Three new Australian cases of rare blood clotting syndrome have been reported, but official health bodies maintain COVID-19 vaccination benefits still outweigh risks
A 35-year-old NSW woman, a 49-year-old QLD man and an 80-year-old Victorian man have been diagnosed with thrombosis with thrombocytopenia syndrome (TTS) after receiving the AstraZeneca COVID-19 vaccine.
Their symptoms began between nine and 26 days after vaccination.
Following a meeting to review the cases, the TGA’s Vaccine Safety Investigation Group (VSIG) concluded that all three cases were “very likely linked” to vaccination.
The news comes a week after the VSIG concluded that TTS in a 48-year-old woman who died in hospital was linked to receiving the AstraZeneca COVID-19 vaccine several days prior.
Five of six total cases of TTS across Australia are in people aged less than 50 years.
All are associated with the AstraZeneca COVID-19 vaccine, a viral vector vaccine, with none connected to the Pfizer vaccine, an mRNA vaccine.
To 22 April there have been about 1.1 million doses of AstraZeneca COVID-19 vaccine administered in Australia.
Similar cases of TTS have been reported in the US associated with the Johnson & Johnson (J&J/Janssen) vaccine, another viral vector vaccine.
Among the more than 8 million doses of the J&J/Janssen COVID-19 vaccine administered in the US as of 23 April, experts found 15 reports of women who later developed TTS.
All cases reviewed in the US occurred in women between 18 and 59 years old.
In response to the latest developments, the Australian Government has decided to restrict use the Pfizer vaccine for those aged under 50, with a few agreed exceptions, until general availability later in the year as supply increases.
The AstraZeneca vaccine will be offered to those aged 50 and over, and access to it will be brought forward to all people aged 50 and over from 17 May – or earlier, if supply is available.
Access from state-run clinics and respiratory clinics is expected from 3 May.
The Australian Technical Advisory Group on Immunisation (ATAGI) estimates that the overall rate of TTS is about 6 cases per million people vaccinated, but the rate is currently estimated to be higher (20-40 cases per million) in those under 50 years of age.
However it maintains that in people aged 50 years and over, the benefits of AstraZeneca COVID-19 vaccine outweigh the risks associated with vaccination.
“This is due to the ongoing potential for COVID-19 outbreaks, the widespread susceptibility of the Australian population, and the strong relationship of severe COVID-19 and mortality with increasing age,” said ATAGI.
The TGA agrees, stating that the risk for TTS appears lower in older adults.
“Although Australia has seen more cases of COVID-19 in the under 50s, hospitalisation and deaths data clearly demonstrate that the risk of serious harm from infection with COVID-19 remains much higher in over 50s, and the benefits of COVID-19 vaccination outweigh the risks,” said the TGA.
ATAGI continues to recommend that people who have received a first dose of AstraZeneca COVID-19 vaccine without serious adverse events can be given a second dose.
Current data suggest that the risk of TTS following a second dose is considerably lower than with a first dose, with one case reported from more than two million second doses given in the UK to 14 April 2021.