Does the COVID-19 Vaccine Cause Blood Clots?
Apr 13, 2021

Last updated on May 12, 2021. We will continue to update this post as more information becomes available. 

Woman receiving a covid vaccine

Image from CDC via Unsplash

On April 13, 2021, the Food and Drug Administration (FDA) and Centers for Disease Control and Prevention (CDC) recommended a pause in the use of the Johnson & Johnson (Janssen) COVID-19 vaccine due to six reported U.S. cases of a rare and severe type of blood clot in combination with low levels of blood platelets in individuals after receiving the vaccine.

The reason for the pause was to give health experts the opportunity to investigate the reports further and alert healthcare providers and the general public about what was happening.

As more information became available, health experts determined two things: The risk appears to be extremely rare, and the benefits of the vaccine still outweigh the risks overall. 

Here’s what we know so far.

What’s the Risk? 

The combination of blood clots with low platelets (known as thrombosis with thrombocytopenia or TTS) reported after the Johnson & Johnson COVID vaccine is serious and concerning. It also appears to be extremely rare. 

Out of the roughly nine million people who have received the Johnson & Johnson COVID-19 vaccine in the U.S., 29 people have experienced the condition so far, mostly in women aged 18-49 years. One of those cases occurred during the clinical trial prior to authorization. Unfortunately, three women have died.

The risk of TTS varies by age and sex, but the latest estimates range from:

  • 4.7–12.4 per 1 million for women aged 18-49 years
  • 1.3–2.8 per 1 million for men aged 18-49 years
  • 1.3–2.7 per 1 million for men and women aged 50-64 years
  • <1 per 1 million for men and women 65+ years

For reference, health experts expect roughly 0.7-1.6 in 1 million people to experience clots with low platelets, regardless of vaccination.   

Blood clots can happen for a lot of reasons — including due to COVID-19 — but these rare cases can be tricky because they require a different type of treatment. Usually, heparin is administered to people experiencing blood clots, but that can be dangerous to people with these clots combined with low levels of blood platelets. For this reason, both the FDA and CDC, along with partners across the country, are working to alert healthcare providers about this difference in treatment and reminding them to report any adverse events after vaccination to VAERS and/or V-SAFE.

It should be noted that there are currently no concerns about this adverse effect in people who receive the Pfizer or Moderna COVID-19 vaccines.

How Do These Risks Compare to COVID-19? 

While these clots can be very serious, so can COVID-19. Over 550,000 people have died in the U.S. since the start of the pandemic. Many more have been hospitalized or have long-term health issues.

The individuals most at risk for the rare blood clots with low platelets after vaccination — that is, women 18-49 years old — aren’t the most likely to be hospitalized or die from COVID-19. But they do make up the bulk of new COVID-19 cases right now.

When health experts on the CDC’s Advisory Committee on Immunization Practices (ACIP) reviewed the data, they found that even for those most likely to experience this condition after getting vaccinated, the benefits of protecting themselves from COVID-19 still likely outweigh the risks associated with the vaccine.

That said, if you have a choice of what COVID vaccine to receive and you aren’t sure which to get, a doctor can help you better understand what the risks and benefits of each vaccine might be for you personally.

What Should You Do If You Received the Johnson & Johnson COVID Vaccine?

If you received the J&J COVID-19 vaccine within the last three weeks, please contact your healthcare provider or seek medical attention if you have:

  • Severe headache (especially one that starts 6+ days after vaccination)
  • Backache
  • New neurologic symptoms
  • Severe abdominal pain
  • Leg pain or swelling
  • Tiny red spots on the skin
  • New or easy bruising
  • Shortness of breath

Please note that it is common to experience mild to moderate flu-like symptoms, including fever, headache, fatigue and joint/muscle pain, during the first week after receiving any COVID-19 vaccine These common side effects usually start within three days of getting a vaccine and should only last a few days.

Everyone who received a COVID-19 vaccine — any COVID vaccine — should sign up for V-Safe – CDC’s After Vaccination Health Checker.

The Bottom Line…

This is a sign that the vaccine safety monitoring system is working well. It was able to find a rare, serious adverse event. It is only associated with the Johnson & Johnson (Janssen) COVID-19 vaccines, not the Pfizer or Moderna vaccines.

FDA and CDC have moved swiftly to save lives. Vaccinate Your Family will continue to share information on this situation as it develops.

In the meantime, learn more about COVID-19 and all of the COVID-19 vaccines on our website.


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NOTE: A version of this content originally appeared in Vaccinate Your Family’s Immunization Alerts eNewsletter, sent out on Friday, August 13, 2021. Stay up to date on the latest vaccine news by subscribing here....

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