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A clinical trial testing a COVID-19 vaccine

Learn more about the ENSEMBLE Study 

What is the ENSEMBLE COVID-19 Clinical Trial? 

This clinical trial, the ENSEMBLE trial, is being led by St. Jude and the University of Tennessee Health Science Center. Adults in the Memphis, Tenn. area who enrolled in the study received a COVID-19 prevention vaccine or a placebo.

The study closed to enrollment on Dec. 17, 2020.  On Feb. 21, 2021, the U.S. Food and Drug Administration issued an Emergency Use Authorization (EUA) for the single-dose COVID-19 vaccine in people 18 years of age and older.

The study showed the vaccine studied in the ENSEMBLE trial was 85 percent effective in preventing severe disease and preventing COVID-related hospitalization and death, beginning 28 days after vaccination.

Read about early trial results. 

There are many COVID-19 vaccine trials recruiting around the country. The study we are involved with is called the ENSEMBLE trial.

The ENSEMBLE trial will test the safety and effectiveness of a single-dose, investigational COVID-19 vaccine in adults.

This study is designed to test a single vaccine dose of an investigational COVID-19 vaccine compared with a placebo. The study includes about 45,000 adult volunteers, including many who are older than 60. St. Jude and the University of Tennessee Health Science Center recruited participants in the Memphis area for the study.

If you are a participant in the ENSEMBLE study, it is currently ongoing.  We thank you for participating, and encourage you to continue in the study. The EUA is based on the study gathering more data through your participation. A full approval is expected in 2021. If you have questions about your participation, email the study site at

Review Frequently Asked Questions about COVID-19 clinical studies.

To learn about future COVID-19 studies, register at


Before you join the study

You will be asked to fill out an online 5-minute survey to register for the study. You will be asked personal questions to determine if the study is a good match for you. If you are a match, someone will contact you and talk to you about the study and answer any questions you have. If you enter the study, you will get written information about the ENSEMBLE trial. You can talk with other people, like your family or doctor, and take as much time as you need to make the best decision for yourself about whether you want to join the study.

During the study

During the study, you will be asked about your medical history and for blood, saliva and nasal swab samples for necessary lab tests including for COVID-19. At the study site, you will get one injection in the arm, unless otherwise indicated. It will be either the investigational vaccine or a placebo, which is a liquid with no active ingredients. You will keep track of how you feel. Study staff will also be in contact to check on how you are feeling throughout the study.

You will not be exposed to COVID-19 as part of the study. You may still come into contact with the virus in your daily life.

If you develop symptoms of COVID-19 during the study, you will be tested. If you test positive, our study staff will monitor your daily diaries.

There are no costs to you to be in the study. If you are found eligible for the study, you can agree to be in the study now but can change your mind about participation at any time and for any reason.

After the study

When the study is over, we will share the results of the ENSEMBLE trial with you and members of your community, but the names of participants are never shared.

Register for future studies and begin the screening survey. Visit - NCT04505722 for additional details about the ENSEMBLE trial.