When the need for a vaccine has been established through research, scientists will work to identify vaccine components (the active ingredients which make the vaccine effective). Ongoing research will identify the impact of the vaccine and how it will be used.
Vaccines then go through a number of clinical trials where they are tested in different groups of people to determine safe dosage, effectiveness and side effects. Once these studies have been successful completed, the pharmaceutical company submit this data to the licensing agency. In Europe this is the European Medical Agency (EMA). The EMA consider whether the vaccine meets current EU legalisation requirements which include quality, safety and efficacy of the vaccine.
Once a vaccine has been granted a licence, it is up to each individual country to decide on its use. In the UK the Joint Committee for Vaccination and Immunisation (JCVI), consider all the evidence and recommend how and which vaccines are used in NHS programme. Once a vaccine is in the NHS programme ongoing surveillance monitors the impact of the vaccine, side-effects and how effective it is.