Currently, the United States has the safest, most effective vaccine supply in its history. Hundreds of medical studies completed over many decades by credible and respected doctors and scientists across the world have found that vaccines are safe for the overwhelming majority of children and adults. Clinical trials are conducted to evaluate the safety and effectiveness of a vaccine before it can be brought to market. Vaccines are first tested in laboratory studies and animal studies. Learn more about how vaccines are developed.

If the results indicate the vaccine is safe, additional testing in people must be done before the vaccine can be approved by the Food and Drug Administration. Learn more about how vaccines are licensed.

By the time a vaccine is offered to the public, it has been studied for at least 15 to 20 years in tens of thousands of study participants, by thousands of scientists, statisticians and health care providers.

Vaccine safety is a shared responsibility among the federal government, state and local health departments, health care providers and the public. To help meet this shared responsibility, government agencies and their partners have established several coordinated systems to monitor the safety of vaccines after they have been licensed for public use. These systems, such as the Vaccine Adverse Event Reporting System and the Vaccine Safety Datalink Project, are used together to help scientists monitor the safety of vaccines.

See the CDC infographic: The Journey of Your Child’s Vaccine

CDC: Vaccine Testing and the Approval Process
Children’s Hospital of Philadelphia: Process of Vaccine Development
Children’s Hospital of Philadelphia: Licensure, Recommendations and Requirements