Ensuring Vaccine Safety

The United States has the safest, most effective vaccine supply in its history. The nation’s longstanding vaccine safety system ensures that vaccines are as safe as possible. As new information and science become available, the system is updated and improved.

As part of these vaccine safety efforts, scientists ensure the safety of vaccines by conducting different types of studies:

• Clinical trialsexternal icon are done before a vaccine is made available. Vaccine manufacturers conduct these studies as part of the development, testing, and approval process. The Food and Drug Administration (FDA) uses the information from clinical trials to decide if a vaccine is safe, effective, and ready to be licensed for use.
• Post-licensure safety studies are conducted after a vaccine is approved and in use. These studies are part of continuous vaccine safety monitoring and often look at populations that might be underrepresented in clinical trials. Importantly, these studies can look for rare adverse events.