Before a new vaccine is ever given to people, extensive lab testing is done that can take several years. Once testing in people begins, it can take several more years before clinical studies are complete and the vaccine is licensed.
During the vaccine testing process, the Food and Drug Administration (FDA) sets rules for three phases of clinical trials to ensure the safety of volunteers. All vaccines are tested with adults first. The first phase tests 20-100 healthy volunteers, the second phase tests several hundred healthy volunteers, and the third and final phase tests hundreds to thousands of healthy volunteers. Once all phases have been completed, the FDA only licenses a vaccine if it’s safe and effective, and the benefits outweigh the risks.
Government agencies and their partners have established several 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 to help scientists monitor the safety of vaccines.
VAERS collects and analyzes reports of adverse events that happen after vaccination. Anyone can submit a report, including parents, patients, and healthcare professionals. The Vaccine Safety Datalink Project, a network of healthcare organizations across the U.S., analyzes healthcare information from over 24 million people, which scientists use to actively monitor safety. Vaccine recommendations may change if safety monitoring reveals new information on vaccine risks (like if scientists detect a new serious side effect).
The United States currently has the safest vaccine supply in its history. These vaccines keep children, families, and communities protected from serious diseases.