Vaccines are one of the biggest success stories of modern medicine. The CDC estimates that vaccination of children born between 1994 and 2021 in the U.S. will prevent 472 million illnesses and help avoid 1,052,000 deaths.
Currently, the US has the safest vaccine supply in the world, but loud voices on social media would have you believe otherwise. The fact is vaccines are safe, and they are effective. So effective that many diseases have become rare, and some have even been eradicated. This success stems from decades of research, trials, and innovation.
All vaccines in the U.S. go through a series of phases before they are recommended and become available for use:Â
- Development
- Approval
- Production
- Added to the U.S.-recommended immunization schedule
- Safety monitoring
Development
Researchers spend years testing the vaccine before moving to clinical trials during the development phase. Clinical trials consist of three phases.
- During phase 1, 20 – 100 volunteers are given the vaccine. Researchers monitor the volunteers to determine if the vaccine is working, is safe, if the proper dose was administered, and if there are any side effects.
- In phase 2, hundreds of volunteers are given the vaccine, and researchers look for any short-term side effects and determine how the volunteers’ immune systems respond.Â
- A hundred to potentially thousands of volunteers are given the vaccine, an alternative vaccine, or a placebo in the final phase. Then their immune responses and any side effects are compared with each other.
Approval
Before a vaccine can be approved, data collected during the development phase is reviewed by the Food and Drug Administration (FDA) and the Vaccines and Related Biological Products Advisory Committee (VRBPAC) to determine if it is safe and effective. Once the vaccine is approved, it is cleared for production.
Production
When vaccines are manufactured, the FDA monitors the process and regularly inspects manufacturing facilities to ensure they adhere to strict regulations. Vaccines are produced in batches called lots; each lot of a vaccine must be tested to ensure they are safe, pure, and potent.
Addition to Schedule
Before a vaccine can be added to the recommended immunization schedule, the Advisory Committee on Immunization Practices (ACIP) must approve it. The medical and public health experts that make up the ACIP review the data and decide whether to recommend it to the Centers for Disease Control and Prevention (CDC). If the CDC accepts the recommendation, the vaccine becomes part of the schedule.
Ongoing Safety Monitoring
Once a vaccine is on the schedule, it continues to be monitored by the FDA and the CDC for any potential side effects. They do this by reviewing the Vaccine Adverse Event Reporting System (VAERS), Vaccine Safety Datalink (VSD), the Post-Licensure Rapid Immunization Safety Monitoring (PRISM) system, and the Clinical Immunization Safety Assessment Project (CISA).
Vaccine Safety Resources
- The IIC vaccine safety sheet
- Children’s Hospital of Philadelphia vaccine safety page
- The CDC’s vaccine information for parents and caregivers
