"Before a vaccine is licensed and brought to the market, it undergoes a long
and rigorous process of research, followed by many years of clinical testing.
The overall development of a vaccine consists generally of a discovery phase,
a pre-clinical phase, the clinical development phase (phases I to III) and the
post licensure phase (phase IV), and it takes on an average about 10 to 15 years."
https://www.ifpma.org/wp-content/uploads/2019/07/IFPMA-ComplexJourney-2019_FINAL.pdf