Vaccine Safety

Vaccination is one of the best ways to prevent diseases. Over the past 50 years, essential vaccines saved at least 154 million lives (1). During the same period, vaccination has reduced infant deaths by 40%. Together with governments, vaccine manufacturers, scientists and medical experts, WHO's vaccine safety program is constantly helping monitor the safety of vaccines. This helps ensure that vaccines are safe for you and your family.

​In the United States, a number of safeguards are required by law to help ensure that the vaccines we receive are safe. Because vaccines are given to millions of healthy people—including children—to prevent serious diseases, they’re held to very high safety standards.

Every authorized or approved vaccine goes through safety testing, including:

• 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)

• Monitoring the vaccine’s safety after it is recommended for infants, children, or adults

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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.

During a clinical trial, a vaccine is tested on people who volunteer to get vaccinated. Clinical trials usually start with 20 to 100 volunteers, but eventually include thousands of volunteers. These tests can take several years and answer important questions like:

• Is the vaccine safe?

• What dose (amount) works best?

• How does the immune system react to it?

Throughout the process, FDA works closely with the company producing the vaccine to evaluate the vaccine’s safety and effectiveness. All safety concerns must be addressed before FDA licenses or authorizes a vaccine.

​Once a vaccine is approved or authorized, it continues to be tested. The company that makes the vaccine tests batches to make sure the vaccine is:

• 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)

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.

​Once a vaccine is recommended for use, FDA, CDC, and other federal agencies continue to monitor its safety.

​The United States has one of the most advanced systems in the world for tracking vaccine safety. Each of the systems below supplies a different type of data for researchers to analyze. Together, they help provide a full picture of vaccine safety.

• Vaccine Adverse Events Reporting System (VAERS): VAERS is an early warning system managed by CDC and FDA that is designed to find possible vaccine safety issues. Patients, health care professionals, vaccine companies, and others can use VAERS to report side effects that happen after a patient received a vaccine. Some side effects might be related to vaccination while others might be a coincidence (happen by chance). VAERS helps track unusual or unexpected patterns of reporting that could mean there’s a possible vaccine safety issue that needs further evaluation.

• The Vaccine Safety Datalink (VSD): VSD is a collaboration between CDC and several health care organiza