Vaccination

Vaccination is one of the most important medical developments in history. It has saved hundreds of millions of lives and led to the eradication of smallpox. In this lesson you will learn how vaccines work, what herd immunity is, and the benefits and limitations of vaccination programmes.

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What Is a Vaccine?

A vaccine is a preparation containing a dead or weakened (attenuated) pathogen, or parts of the pathogen (such as surface proteins or inactivated toxins).

When injected into the body, the vaccine stimulates the immune system to mount a response without causing the disease.

Key Point

The pathogen in the vaccine is either:

• Dead (killed) — cannot reproduce or cause disease
• Weakened (attenuated) — alive but significantly less dangerous; can reproduce slowly but cannot cause serious disease
• A fragment of the pathogen — e.g. surface antigens or inactivated toxins (toxoids)

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How Vaccination Works

The mechanism relies on the immune system's ability to form memory cells:

Step-by-Step Process