COVID-19 and Blood Clotting

Getting your vaccine to prevent covid 19 and clottingLast Updated 9/9/2022

As COVID-19 has impacted communities across the United States, the National Blood Clot Alliance has monitored aspects of this novel coronavirus that intersect with the clinical interests of the clotting and clotting disorders community, including the Delta and Omicron variants.

Specifically, NBCA’s Medical & Scientific Advisory Board has been focused on the recognition of coagulopathies – or different types of blood clotting – that are being reported among people affected by COVID-19, particularly those who become severely ill after infection with the virus.

While research is ongoing and new studies emerge almost daily with new information, many questions remain about COVID-19. NBCA is sharing the resources below to help people better understand the relationship between COVID-19 and blood clots, as well as the use of the new vaccines and vaccine boosters for COVID-19. Individuals are encouraged, however, to always speak with their healthcare providers about all of their questions and concerns.

COVID-19 Vaccines 

vaccines protect against covid-19The first two vaccines for the prevention of COVID-19 were granted emergency use authorization (EUA) by the United States Food & Drug Administration (FDA) in December 2020, and administration of these new vaccines (Pfizer and Moderna) began across the country several days later in mid-December 2020. An additional vaccine received EUA from the FDA in February 2021, and administration of this vaccine (Johnson & Johnson) began in the U.S. shortly thereafter.

As the access to these COVID-19 vaccines expands, NBCA and its Medical & Scientific Advisory Board will monitor information that may be important for people affected by clots and clotting disorders, as well as those who are prescribed anticoagulation or “blood thinning” therapies.

Studies of the new vaccines against COVID-19 show that they are safe and effective and medical experts are recommending that people get vaccinated as soon as they can to prevent infection with the virus that causes COVID-19. People should speak with their healthcare providers about any questions they have about COVID-19 and the new vaccines being used to prevent infection with this highly contagious and very serious infectious disease.

To learn more about the three vaccines that are presently authorized for use in the United States, as well as those that are still being studied in clinical trials, visit the Centers for Disease Control and Prevention (CDC) website here: COVID-19 Vaccines. Also, visit CDC’s website to review the most frequently asked questions about the new vaccines here: Vaccine FAQs.

Click on the links below to learn more about:

COVID-19 Vaccine Boosters 

COVID-19 vaccination is recommended for everyone aged 5 years and older in the United States for the prevention of COVID-19. Vaccines are effective in preventing serious outcomes of COVID-19, including severe disease, hospitalization, and death.

Three COVID-19 vaccines are approved or authorized by the Food and Drug Administration:

  • Pfizer-BioNTech COVID-19 Vaccine
  • Moderna COVID-19 Vaccine
  • Johnson & Johnson (Janssen) COVID-19 Vaccine

Some COVID-19 vaccine recipients can get booster shots:  As eligibility guidance is rapidly being updated, please visit the CDC’s Vaccine Booster Eligibility Webpage for current approvals. As a booster dose, you may receive any of the COVID-19 vaccines authorized in the United States and are not limited to staying with the same brand as your original vaccination.

COVID-19 and Blood Clotting: Frequently Asked Questions 

telemedicine to discuss covid-19 and clottingThroughout the COVID-19 pandemic, NBCA has received numerous questions about the potential for clotting associated with COVID-19, as well as the use of the new COVID-19 vaccines.

While more information remains to be known and confirmed, we have compiled a list of Frequently Asked Questions (FAQs) to share the most current information available.

We will continue to update this resource as more information is made available, and your healthcare provider also may be able to help address your questions and share other resources.






如需下载为讲西班牙语的人翻译的这些常见问题解答的 PDF 版本,请点击这里:

Additional Public Health Resources about COVID-19 and Blood Clotting

Additional resources about COVID-19 and COVID-19 vaccines, including information that can help keep you and your family safe, is available from the Centers for Disease Control and Prevention:

COVID-19 Vaccination

research into covid-19 and clotting

COVID-19 Virus

This and other CDC guidance can be viewed here: CDC Website, COVID-19. In addition, individuals with questions can contact CDC’s general information help desk online or by phone at 1-800-CDC-INFO (1-800-232-4636) or by email at

You also can obtain important information from your local public health department. You can search for your local health department here: Directory of Local Health Departments.

NBCA Coronavirus Communications: COVID-19 and Blood Clotting

digital visits to mitigate against covid-19 and clottingClick on the links below to read more information about COVID-19 and blood clots shared by NBCA:

Clinical Trials

NBCA is committed to providing reliable, evidence-based, and impartial information to the clotting and clotting disorders community to help members of our community make the most informed decisions in consultation with their healthcare providers. COVID-19 has affected millions of people worldwide. The pandemic has devastated our country, communities, friends, and families in ways that will be felt for generations. It has also brought dramatic changes in science and medicine and how healthcare is approached. Clinical trials and vaccines are critical to saving lives and the future health of each of us. NBCA is pleased to provide you with evidence-based, unbiased information about possible participation in clinical trials and also COVID-19 vaccines for your discussion with your healthcare provider.

We hope you find this information useful. Let us know how we are doing with our educational materials by reaching out to us at We also encourage you to connect with us on social media for ongoing updates and new information. You can follow us on Facebook, Twitter, and Instagram.

Global Survey Documents Treatment Patterns to Prevent Blood Clots among Hospitalized Individuals with COVID-19

A group of clinicians and researchers – led by Rachel Rosovsky, MD, a hematologist at Massachusetts General Hospital, an Assistant Professor at Harvard Medical School, and a member of NBCA’s Medical & Scientific Advisory Board – recently conducted a global survey among more than 500 physicians from 41 different countries to document how healthcare providers are preventing, diagnosing, and treating blood clots in people with COVID-19. Below (right) is an infographic that visually depicts key findings from this survey. Information from this survey, published in the medical journal Research and Practice in Thrombosis and Haemostasis, shows:

  • graphic about covid-19 and clottingThe majority (78 percent) of the survey respondents reported that they recommend prophylactic (intended to prevent disease) anticoagulation therapy to help prevent blood clots from forming in individuals hospitalized with COVID-19. There was a wide variation in practice when respondents were asked in what situations they would increase the dose of anticoagulation.
  • Bleeding, a potential side effect of any anticoagulation therapy, was addressed by most (73 percent, n=377) of the survey respondents, with more than half (54 percent) of this group reporting that they saw no bleeding, about one-third (34 percent) reporting minor bleeding, and smaller numbers of respondents reporting clinically relevant bleeding (14 percent) or major or potentially life-threatening bleeding (12 percent).
  • Most (75 percent, n=391) of the survey participants responded to questions about using compression ultrasound (a medical imaging technique that involves the placement on the skin of a probe that uses soundwaves to construct an image of tissue beneath the skin to determine if a clot may be present) to diagnose a deep vein thrombosis (DVT, or blood clot in the leg or arm) among people affected by COVID-19. Specifically:
    • 80 percent of this group reported that they obtained compression ultrasound DVT symptoms only if a patient had symptoms of a DVT
    • 17 percent recommend compressional ultrasound if a patient had an elevated D-dimer (a blood test that may indicate if a person has elevated levels of the D-dimer protein fragment that remains after a clot forms)
    • 8 percent recommended compression ultrasound in all hospitalized patients who were critically ill and in the intensive care unit (ICU)
  • A portion (44 percent) of the survey respondents shared their estimates for the potential incidence of clotting among patients hospitalized for COVID-19, with estimates ranging from as low as 1 percent up to 50 percent, with higher numbers in ICU than among all hospitalized patients.

The group of medical experts who conducted this survey stress the urgent need for both well-designed studies to help the medical community understand the incidence and risk factors for blood clots among people affected by COVID-19, as well as randomized clinical trials to address the use of anticoagulation therapies among these same individuals.

Healthcare professionals (HCPs) can track global updates relative to COVID-19, using the interactive map created and maintained by Johns Hopkins University here: Johns Hopkins COVID-19 Dashboard. (Reference: Dong E, Du H, Gardner L. An interactive web-based dashboard to track COVID-19 in real-time. Lancet Infect Dis; published online Feb 19, 2020.)

In addition, HCPs can review guidance from the Anticoagulation Forum here and the American Society of Hematology here.

Risk Factors, Signs and Symptoms

Now more than ever, it’s crucial to understand the risk factors for blood clots, and also the signs and symptoms that might signal you need to seek medical attention.

additional risks for clotting other than covid-19

symptoms of clotting











Learn more about blood clot risk factors here: Risk Factors

Learn more about blood clot signs and symptoms here: Signs and Symptoms

Episode 1: Covid-19 Treatment Options for Blood Clot Patients on Anticoagulants

Learn more about Covid-19 treatment options for blood clot patients on anticoagulants. This mini PEP Talk session is joined by special guest and NBCA Medical and Scientific Advisory Board Member, Dr. Caroline Cromwell, a hematologist and the Director of Thrombosis Services at Mt. Sinai Medical Center in New York City.

Healthcare Professionals: Our Best Resources

doctors treating covid-19 and clottingThe information provided here is not intended to serve as a substitute for professional medical advice. Please talk to your physician or medical team about any questions you have concerning your health or COVID-19 and clotting.

If you need help in finding a second opinion or medical expert in your local community, you can use one of the search tools at the following link to identify medical experts in your local community: Find a Doctor.



Additional NBCA Resources