virus through cell cultures over time until its disease-causing ability has deteriorated.