BEST Program

Biologics Effectiveness and Safety — FDA's active post-market surveillance of vaccines and biological products

What Is the BEST Program?

The Biologics Effectiveness and Safety (BEST) Initiative is an FDA program established in 2012 to monitor the safety and effectiveness of vaccines and other biological products after they are approved and in use. BEST uses large linked electronic healthcare databases to conduct rapid safety assessments of vaccines in near real-time.

BEST is the FDA's primary tool for post-market active surveillance of vaccines — complementing the CDC-managed VAERS (passive) and VSD (active) systems.

How BEST Works

Electronic Health Record Linkage

BEST accesses linked claims and electronic health record databases covering tens of millions of Americans, allowing rapid identification of potential safety signals.

Near Real-Time Monitoring

Unlike traditional surveillance that analyses data annually or quarterly, BEST can assess safety signals within weeks of a new vaccine deployment — critical during pandemic responses.

Effectiveness Monitoring

Uniquely, BEST monitors not just safety but also vaccine effectiveness in real-world populations — tracking how well vaccines perform outside controlled clinical trial settings.

Regulatory Action

When BEST identifies a confirmed safety signal, findings are reviewed by FDA scientists and can trigger label updates, prescribing guidance changes, or in rare cases, product withdrawal.

BEST vs. Other Safety Systems

Key differences between the three major U.S. post-market systems:

VAERS

CDC / FDA

Passive surveillance. Anyone can report. Cannot calculate rates. Best for signal detection. Managed by CDC and FDA jointly.

VSD

CDC

Active surveillance. 12 million covered lives. Can calculate rates and assess causation. Managed by CDC with nine HMO partners.

BEST

FDA

Active surveillance. Tens of millions covered. Near real-time. Monitors both safety AND effectiveness. FDA-managed.

Key BEST Findings

Selected findings from BEST published research:

COVID-19 Vaccines

BEST contributed to the characterisation of myocarditis/pericarditis risk following mRNA vaccination, particularly in young males after the second dose.

Influenza Vaccines

BEST studies have confirmed the effectiveness and safety profile of seasonal influenza vaccines across multiple seasons.

Guillain-Barré Syndrome

BEST investigations have examined GBS risk following influenza and other vaccines, contributing to updated clinical guidance.

Accessing BEST Research

Published Studies

BEST research is published in peer-reviewed journals including Vaccine, JAMA, and Pharmacoepidemiology & Drug Safety. Search PubMed for "BEST Initiative FDA" or "Biologics Effectiveness and Safety."

FDA BEST Overview

The FDA maintains a public summary of BEST methods and recent findings at fda.gov/vaccines-blood-biologics/biologics-effectiveness-and-safety-best-initiative

Sentinel System

BEST is part of the FDA's broader Sentinel Initiative for medical product safety. Full details at fda.gov/safety/fdas-sentinel-initiative

Sources & Citations

FDA. Biologics Effectiveness and Safety (BEST) Initiative. fda.gov, 2023.
Gee J et al. "Active surveillance for adverse events: the experience of the Vaccine Safety Datalink project." Pediatrics, 2003.
Anderson SA et al. "Vaccine safety monitoring in the United States: an overview." Drug Safety, 2015.
FDA Sentinel Initiative. fda.gov/safety/fdas-sentinel-initiative, 2023.