What is thrombosis with thrombocytopenia syndrome?

Thrombosis with thrombocytopenia syndrome (TTS) is a very rare syndrome. It occurs when a person has blood clots (thrombosis) together with a low platelet count (thrombocytopenia). It's also referred to as 'vaccine-induced immune thrombotic thrombocytopenia' (VITT).

Thrombosis is the formation of a blood clot, which can reduce normal blood flow in an affected blood vessel.

Thrombocytopenia is a condition where there aren't enough platelets in the blood. Platelets normally help the blood to clot (clump), which stops you from bleeding excessively (for example, if you cut yourself).

How are TTS and blood clots linked to the AstraZeneca vaccine?

TTS is a very rare side effect that was seen in some people after getting the AstraZeneca COVID-19 vaccine. The AstraZeneca COVID-19 vaccine is no longer available in Australia.

The risk of TTS appears to have been slightly higher in people younger than 60 years of age.

The blood clots can occur in different parts of the body, including:

• the brain (called cerebral venous sinus thrombosis, or CVST)
• the abdomen (splanchnic vein thrombosis)
• the lungs (pulmonary embolism)
• limb veins (deep vein thrombosis (DVT))
• arteries (arterial thrombosis)

The process that causes TTS is not fully understood. It is thought to be similar to heparin-induced thrombocytopenia (HIT). This is a rare reaction to a medicine called heparin that affects how platelets work.

What are the symptoms of thrombosis with thrombocytopenia syndrome?

Symptoms of TTS affecting the brain included:

• severe, persistent headache
• blurred vision
• difficulty speaking
• drowsiness
• seizures or confusion

Symptoms of TTS affecting the rest of the body included:

• difficulty breathing
• chest pain
• leg swelling
• persistent abdominal (stomach) pain
• tiny blood spots under the skin, away from the site of injection

Symptoms occurred between 4 and 42 days after vaccination with the AstraZeneca COVID-19 vaccine.

Are there any risk factors for TTS?

No medical conditions were found to increase your risk of developing TTS after vaccination.

The risk of TTS was higher in young people, and young women often experienced a more severe form of TTS.

The risk of TTS was lower after the second vaccine dose than the first.

How is TTS diagnosed and treated?

Some people with TTS were very unwell and needed to go to hospital straight away for treatment. If a clot in the brain was suspected, patients were referred to an emergency department for urgent investigation.

TTS was diagnosed using blood tests and scans including CT scans.

Treatment for TTS included:

• anticoagulant (anti-clotting) medicines (other than heparin)
• intravenous immunoglobulin (IVIG) — infusion of a blood product containing antibodies
• high dose prednisone — a type of steroid medicine

What are the complications of TTS?

The main complication of TTS included blood clots that could occur in different locations around the body.

Resources and support

• Speak to your GP. If you don't have a regular GP, you can find one near you using the healthdirect Service Finder.
• Read more about COVID-19 vaccines. For general information on COVID-19, visit the healthdirect COVID-19 hub.
• See the Australian Government Department of Health's patient information fact sheet on AstraZeneca vaccine and TTS.
• Get up-to-date information on vaccines and report side effects on the Therapeutic Goods Administration's (TGA) website.

Do you prefer to read in languages other than English?

• The NSW Multicultural Health Communication Service has a glossary of vaccination terms in many different languages.