Information for Immunisation Providers on Thrombosis with Thrombocytopenia Syndrome (TTS) following COVID-19 vaccination
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Information for Immunisation Providers on
Thrombosis with Thrombocytopenia Syndrome
(TTS) following COVID-19 vaccination
15 September 2021 – Version 5
What has been updated:
The newly registered Spikevax (Moderna) COVID-19 vaccine has been included in this advice.
Thrombosis with thrombocytopenia syndrome (TTS)
On 8 April 2021, the Australian Government received advice and recommendations from the
Australian Technical Advisory Group on Immunisation (ATAGI) regarding a link between the
Vaxzevria (AstraZeneca) and a rare new adverse event called thrombosis with
thrombocytopenia syndrome (TTS).
On 17 June 2021, ATAGI issued a statement recommending Comirnaty (Pfizer) as the preferred
vaccine for those aged 16 to under 60 years. This updates the previous preferential
recommendation for Pfizer over AstraZeneca in those aged 16 to under 50 years. The
recommendation was revised due to a higher risk and observed severity of TTS related to the
use of AstraZeneca observed in Australia in the 50-59 year old age group than reported
internationally and initially estimated in Australia. ATAGI is meeting weekly to review emerging
data on TTS and providing weekly updates. To keep up to date visit www.health.gov.au/news.
Pfizer or Moderna are the preferred vaccines for those aged under 60 years. Pfizer and
Moderna are registered for use in people aged ≥12 years.
What is thrombosis with thrombocytopenia syndrome (TTS)?
This is a very rare adverse event causally linked with AstraZeneca.
It involves thrombosis with thrombocytopenia, with onset of symptoms occurring around 4 to 42
days (most commonly 4 to 30 days) following vaccination with AstraZeneca. The sites of
thrombosis in reported cases are unusual, varied and usually venous. Most cases reported to
date have included cerebral venous sinus thrombosis (CVST) or thrombosis of the splanchnic
(abdominal) circulation. Although very rare, TTS can cause disability and even death, with a
fatal outcome in about 17% of the cases reported in the UK.1 The overall case fatality rate in
Australia is lower than reported internationally. This is likely to reflect increased detection due to
heightened awareness, as well as early diagnosis and treatment. A spectrum of severity of
1
illness has been reported in Australia, from fatal cases and those with significant morbidity, to relatively milder cases. No biological or other risk factors have been identified that predict who will develop TTS. It appears to be an idiosyncratic reaction. Cases have been reported in all ages and in both men and women. TTS appears to be more severe in younger people. In Australia, the rate of TTS is estimated to be about 1-2 per 100,000 vaccinated with AstraZeneca. For those under 60 years of age, the rate is estimated to be higher, about 2-3 per 100,000 people. These estimates will be updated as further information become available. So far, almost all reported cases of thrombosis with thrombocytopenia syndrome have occurred after the first dose of AstraZeneca. UK data suggests that the risk of TTS is much lower after the second dose, with 44 cases reported to date out of 22.8 million second doses of the AstraZeneca COVID-19 vaccine given. This translates into an estimated rate of 1.9 case per million second doses (compared to a reported risk of 14.8 cases per million first doses in the UK). Pfizer vaccine and Moderna are not associated with TTS. What is the ATAGI advice? 1. Pfizer and Moderna vaccines are preferred over AstraZeneca in people aged
age should strongly consider AstraZeneca if they are unable to access Pfizer or Moderna
vaccines. For more information refer to the ATAGI statements on use of COVID-19 vaccines in
an outbreak setting published on 13 July 2021 and 24 July 2021.
Counselling patients
Anyone 18 years and over can decide to have the AstraZeneca vaccine, with informed consent.
The Department of Health has published a patient information sheet on TTS, which patients
should be encouraged to read before vaccination with AstraZeneca. The following guide will
assist patients and providers to assess the benefits against risks of harm of vaccination for
people of different ages: Weighing up the potential benefits against risk of harm of
AstraZeneca.
FAQs
1. What are the benefits and risks of vaccination with AstraZeneca Vaccine for my
patient?
The benefits of vaccination with AstraZeneca are greater for some people, such as older
adults (>60 years), people who have an increased risk of exposure to COVID-19 (e.g.
through their occupation or upcoming overseas travel), and people who have medical
comorbidities that increase their risk of severe illness from COVID-19.
No medical risk factors for TTS have been confirmed. Younger adults appear to have a
higher risk of TTS compared to older adults. There is a theoretical concern that the risk of
TTS may be higher in people with a past history of cerebral venous sinus thrombosis
(CVST) or heparin induced thrombocytopenia (HIT) idiopathic splanchnic (mesenteric,
portal, splenic) vein thrombosis or antiphospholipid syndrome with thrombosis.
2. What should I advise people with a history of blood clots or clotting tendencies?
The risk of TTS is not likely to be increased in people with the following conditions, and
people in these groups can receive AstraZeneca:
o History of blood clots in typical sites
o Increased clotting tendency that is not immune mediated
o Family history of blood clots
o History of ischaemic heart disease or stroke
o Current or past thrombocytopenia (low platelet count)
o Those receiving anticoagulation therapy
Reassuringly, in countries where AstraZeneca has been extensively used, there does not
appear to be an increased occurrence of other clotting conditions (i.e. thrombosis
unaccompanied by thrombocytopenia) following vaccination.
Pfizer and Moderna are the recommended vaccines for people at any age with a history of
cerebral venous sinus thrombosis (CVST) or heparin induced thrombocytopenia (HIT)
idiopathic splanchnic (mesenteric, portal, splenic) vein thrombosis or antiphospholipid
syndrome with thrombosis, because of theoretical concerns that these conditions may
3increase their risk of TTS. ATAGI will continue to monitor evidence on TTS and will update
its advice if any new risk factors are identified.
3. If my patient chooses to go ahead with AstraZeneca vaccine, what should we look
out for?
Refer patients to the list of symptoms to monitor for, provided in the patient information
sheet on TTS, summarised in the section below. Patients should be advised to present for
medical advice if they develop any persistent symptoms after vaccination. Patients should
be advised the onset of TTS is around 4 to 42 days following vaccination.
4. What else should I consider?
Some additional benefits of vaccination can be considered when counselling patients
• The potential indirect benefit of vaccination to others, e.g. household members who
have risk factors for severe COVID-19.
• The ongoing potential for new incursions of SARS-CoV-2 into Australia, which could lead
to new outbreaks.
• The potential for a delay in accessing an alternate brand of COVID-19 vaccine.
As with any vaccine, consent should be recorded by the vaccine provider.
Identification and referral of suspected cases
Primary care providers should also refer to the Primary Care Approach to Thrombosis with
Thrombocytopenia Syndrome (TTS) after AstraZeneca
Any patient with concerning signs or symptoms potentially related to TTS following receipt of
AstraZeneca should be referred to an emergency department for assessment and investigation,
including consultation with a haematologist. Based on reported cases to date, the timing of
greatest risk is around 4 to 42 days after vaccination.
Concerning signs or symptoms include:
• Headache that persists beyond 48 hours after vaccination, or appears later than 48
hours after vaccination where simple analgesia may alleviate headache initially, but it
persists, may be worse when lying down or may be accompanied by nausea and
vomiting
• Signs and symptoms of raised intracranial pressure or focal neurological deficits or
seizures
• Signs or symptoms suggestive of thrombosis in other anatomical locations
(e.g. abdominal pain suggestive of thrombosis in the splanchnic circulation, or chest pain
suggestive of pulmonary embolism)
• Signs suggestive of clinically significant thrombocytopenia, such as petechial rash or
bleeding, or bruising not at the vaccine injection site that cannot be explained
Blood clots such as DVT or PE occur commonly in the population in the absence of vaccination,
at an annual rate of about 1 per 1000 people. Some of the blood clots that occur will
coincidentally be after receiving the AstraZeneca COVID-19 and not causally related to the
4vaccine. Providers should refer to clinical guidance from the Thrombosis & Haemostasis
society of Australia and New Zealand (THANZ) on investigation and management of anyone
who presents with the above symptoms suggestive of thrombosis with thrombocytopenia after
vaccination and seek expert haematologist input as needed.
Initial investigations should include:
• Full blood count (to look for thrombocytopenia)
• D-dimer (typically ≥ 5 X upper limit of normal)
• Fibrinogen (can be lower than expected)
• Imaging as clinically indicated (for example brain CT or MRI for CVST).
If screening tests suggest thrombosis with thrombocytopenia (low plateletsYou can also read
