A pulmonary embolism (PE) is a blood clot that breaks off from a deep vein and travels to a lung artery, where it blocks blood flow. PE is a serious, potentially life threatening condition.

In May 2022, the Food and Drug Administration (FDA) limited the authorized use of the Johnson & Johnson (J&J) COVID-19 vaccine due to reports of a blood-clotting disorder called thrombosis with thrombocytopenia syndrome (TTS).

TTS can occur in many different places throughout the body. It often affects the brain or stomach, but it can also affect the pulmonary arteries.

While very rare, this vaccine side effect can cause a pulmonary embolism. Keep reading to learn more.

Know the terms

The emerging data on this condition is still new. Scientists use several terms to describe the condition, including:

  • thrombosis with thrombocytopenia syndrome (TTS)
  • vaccine-induced immune thrombotic thrombocytopenia (VITT)
  • vaccine-induced prothrombotic immune thrombocytopenia (VIPIT)

Whether TTS is the same as VITT and VIPIT or if they’re similar conditions on the same spectrum requires further evaluation.

In this article, we’ll use TTS to describe the condition.

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Thrombosis with thrombocytopenia syndrome (TTS) is a new clinical syndrome and rare complication of the J&J COVID-19 vaccine. It’s also a rare complication of the Vaxzevria (AstraZeneca) vaccine, used outside the United States. Researchers don’t yet know the exact mechanism that causes TTS to occur.

The FDA originally authorized the J&J vaccine for emergency use in February 2021. Over the first 13 months, the Vaccine Adverse Event Reporting System received reports of 60 confirmed cases of vaccine-induced TTS in people who received the J&J vaccine. Of those, nine died as a result.

Millions of people have gotten the J&J vaccine without experiencing TTS or other severe side effects. The FDA estimates that the reported rate of TTS occurrence after J&J vaccination is 3.23 for every million doses. The reported rate of death from TTS after J&J vaccination is 0.48 per million doses.

J&J and AstraZeneca are adenoviral vector (carrier) vaccines. The way vector vaccines fight SARS-CoV-2, the virus that causes COVID-19, is different from how messenger RNA (mRNA) vaccines work. Pfizer-BioNTech and Moderna are both mRNA vaccines.

TTS may also be caused by mRNA vaccines, but at a far lower rate than those caused by adenoviral vector vaccines.

TTS is rare, but blood clots are not. Not every blood clot after vaccination will be due to the vaccine. Doctors also refer to pulmonary embolism and deep vein thrombosis as venous thromboembolism (VTE).

According to the Centers for Disease Control and Prevention (CDC), 900,000 people in the United States experience VTE annually. About 1 in every 9 of those people die as a result.

There are no clear markers that specifically indicate who will get vaccine-induced PE and TTS. Research into TTS found that most people affected had transient (non-lasting) anti-PF4 antibodies in their systems. Those antibodies activate platelets, which help your blood clot.

According to a review of studies, potential risk factors for TTS may include being genetically female and being under 60. Most reported cases have occurred in females ages 30 to 49.

But research hasn’t definitively proven these risk factors. For example, a 2021 study on TTS cases from the AstraZeneca vaccine found a median age of 48 years and no bias regarding gender and sex at birth. More research is needed.

According to Healthdirect Australia, having any of these conditions may potentially increase your risk:

Vaccine-induced TTS risk factors differ from risk factors for PE not caused by COVID-19 vaccination.

The health risks associated with getting COVID-19 far outweigh the risk of getting TTS from a vaccine. In addition to severe respiratory illness and other issues, blood clots are a potential side effect of the virus itself.

Currently, the J&J vaccine is recommended only to people who’ve had a severe allergic reaction to an mRNA vaccine (anaphylaxis) and those who don’t want or can’t find an mRNA vaccine.

If you’re at risk for a pulmonary embolism, you should strongly consider getting an mRNA vaccine, such as Moderna or Pfizer.

Vaccine-induced TTS from mRNA vaccines is exceedingly rare. If you’re concerned about vaccine risks, talk with your doctor. They can guide you towards choosing the best vaccine for you.

Can COVID-19 cause pulmonary embolism?

Yes. COVID-19 can cause blood clots, even months after diagnosis. This may be due to lingering inflammation and other factors.

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Symptoms of TTS can start anywhere from 4 to 42 days after vaccination. If you experience any of these symptoms, call your doctor or go to an emergency department immediately:

  • intense or persistent headache that may be worse when you lay down
  • intense or persistent stomach pain
  • blurry vision
  • shortness of breath
  • trouble speaking
  • chest pain
  • swollen area in a leg
  • pinprick-sized blood spots under the skin away from the vaccination site
  • bruising easily

The symptoms of a pulmonary embolism are different from TTS and also require immediate medical attention. Symptoms of PE include:

  • chest pain
  • rapid or irregular heartbeat
  • shortness of breath
  • bloody cough
  • fever
  • swelling, pain, or warm feeling in one leg
  • discolored or clammy skin
  • excessive sweating
  • feeling dizzy or lightheaded

PE and TTS are treatable conditions, but early detection is key. Your doctor will likely perform blood tests, including a D-dimer test, and imaging tests, such as a CT scan, to determine your diagnosis.

Vaccine-induced thrombosis with thrombocytopenia syndrome (TTS) is a very rare blood clotting disorder caused by the J&J vaccine. TTS causes blood clots, including pulmonary embolism (PE), plus a low blood platelet count.

Even though the rate of vaccine-induced TTS is low, the FDA no longer recommends the J&J vaccine for most people.

The Moderna and Pfizer vaccines have an even lower incidence of TTS and PE after vaccination. The benefits of vaccination far outweigh the slight risk of TTS from these vaccines. Blood clots and other complications are much more likely to be caused by illness from COVID-19 than from the mRNA vaccines used to fight it.