How do vaccines work?

Vaccines work by safely teaching your immune system to recognise a specific germ before you ever meet the real one. A vaccine contains a harmless piece or weakened form of a virus or bacterium, or instructions for your cells to make one such piece. Your immune system treats this as a threat and responds, producing antibodies and specialised memory cells. Because the vaccine cannot cause the actual disease, this training happens without you getting seriously ill. Later, if you encounter the real germ, your body recognises it and fights it off quickly, often before you notice any symptoms. When enough people are vaccinated, diseases struggle to spread, which protects the wider community too.