Vaccines

Source: MedlinePlus Health Topics, U.S. National Library of Medicine

Last synced 8/7/2026Status: primary verified

What are vaccines? Vaccines are injections (shots), liquids, pills, or nasal sprays that you take to teach your body's immune system to recognize and defend against harmful germs. For example, there are vaccines to protect against diseases caused by: Viruses , like the ones that cause the flu and COVID-19 Bacteria , including tetanus, diphtheria, and pertussis What are the types of vaccines? There are several types of vaccines: Live-attenuated vaccines use a weakened form of the germ. Inactivated vaccines use a killed version of the germ. Subunit, recombinant, polysaccharide, and conjugate vaccines use only specific pieces of the germ, such as its protein, sugar, or casing. Toxoid vaccines use a toxin (harmful product) made by the germ. mRNA vaccines use messenger RNA, which gives your cells instructions for how to make a protein (or piece of a protein) of the germ. Viral vector vaccines use genetic material, which gives your cells instructions for making a protein of the germ. These vaccines also contain a different, harmless virus that helps get the genetic material into your cells. These vaccines may work in different ways, but they all spark an immune response. The immune response is the way your body defends itself against substances it sees as foreign or harmful. These substances include germs that can cause disease. What happens in an immune response? There are different steps in the immune response: When a germ invades, your body sees it as foreign. Your immune system helps your body fight off the germ. Your immune system also remembers the germ. It will attack the germ if it ever invades again. This "memory" protects you against the disease that the germ causes. This type of protection is called immunity. What are immunization and vaccination? Immunization is the process of becoming protected against a disease. But it can also mean the same thing as vaccination, which is getting a vaccine to become protected against a disease. Why are vaccines important? Va

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This information is for general education and is not medical advice. Always talk to a licensed U.S. clinician about your situation, medications, or treatment decisions.