4. How do vaccines work?

A pathogen is a bacterium, virus, parasite or fungus that can make you ill. One part of the pathogen is an antigen, which your body identifies as dangerous.

Your body produces antibodies which recognise the antigen and work with the rest of your immune system to destroy the pathogen and stop the disease. Each antibody in our system is trained to recognise one specific antigen.

When you meet an antigen for the first time, it takes a while for the immune system to respond and produce antibodies to fight that antigen. In the meantime, you can become unwell, sometimes seriously or even fatally.

Your body also creates antibody-producing memory cells. If you meet the same pathogen again, the antibody response is much faster and more effective than the first time.

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A vaccine is a tiny non-dangerous fragment which includes parts of the antigen from a specific pathogen (e.g. a bacterium, or virus like SARS-CoV-2 that causes COVID-19). It tells your body to build the matching antibody. If you encounter the real antigen later your body already knows how to defeat it. It can react quickly, and it is much less likely you will become ill with the disease.

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