Vaccine Approval Process
From preclinical research through FDA approval and post-market monitoring.
How Vaccines Are Approved
Vaccine development and approval in the United States follows a rigorous process designed to ensure safety and efficacy. This page provides an overview of each stage, from initial research through post-market surveillance.
The process involves multiple phases of clinical testing, extensive FDA review, and ongoing safety monitoring after approval.
Preclinical Research
Before human trials begin, vaccines undergo extensive laboratory and animal testing:
- Laboratory research: Identifying and synthesizing the vaccine antigen
- Animal studies: Testing safety and immune response in relevant animal models
- Manufacturing development: Scaling up production methods
Clinical Trial Phases
Human clinical trials proceed through three phases, each with increasing numbers of participants:
Phase I
20-100 participants — Tests safety in small groups and identifies common side effects. Focuses on whether the vaccine produces an immune response.
Phase II
100s of participants — Further evaluates safety and optimizes dosage. Includes diverse populations to assess immune response variations.
Phase III
Thousands to tens of thousands of participants — Large-scale testing to confirm efficacy and monitor rare side effects. Compares vaccinated groups to placebo groups.
FDA Review & Approval
Biologics License Application (BLA)
After successful clinical trials, manufacturers submit a Biologics License Application (BLA) to the FDA's Center for Biologics Evaluation and Research (CBER). The application includes:
- • All preclinical and clinical trial data
- • Manufacturing process details
- • Product labeling information
- • Risk management plans
FDA scientists review the entire application, often taking 6-12 months or longer for standard review. The Vaccines and Related Biological Products Advisory Committee (VRBPAC) provides independent advice.
Emergency Use Authorization vs. Full Approval
Emergency Use Authorization (EUA)
Used during public health emergencies when there is no adequate, approved alternative. Based on available evidence of "may be effective" and known potential benefits outweigh risks. Requires less comprehensive data than full approval.
Full Approval (Licensure)
Requires comprehensive data showing substantial evidence of safety and efficacy. Takes longer to complete full review. Once fully approved, the vaccine can be marketed and prescribed off-label.
Post-Market Surveillance (Phase IV)
After approval, vaccines continue to be monitored for safety:
- VAERS: Vaccine Adverse Event Reporting System — accepts reports from anyone
- Vaccine Safety Datalink: Active surveillance linking vaccination records to health outcomes
- Manufacturer requirements: Required to submit regular safety reports
ACIP Recommendations
FDA approval is separate from vaccine recommendations. The Advisory Committee on Immunization Practices (ACIP) advises CDC on vaccine use. ACIP recommendations determine:
- • Which vaccines are recommended for which age groups
- • Dosing schedules and intervals
- • Contraindications and precautions
- • Special populations (pregnant people, immunocompromised, etc.)