Thrombosis with thrombocytopenia syndrome is a rare complication associated with COVID-19 vaccines.

Doctors use the term “thrombosis” to describe when a blood clot, or thrombus, forms and blocks a blood vessel. Sometimes this can limit blood flow to parts of the body, causing symptoms in the area the blood vessel supplies.

Thrombocytopenia is when a person has a low platelet count. Platelets are components in the blood that help with the immune response and with stopping bleeding from cuts and other wounds by causing the blood to clot. A low platelet count can lead to severe bleeding, even with minor injuries.

This article reviews the symptoms, causes, risk factors, and treatment of thrombosis with thrombocytopenia syndrome related to COVID-19 vaccines. It also discusses when someone should speak with a doctor.

A note about sex and gender

Sex and gender exist on spectrums. This article will use the terms “male,” “female,” or both to refer to sex assigned at birth. Click here to learn more.

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Vaccine-induced immune thrombotic thrombocytopenia (VITT) is a condition scientists first identified in March 2021. People may use the term “thrombosis with thrombocytopenia syndrome” to describe coincidental thrombosis and thrombocytopenia unrelated to vaccination, as well as VITT.

A person who develops the syndrome will have a blood clot along with an extremely low platelet count. While it is a rare side effect of COVID-19 vaccination, thrombosis with thrombocytopenia syndrome is a medical emergency, and people who develop it need rapid medical care.

Symptoms a person should be aware of and seek emergency medical attention for may include:

According to the American Society of Hematology (ASH), people should seek immediate medical attention if any of the following symptoms develop 4–42 days after vaccination:

However, the ASH also highlights that the incidence of this condition is extremely low, and the risk of death and severe outcomes of COVID-19 far outweigh the risk of VITT in relation to COVID-19 vaccines.

Common COVID-19 vaccine side effects

Common side effects of a COVID-19 vaccination are typically mild to moderate and may not occur in everyone.

They may include:

Certain COVID-19 vaccinations can, in rare cases, cause thrombosis with thrombocytopenia syndrome.

According to the ASH, both the Vaxzevria (AstraZeneca) and the Janssen (Johnson & Johnson) adenoviral COVID-19 vaccines are more likely to cause the syndrome than the Moderna or Pfizer mRNA vaccines.

Researchers first identified the syndrome in March 2021 following the administration of a COVID-19 vaccination.

According to the Melbourne Vaccine Education Centre, there are no clear diagnostic indicators for people who have a higher risk of developing thrombosis with thrombocytopenia syndrome.

It states that although people under 60 years old appear to be more at risk, there have also been cases in older adults. Some evidence also suggests the incidence may be higher in females. However, this may be because females have received more vaccine doses worldwide.

The center reports that there are currently no known medical conditions that may increase a person’s risk of developing the syndrome, including a history of blood clots.

Many healthcare organizations, such as the ASH and the Centers for Disease Control and Prevention (CDC), stress that the benefits of vaccination outweigh the risk of developing thrombosis with thrombocytopenia syndrome or other rare adverse events.

People should seek emergency medical treatment if they experience signs of the syndrome. Although it is a newly identified condition, specialists have identified treatments including:

A person should seek emergency medical attention if they develop symptoms associated with thrombosis with thrombocytopenia syndrome. Early detection and diagnosis can help improve outcomes and prevent complications.

The risk of developing thrombosis with thrombocytopenia syndrome is very low. The benefits of COVID-19 vaccination outweigh the possible risk of developing this syndrome or other possible complications that rarely occur.

A person with concerns about the safety of COVID-19 vaccines may find speaking with a doctor about them useful. A healthcare professional can discuss the potential side effects and the benefits of vaccination in further detail. They may also recommend getting one type of COVID-19 vaccine over another.

Thrombosis with thrombocytopenia syndrome is a rare complication that may occur following COVID-19 vaccination. The condition causes a person to develop a potentially life threatening blood clot and a low blood platelet count.

A person with the syndrome may present with several different symptoms, including trouble breathing, persistent headache, blurred vision, among others. People with any signs of thrombosis with thrombocytopenia syndrome should seek emergency medical attention by calling 911 as soon as possible.

Many health organizations state that the benefits of COVID-19 vaccinations outweigh the potential risk of developing thrombosis with thrombocytopenia syndrome or any other possible complications.