A vaccine needs years of research to get permission for being used in clinics. these are the stages that a vaccine goes through to receive approval.
PRECLINICAL TESTING: Scientists test a new vaccine on cells and then give it to animals such as mice or monkeys to see if it produces an immune response.
PHASE 1 SAFETY TRIALS: Scientists give the vaccine to a small number of people to test safety and dosage, as well as to confirm that it stimulates the immune system.
PHASE 2 EXPANDED TRIALS: Scientists give the vaccine to hundreds of people split into groups, such as children and the elderly, to see if the vaccine acts differently in them. These trials further test the vaccine’s safety.
PHASE 3 EFFICACY TRIALS: Scientists give the vaccine to thousands of people and wait to see how many become infected, compared with volunteers who received a placebo. Rare side effects will be revealed during this phase.
EARLY OR LIMITED APPROVAL: Some countries like China, Russia have given emergency authorization based on preliminary evidence that they are safe and effective.
APPROVAL: Regulators review the complete trial results and plans for a vaccine’s manufacturing, and decide whether to give it full approval.
COMBINED PHASES: One way to accelerate vaccine development is to combine phases. Some vaccines are now in Phase 1/2 trials, for example, which this tracker would count as both Phase 1 and Phase 2.
PAUSED or ABANDONED: If investigators observe worrying symptoms in volunteers, they can pause the trial. After an investigation, the trial may resume or be abandoned
(ref: The New York Times: coronavirus vaccine tracker)