Australia's medicines regulator has confirmed the death of a 48-year-old woman from NSW's Central Coast was likely linked to the AstraZeneca vaccine.
The Therapeutic Goods Administration released a statement late on Friday evening that the woman was "admitted to hospital with an extensive thromboembolic event and thrombocytopenia (TTS) four days after receiving the AstraZeneca COVID-19 vaccine".
"Sadly, this person died in hospital and we extend our sincerest condolences to her family," the statement said.
The case is the first death in Australia likely linked to the vaccine and the third case of serious blood clots after receiving the vaccine, with the first two cases still in hospital.
Australia's regulators changed their advice about giving the AstraZeneca vaccine to people aged below 50 on Thursday April 8, but the woman was vaccinated earlier that day before the decision had been made.
"The review of this case was complicated by the patient's underlying medical conditions, including diabetes, some other medical conditions as well as some atypical features," the statement from the regulator, explaining the process undertaken by the Vaccine Safety Investigation Group, said.
"In relation to this case, VSIG agreed that the case was consistent with causal association to immunisation, although for this patient, anti-PF4 antibodies were absent. Anti PF-4 antibodies which activate platelets have been found in almost all other cases reported internationally of thrombosis (blood clots) with thrombocytopenia (very low platelets) associated with the AstraZeneca vaccine.
"Despite the atypical clinical features and the negative antibody test, in the absence of an alternative cause for the clinical syndrome, VSIG believed that a causative link to vaccination should be assumed at this time."
An autopsy will be conducted next week, and pending further results, the panel could change its decision.
At least 885,000 doses of the AstraZeneca COVID-19 vaccine had been administered in Australia so far, the regulator said, meaning the three known cases of blood clots represented a frequency of one in 295,000.
In the United Kingdom the frequency has been about one in 250,000.
Medical authorities this week nevertheless called on Australians over 50 not to cancel their bookings for the AstraZeneca vaccine.
Chief Medical Officer Paul Kelly told reporters in Canberra on Friday that "people should be cautious about jumping to conclusions" over the case and he urged people to continue to get vaccinated.
Prime Minister Scott Morrison said concerns regarding vaccine hesitancy meant it was important that the matter was fully investigated, while Professor Kelly confirmed some Australians had been reluctant to receive a vaccine since the AstraZeneca medical advice was updated.
"We have seen some hesitancy ... particularly in the state-run clinics," Professor Kelly said.
The clinics predominantly deal with healthcare and quarantine workers, many of whom are under 50.
However, the government's honesty would reassure many, Professor Kelly said..
"One of the crucial components about vaccine hesitancy, or the opposite vaccine certainty, is about understanding and knowing that if there is bad news, it's told," he said.
"That there is openness from people like myself."
That said, the virus itself poses a far greater risk in terms of blood clotting, he said, quoting a new Oxford University study.
The risk of developing blood clots in the brain is eight times more likely after a COVID-19 infection than an AstraZeneca vaccine, it found.
"Clotting is a feature of COVID," Prof Kelly said.
"It also happens to be a feature, very rarely, of the AstraZeneca vaccine.
"But the benefit absolutely, and particularly for those over the age of 50, outweighs significantly the risk."
NSW Premier Gladys Berejiklian on Friday morning said she would still enthusiastically line up for her second AstraZeneca dose.
"The vast majority of our citizens know the benefits of taking a vaccine - they also know the risks, as slight as it is," she told the Nine Network.
"I turned 50 last year and got the jab and am very excited to get the second one. The vast majority of our citizens want a vaccine, want to get ahead of it."
The federal government has appointed Commodore Eric Young to help coordinate the roll out of inoculations at the Department of Health's Vaccine Operations Centre.
The government will also have to consider the possibility of Australians needing a third Pfizer jab after the company's boss suggested it may be necessary to maintain virus protection.
- with AAP