Finding a new vaccine begins with understanding the structure of the virus or bacterium and how it causes the infection which are you are trying to prevent. Vaccines contain a harmless form of the bacteria or virus that causes the disease.
This means the bacteria or virus will be killed, greatly weakened, or broken down into small parts before being used to trigger an immune response in the person receiving the vaccine but without making them ill.
Carefully working out how to do this and selecting appropriate technologies happens in pre-clinical testing. It is then a case of thoroughly testing a vaccine through clinical trials to make sure it’s effective and safe to use.
Historically, developing a new vaccine has required: