How do vaccines work? Vaccines defend against deadly diseases. They do this by working with your body’s natural defenses to stop you from getting sick. When you get a vaccine, your immune system kicks into action. It recognizes the invading germ – like the virus or bacteria – and produces antibodies to fight it. If you come into contact with the germ later on, your body’s immune system quickly remembers how to destroy it, before you become unwell. The vaccine is a safe and clever way to produce