Vaccine
A vaccine is a shot that causes your immune system to make antibodies against a disease-causing pathogen. Some vaccines prevent disease, while others reduce the severity of illness if you do get sick. Vaccines take two to four years or more from the time government, academic or industry researchers start working on them until they are ready for human testing.
Vaccines contain weakened versions of viruses or bacteria (or a small amount of toxins made by bacteria) to create an immune response in your body without making you sick. Most vaccines use killed antigens, while some, including the shingles vaccine, use a live attenuated virus or a weakened form of a bacteria or toxin. Some vaccines contain adjuvants, which help the vaccine work well, and stabilizers that keep the vaccine from changing or spoiling during manufacturing and storage. Vaccines may also contain other ingredients, such as formaldehyde, which is used very early in the vaccine production process to kill or inactivate any bacteria or viruses, and neomycin, an antibiotic that can cause allergic reactions in some people.
Some vaccines use an animal model to test them, while others are tested with a large group of volunteers who receive a variety of doses and combinations of the vaccine. Vaccines go through several rounds of safety tests, and are only approved for use if they can protect the people who are in the trial without causing serious side effects. Some diseases, such as polio and measles, have been eliminated in the US because enough people got vaccinated, which is called herd immunity. Exciting new research is looking into cancer vaccines, which supercharge your immune system to destroy any cancer cells that hide from it.