A vaccine is a safe and effective way to protect people from disease. Vaccines work by triggering the body’s natural immune system without making people sick. Vaccines help prevent serious disease, disability, and death worldwide. In fact, a single vaccine can reduce a person’s risk of serious illness by as much as 90%.
Vaccines contain small amounts of dead or weakened (attenuated) bacteria, viruses, or other microorganisms. These are called antigens. The antigens either trigger the immune system to recognize and fight a specific pathogen, or they are used as a delivery vehicle for a pathogen’s toxins. Modern vaccines use many different methods for preparing pathogen antigens, including putting disease-causing virus or bacteria through several steps in cell cultures and animal embryos. Vaccines also include stabilizers, adjuvants, and preservatives like thimerosal.
The most common vaccines contain a killed, inactivated, or attenuated disease-causing virus. The virus is inactivated so it cannot reproduce or cause illness, but it still provokes the immune system to produce antibodies and memory cells. The resulting immunity can help protect people if they are exposed to the same pathogen in the future.
Some vaccines contain a live but very weakened virus or bacteria that is able to reproduce a few times, but not enough to cause disease. The weakened virus or bacteria stimulate the immune system to generate antibodies and memory B cells that can quickly respond to the threat and keep it from causing infection. These vaccines are typically given to young children and may require one or two doses.
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