Overview.
Before a vaccine is ever recommended for use, it’s tested in labs. This process can take several years. FDA uses the information from these tests to decide whether to test the vaccine with people.
Once a vaccine is approved, it continues to be tested. The company that makes the vaccine tests batches to make sure the vaccine:
Potent (It works like it’s supposed to)
Pure (Certain ingredients used during production have been removed)
Sterile (It doesn’t have any outside germs).

Every batch of vaccines is tested for quality and safety.
FDA reviews the results of these tests and inspects the factories where the vaccine is made. This helps make sure the vaccines meet standards for both quality and safety. Testing and evaluation of the vaccine before it’s licensed by the Food and Drug Administration (FDA) and recommended for use by the Centers for Disease Control and Prevention (CDC).