APRIL 2021

On April 13, 2021, the U.S. Centers for Disease Control and Prevention (CDC) and the Food and Drug Administration (FDA) jointly recommended a pause in the administration of the Johnson & Johnson (J&J) COVID-19 vaccine out of an abundance of caution after a rare, serious type of blood clot was reported in six women who received that vaccine. We will continue to monitor this situation and provide updates accordingly.

In light of this development, NATF still endorses vaccination with the two other COVID-19 vaccines that have received Emergency Use Authorization from the FDA. These six cases of blood clots are very rare, and the benefits of COVID-19 vaccination outweigh the risks of blood-clot-related side effects. Please see below for more information.

The North American Thrombosis Forum (NATF) strongly recommends that all adults get vaccinated against COVID-19, including:

  • People who have had a blood clot in the past
  • People with genetic clotting disorders (such as factor V Leiden) or who have a family history of blood clots 
  • People who take anticoagulation (sometimes called blood thinners)
  • People who take antiplatelet medications (aspirin, clopidogrel, ticagrelor)
  • People who have bleeding disorders such as hemophilias

Vaccination is the key to protecting our individual health and limiting the spread of COVID-19 in our communities. It’s also the best tool we have to prevent blood clots and other vascular complications associated with COVID-19, such as pulmonary embolism (PE), deep vein thrombosis (DVT), and stroke, as well as the chronic symptoms, called “COVID long-haulers syndrome,” which can persist indefinitely and be debilitating. 

What We Know:

  • Infectious diseases spread quickly within communities that have high numbers of unvaccinated people. As more people become vaccinated, disease transmission from person to person declines, which is known as herd immunity. When we achieve herd immunity, we protect the most vulnerable people in our society, including the elderly and those who have weakened immune systems.
  • The available COVID-19 vaccines are safe and effective. The U.S. Food and Drug Administration (FDA) has stringent standards that vaccine developers must meet. All vaccines that are distributed in the U.S. are rigorously tested in large clinical trials and continue to be monitored. [As mentioned above, the administration of the J&J vaccine has been paused as of April 13, 2021, due to six reported cases of rare but serious blood clots in patients who received that vaccine. Individuals are encouraged to contact their healthcare provider if they have received the J&J vaccine and have concerns.]
  • There is a proven link that being infected with COVID-19 increases the risk of having a blood clot. There is no proven link between the COVID-19 vaccines used in the U.S. and blood clots. [The six cases of rare blood clots that occurred in patients who received the J&J vaccine are currently being investigated.]
  • Even though more people are getting vaccinated, we must continue to wear masks in public, socially distance, and frequently wash our hands. 
  • Future research on COVID-19 vaccines should focus on:
    • COVID-19 variants, including the UK, South African, and Brazilian variants
    • The duration of protection 
    • Optimal timing of booster shots
    • Global health initiatives to support universal COVID-19 vaccination 

Disclaimer: This position statement reflects the consensus of the NATF Board of Directors and Medical Advisory Board and is based on the best available evidence. It is provided for informational purposes only and is not intended to serve as personalized medical advice. If you have specific questions or concerns about the vaccine, please consult your personal physician or healthcare provider.

NATF does not endorse or recommend one vaccine over another, nor do we endorse any one vaccine manufacturer and/or the products they distribute.  

NATF Executive Board

Samuel Z. Goldhaber, MD Associate Chief and Clinical Director, Cardiovascular Division, Brigham and Women’s Hospital (BWH)

John Fanikos, RPh, MBA Director of Pharmacy Business and Financial Services, Brigham and Women’s Hospital (BWH)

Jawed Fareed, PhD Director of the Hemostasis and Thrombosis Research Laboratories, Loyola University Medical Center

Gregory Piazza, MD, MS Section Head of Vascular Medicine and Staff Physician, Cardiovascular Division, Brigham and Women’s Hospital (BWH)

Christian T. Ruff, MD, MPH Director of General Cardiology, Cardiovascular Division, Brigham and Women’s Hospital (BWH)

Jeanine M. Walenga, PhD Co-Director of the Hemostasis and Thrombosis Research Laboratories, Loyola University Medical Center

NATF Medical Advisory Board

Brenda Shisslak Patient Representative

Alex Spyropoulos, MD System Director of Anticoagulation and Clinical Thrombosis Services, Northwell Health System

Aaron Aday, MD, MS Investigator, Vanderbilt Translational and Clinical Cardiovascular Research Center, Vanderbilt University Medical Center

Margaret Fang, MD, MPH Hospitalist, Research Director at the Division of Hospital Medicine, and Medical Director of the Anticoagulation Clinic, University of California San Francisco (UCSF)

Tzu-Fei Wang, MD, MPH Associate Professor of Medicine, Division of Hematology, University of Ottawa Ottawa, Canada

Jennifer Ballard-Hernandez, DNP Cardiology Nurse Practitioner, Tibor Rubin VA Medical Center and Cardiology Clinical Nurse Advisor to the Office of Nursing Services for VA Central Office

Tara Lech, PharmD Anticoagulation and Cardiovascular Clinical Pharmacy Specialist, Beth Israel Lahey Health


The Centers for Disease Control and Prevention; The Food and Drug Administration. Joint CDC and FDA statement on Johnson & Johnson COVID-19 vaccine. Updated April 13, 2021. Accessed April 13, 2021.

European Medicines Agency (EMA). Updated March 2021. Accessed March 2021.

The Centers for Disease Control and Prevention. Data and statistics on venous thromboembolism. Updated February 2020. Accessed March 2021.