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How Vaccines Work

Infections are unpredictable and can have long-term consequences. Even mild or symptom-less infections can be deadly. Vaccines help the body learn how to defend itself from disease without the dangers of a full-blown infection.78

The Body’s Defense Against Infection

To understand how vaccines work, it is helpful to first look at how the body fights illness. When germs, such as bacteria or viruses, invade the body, they attack and multiply. This invasion is called an infection, and the infection is what causes illness. The immune system uses several tools to fight infection.79

Click on the "components of the immune system" to learn more:

 

The first time the body encounters a germ, it can take several days to make and use all the germ-fighting tools needed, as described above, to get over the infection. After the infection, the immune system remembers what it learned about how to protect the body against that disease.80

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Vaccines Strengthen the Body’s Natural Defenses

A person who is immune can resist the bacteria or viruses that cause a disease. The CDC defines being immune as being partially or fully resistant to a specific infectious disease or disease-causing organism.81 Building that immunity can either be passive or activenatural or vaccine induced. Active immunity takes longer to develop but lasts longer than passive immunity, while passive immunity provides protection that is immediate but fades within weeks or months.81

 

Active immunity comes from being exposed to a disease-causing organism.81

    • Natural immunity results from being infected directly by a disease-causing organism, whether the infection is symptomatic or not.81
    • Vaccine-induced immunity results from being exposed to killed or weakened bacteria or viruses through vaccination.81

 

Passive immunity is provided by antibodies produced by another human being or animal.81

    • Full-term babies acquire passive immunity from their mother’s antibodies during the final months of pregnancy.81
    • Patients can acquire passive immunity through antibody-containing blood products derived from human or animal sources.81

To read more about the different types of immunity please reference the CDC- Immunity Types webpage.82