Vaccination is the most important thing we can do to protect ourselves and our children against ill health. They prevent millions of deaths worldwide every year.Since vaccines were introduced in the UK, diseases like smallpox, polio and tetanus that used to kill or disable millions of people are either gone or are now very rarely seen.Other diseases like measles and diphtheria have reduced to a very low number of cases each year since vaccines were introduced. These cases are often related to travel.However, if people stop having vaccines, it's possible for infectious diseases to quickly spread again.