Vaccines are made to protect us from serious diseases that can cause life-long illness, disability and even death. Vaccines work by inducing your immune system to create antibodies against a disease-causing pathogen. Vaccines contain very small amounts of virus or bacteria that have been altered or killed so they cannot cause the disease they are designed to protect you against. Most vaccines also contain adjuvants, which are substances that help the active ingredient of a vaccine get into the cells of your body more quickly and efficiently. They may also contain preservatives, such as thimerosal, to keep the vaccine from contaminated during production and storage, stabilizers, such as gelatin, and solvents.

The most important parts of a vaccine are the antigens, which stimulate your immune response. The most common antigens in vaccines are whole viruses or bacterium, or a weakened form of the toxins that a bacterium makes. Some vaccines use a gene from the pathogen to make mRNA that serves as the blueprint to create the protein the immune system needs. Other vaccines deliver the gene for a virus protein in a vector virus that doesn’t cause disease.

Once the vaccine is created, it is tested in labs in cell cultures and in animals (in a very humane way). After a vaccine is found to prevent disease and have few or no side effects, it can be tested on people in three phases. When the vaccine is proven safe and effective, it can be made widely available. Vaccines help protect you, your family and friends, and your community by providing “herd immunity” against disease. Without vaccination, disease outbreaks can occur, putting infants, older adults and people with weak immune systems at risk for life-threatening infections.