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State of Rhode Island Department of Health

Vaccine Safety

Vaccines are the best way to prevent serious illness and death from many infectious diseases. The Food and Drug Administration (FDA) adheres to rigorous testing standards before licensing vaccines. Licensed vaccines are then closely monitored through several national systems.

vaccine safety process

Vaccine Development

Vaccines are developed through the same general process used to develop drugs and medicines. A sponsor who wishes to begin clinical trials with a vaccine must apply to the FDA. In their application, they must describe the vaccine, how it’s manufactured, and quality control tests on the vaccine. Applications must also include information about the vaccine's safety and the results of testing in animals.

If the application is approved, the vaccine can be tested on people during clinical trials. These trials are typically done in 3 phases:

  • Phase 1 studies are performed in a small number of closely monitored subjects.
  • Phase 2 studies may enroll hundreds of subjects.
  • Phase 3 trials typically enroll thousands of people. These trials are used to document the effectiveness of the vaccine. They also provide important additional safety data required for licensing. 

If data at any stage of the animal or human studies raise significant concerns about either safety or effectiveness, the FDA may request additional information or studies or may halt ongoing clinical studies.

After reviewing clinical trial results and the proposed vaccine label, inspecting the facility where the vaccine will be made, and reviewing the vaccine production process, the FDA may decide to license the vaccine.

vaccine monitoring cycle

Vaccine Monitoring

Once licensed, vaccines continue to be closely monitored through several national systems, including the FDA’s Biologics Effectiveness and Safety (BEST) System and the Centers for Disease Control and Prevention’s (CDC) Vaccine Safety Monitoring Program. The CDC program includes the Vaccine Adverse Event Reporting System (VAERS) and Vaccine Safety Datalink (VSD) Project. Anyone can report a health problem to VAERS. Any problem with a vaccine may prompt further investigation by the CDC and FDA.

Trusted Resources

People with questions or concerns about vaccine safety should contact their healthcare professionals. Information found online should not replace the information given by a healthcare professional. However, there are several trusted organizations that parents and patients can turn to for additional information.