ATAGI update following weekly COVID-19 meeting – 9 June 2021

An update from the Australian Technical Advisory Group on Immunisation (ATAGI) following their weekly meeting on 9 June 2021.

Date published:
General public

ATAGI met on Wednesday 9 June 2021 to review the latest developments relating to the AstraZeneca COVID-19 vaccine and Thrombosis and Thrombocytopenia Syndrome (TTS) cases in Australia and overseas.

ATAGI considered an update from the TGA on current confirmed cases and those under investigation. The latest TGA statement on TTS cases, including clinical outcomes, can be found here.

ATAGI examined estimates of risk of TTS by age group in Australia and note that there have been 35 confirmed cases reported and a further 13 are considered probable in around 2.5 million doses of COVID-19 Vaccine AstraZeneca given up to 25 May 2021.

Although estimates of risk based on small numbers of cases are imprecise, the risk of TTS is estimated in Australia at around:

  • 3.1 per 100,000 in those <50 years
  • 1.8 per 100,000 in those ≥50 years.

There were no significant differences in estimated risk by sex in those ≥50 years of age.

A breakdown of current rates by decade of age for those aged ≥ 50 years is included here:

Age bracket (years) Estimated rate (per 100,000 AZ vaccinations)











ATAGI discussed the case summary and clinical data of TTS cases. It was noted that TTS outcomes occur across a spectrum of severity from more mild cases, to cases with long term morbidity and can result in death, with two fatal cases recorded to date in Australia.

ATAGI also noted the TGA have reviewed Australia’s confirmed and probable TTS cases and those reported by overseas regulators using the recently proposed CDC Criteria, which uses the following categories:

  • Tier 1: criteria are defined as clots in an unusual location such as the brain or abdomen and a low platelet count with or without a positive test for antibodies that activate platelets (anti-PF4 antibodies)
  • Tier 2: criteria are defined as only clots found in more usual locations such as the legs or lungs with a low platelet count and a positive test for anti-PF4 antibodies.

When considering Australian TTS cases in using the recently proposed CDC Criteria, ATAGI noted in the Australian context:

  • 15 confirmed and probable TTS cases met the CDC Tier 1 definitions
  • 33 confirmed and probable TTS cases met the CDC Tier 2 definitions.

The smaller number of more severe Tier 1 cases likely reflect heightened clinical awareness in Australia, early case ascertainment and prompt diagnosis and effective treatment in Australia.

ATAGI emphasised that the ATAGI/THANZ joint statement on TTS and the use of the COVID-19 Vaccine AstraZeneca is an important resource. The statement provides updated information about TTS and reaffirms ATAGI’s previous advice regarding the safe use of the COVID-19 Vaccine AstraZeneca.

At this time, there is no update to the ATAGI statement from 23 April 2021 in relation to the use of the AstraZeneca COVID-19 vaccine.

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