Modern vaccines prevent diseases that were common, debilitating and even deadly a generation ago. Vaccination eradicated smallpox worldwide and almost eradicated polio from the UK. In that country the incidence of measles, mumps and rubella fell from between 160 000 and 800 000 per year before the introduction of vaccination, to 5000 per year today. However, the potential of vaccines is far from exhausted. Almost every week there is a report about advances in vaccines against diseases as diverse as meningitis, herpes and even nicotine and cocaine addiction. Many biotechnology products overcome the limitations of traditional vaccines which use either killed or disabled whole pathogens to produce the immune response.