Who approves the use of vaccines in the United States?

The Food and Drug Administration (FDA) licenses and approves the use of vaccines. Before the FDA approves a vaccine, the manufacturer must do rigorous research and testing to ensure the vaccine’s safety and effectiveness. The FDA independently reviews and verifies the information from these tests. It then decides whether the vaccine can be licensed and given to the public.  In certain emergency situations, the FDA may issue an Emergency Use Authorization (EUA) to provide more timely access to critical medical products when there are no other options available.


How are vaccines tested for safety and effectiveness?

Vaccines must go through a detailed scientific evaluation before they can be submitted to the FDA for approval. Each phase of the evaluation includes three different clinical research studies. In the clinical research study or trial, people volunteer to be part of the study. Each clinical trial emphasizes safety of the vaccine on people. As the research moves through to the next phase, the group of volunteers becomes bigger to include more diversity in people and circumstances.

  • Phase 1 involves 20 to 100 healthy volunteers to evaluate safety and common side effects of the vaccine.
  • Phase 2 involves several hundred volunteers to gather information on safety, vaccine dosing, and ability to stimulate an immune response.
  • Phase 3 involves several thousand volunteers and a longer time frame than the earlier studies. Along with safety and side effects, most Phase 3 studies focus on efficacy -- how well the vaccine works in clinical trials -- and compare people who have received the vaccine to those who receive a placebo (a shot without the real vaccine).  During these studies, neither the participants nor the study managers know who received the vaccine and who received the placebo until the end of the study. This phase provides the most firm scientific evidence possible showing the difference between people who have been vaccinated and people who have not been vaccinated for both safety and effectiveness.


Who are the volunteers in vaccine clinical trials?

People volunteer to take part in clinical research studies. All study volunteers must go through a process called informed consent that ensures they understand all of the risks and benefits of being in a study, and those volunteers are reminded that they may leave a study at any time without losing any of their rights or benefits.

Each clinical trial emphasizes the safety of the vaccine on people. As the research moves through to the next phase, the group of volunteers becomes bigger to include more diversity in people and circumstances.  A diverse group of people volunteered to participate in every phase of the clinical trials, including populations disproportionately impacted by COVID-19 due to generations of systemic inequities.

For example, in Pfizer’s clinical trials, about 42% of volunteers identified as Asian, Black/African American, Hispanic/Latino/a, or Native American. About 37% of volunteers for Moderna’s trials identified as Asian, Black/African American, Hispanic/Latino/a, or other.



What happens after clinical trials are finished?

Once the clinical trials can demonstrate vaccine safety and effectiveness at an appropriate dose, the manufacturer applies to the FDA to license the vaccine so that it can be used in the general population.  The FDA reviews all of the data from the phased clinical studies using rigorous protocols and procedures.

The vaccine is not licensed or approved until the FDA can ensure the vaccine is safe and effective. In emergencies, such as the current COVID-19 pandemic, vaccines can also be authorized through an Emergency Use Authorization (EUA). The FDA usually authorizes an EUA for a specific population. After receiving an EUA, the manufacturer continues monitoring clinical trials as well as gathering and analyzing data. With more data, the manufacturer can then submit to the FDA for a Biologic License Application (BLA) so that the vaccine is able to be used more widely than originally covered in the EUA.


Who else reviews the safety and effectiveness data from the clinical trials?

For each vaccine authorized by the FDA, the Advisory Committee on Immunization Practices (ACIP) carefully reviews all available data about the vaccine from clinical trials and other studies, and makes recommendations for vaccine use in the general public. Recommendations include groups that should and should not receive the vaccine, as well as the timing, volume, number, and spacing of doses in a vaccine series. 

The ACIP is an independent advisory committee that provides guidance on the best use of vaccines to the Centers for Disease Control and Prevention (CDC) and U.S. Department of Health and Human Services (HHS).  Once ACIP recommendations have been reviewed and approved by the CDC and HHS, they are published in CDC’s Morbidity and Mortality Weekly Report (MMWR). The MMWR publication represents the final and official CDC recommendations for immunization of the U.S. population.


How is vaccine safety monitored after it’s been approved or authorized?

The FDA and CDC continue to closely monitor vaccine safety after the public begins using the vaccine. Both agencies have both longstanding and new safety systems in place for heightened monitoring of all COVID-19 vaccines. Learn more about the vaccine safety monitoring systems:  CDC’s V-SAFE is a new smartphone-based, after-vaccination health checker for people who receive COVID-19 vaccines. Vaccine recipients can opt-in to receive text messages and web surveys from CDC on how to report health problems following COVID-19 vaccination. The system will also provide telephone follow-up to anyone who reports medically significant adverse events. The report will be submitted to... Read More