However, instead of one natural infection, for immunity to develop after a vaccine it usually takes several doses over several months or years. 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 s ever suffering through the disease.
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. Viruses are inactivated with chemicals such as formaldehyde. Toxoid vaccines are made by treating toxins with heat or chemicals, such as formalin, to destroy toxicity.