How a new vaccine is developed, approved and manufactured For more information, visit FDA.gov/CBER FDA licenses the vaccine only if: It’s safe and effective Benefits outweigh risks Phase 1 20-100 healthy volunteers Vaccines are made in batches called lots. Several hundred volunteers Hundreds or thousands of volunteers Phase 2 Phase 3 The Food and Drug Administration (FDA) sets rules for the three phases of clinical trials to ensure the safety of the volunteers. Researchers test vaccines with adults first. What are the most common short-term side effects? How are the volunteers’ immune systems responding to the vaccine? How do people who get the vaccine and people who do not get the vaccine compare? Is the vaccine safe? Is the vaccine effective? What are the most common side effects? Is this vaccine safe? Does this vaccine seem to work? Are there any serious side effects? How is the size of the dose related to the side effects? Manufacturers must test all lots to make sure they are safe, pure and potent. The lots can only be released once FDA reviews their safety and quality. The FDA inspects manufacturing facilities regularly to ensure quality and safety.