Immunisation is a way of protecting against serious diseases. Once we have been immunised, our bodies are better able to fight these diseases if we come into contact with them.
Before vaccines were available, many children in the UK died from diseases such as whooping cough, measles and polio.
When enough people are immunised diseases cannot spread.
Immunisation is one of the biggest health successes of the last century.
Years of extensive laboratory and clinical tests are undertaken during a vaccine's development.