How are vaccines developed and approved?
Check out the interactive chart below to learn more about how vaccines are developed.
Early Development
During this first stage of vaccine development, researchers work to identify substances that may be useful as vaccines. This early research is often performed by researchers at medical centers.
Pre-Clinical Studies
During this stage, scientists test the safety and efficacy of potential vaccines in tissue samples and lab animals. These studies help tell scientists how vaccines work in living tissue, what the appropriate dosage of the vaccine should be, and how it should be administered.
Human Studies
The vaccine must then be tested in 3 types of trials with human participants:
Phase I Trials: Smaller-scale trials (usually <100 people) that help determine if a vaccine is safe to use in humans, and whether or not it works the way it is supposed to.
Phase II Trials: Slightly larger trials (several hundred people) that help determine the appropriate dose for the vaccine, as well as the vaccine’s safety and efficacy.
Phase III Trials: Large-scale trials (usually thousands of people) that assess a vaccine’s safety and efficacy.
Approval and Licensing
After finishing a Phase III trial, the company submits the data to the FDA. The FDA thoroughly reviews the company’s data and inspects the facilities where the vaccine will be made. Once the FDA approves the vaccine, it can be made available to the public.
Ongoing Monitoring
Vaccine monitoring doesn’t just stop at approval. Even after it’s made available to the public, the FDA and the manufacturer both continue to carefully monitor the vaccine’s safety, efficacy, and production.

Before any vaccine is approved, it must be studied for many years and tested in clinical trials involving several hundred to several thousand volunteers.

Questions about vaccination
Common questions about vaccination
FDA = Food and Drug Administration.

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