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Ensuring Vaccine Safety

	scientist working with microscope and specimenThe 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.

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How Vaccines are Tested, Licensed, and Monitored for Safety

Infographic showing the journey of a vaccine, from testing to use in the general public.

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Vaccine Safety Monitoring

Detailed information about the systems used to monitor vaccine safety.

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History of Vaccine Safety

Learn about the history of vaccine safety and monitoring in the United States.

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Understanding Side Effects and Adverse Events

Learn about the difference between a side effect and an adverse event.

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Vaccine Safety Partners

Visit the websites of CDC’s partners in vaccine safety.

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