How Do Vaccines Work?

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Vaccines and the Immune System

Key Terms:

  • Antigen: a foreign substance which induces an immune response in the body
  • Antibodies: proteins produced by the body in response to an antigen; antibodies combine chemically with antigens
  • Phagocytes: cells of the immune system responsible for digesting and degrading pathogens


 Vaccines work directly with the immune system to safely protect the body from the disease.
  • Vaccines contain a killed or weakened form of a virus or bacteria, known as antigenic components, that are introduced to the body, either intranasally, orally, intradermally, or intramuscularly.
    • Intranasally: administered by way of the nose (spray)
    • Orally: administered by way of the mouth (pill, liquid)
    • Intradermally: administered through the top layer of the skin
    • Intramuscularly: administered through the muscle layer of the skin
  • These antigens do not cause illness on their own. Instead, these antigens cause the immune system to mount a response. The response includes sending white blood cells to the site to destroy the invader.
    • Some of these cells create antibodies that surround the antigen, acting like a signal for the other white blood cells to attack.
    • Antibody:Antigen binding may result in:
      • Agglutination: clumping together of antigens, which makes them more easily digested by phagocytes
      • Neutralization: prevents the virus from attaching to receptors on our own cells
      • Opsonization: coating of pathogens to enhance digestion by phagocytes
      • Complement activation: causes inflammatory response to bring more immune cells to the infection site
      • Antibody-dependent cytotoxicity: degradation of the infected cell
    • Antibodies are produced against antigens in a lock-and-key fashion. You have billions of antibodies in your body against pathogens that you have seen since you were born!

Image Source: Boundless

  • Memory cells of the immune system will remember the antigen, and will remain in the body for a long time.
    • If the body encounters the same antigen again, the memory cells allow the immune system to mount a fast and effective immune response to destroy the antigen before it has the chance to cause illness.
Image Source: The Open Door Website

By previously being exposed to the harmless antigen in vaccines, you protect yourself from contracting the disease!

Image result for vaccine and immune system cartoon

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