Ensuring Vaccine Safety

The United States has the safest, most effective vaccine supply in its history.  The vaccine safety system ensures that vaccines are as safe as possible.

Scientists ensure the safety of vaccines by conducting different types of studies:

• Clinical trials are studies conducted before a vaccine is made available. These studies are carried out by vaccine manufacturers and help the Food and Drug Administration (FDA) make decisions about whether a vaccine is safe, effective, and ready to be licensed for use.
• Postlicensure studies are conducted after a vaccine is approved by FDA and made available to the public. These studies continue to monitor vaccine safety and often include groups that are often underrepresented in clinical trials. These studies can look for rare adverse events.