From preclinical research through FDA approval and post-market monitoring.
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.
Before human trials begin, vaccines undergo extensive laboratory and animal testing:
Human clinical trials proceed through three phases, each with increasing numbers of participants:
20-100 participants — Tests safety in small groups and identifies common side effects. Focuses on whether the vaccine produces an immune response.
100s of participants — Further evaluates safety and optimizes dosage. Includes diverse populations to assess immune response variations.
Thousands to tens of thousands of participants — Large-scale testing to confirm efficacy and monitor rare side effects. Compares vaccinated groups to placebo groups.
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:
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.
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.
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.
After approval, vaccines continue to be monitored for safety:
FDA approval is separate from vaccine recommendations. The Advisory Committee on Immunization Practices (ACIP) advises CDC on vaccine use. ACIP recommendations determine: