The Medicines and Healthcare Regulatory Agency said the risk associated with this type of blood clot is "very small" and that the public should continue to take up the vaccine when offered it.
News of the deaths came as several European countries as well as Canada suspended the use of the vaccine for certain age groups over thrombosis fears.
The Australian case, first reported on April 2, is now being investigated by the country's Therapeutic Goods Administration.
"It is a complaint "against X", because we have no element against a named person for manslaughter", said Boittin, adding that this "classification can evolve" as the case develops.
But, he said, "The key thing to remember is how rare these brain clots are, and how powerful the proven benefit of vaccination is against COVID".
However, he said the risks of taking the AstraZeneca vaccine are still far outweighed by the risks of not getting the jab.
In reporting its updated case count, Britain's medicines regulator said that "the benefits of the vaccines against COVID-19 continue to outweigh any risks, and you should continue to get your vaccine when invited to do so".
"Receiving the vaccine is by far the safest choice in terms of minimizing individual risk of serious illness or death", he said.
Australian health experts are investigating whether a man's "extremely rare" blood clot condition is linked to the AstraZeneca vaccine.
The woman, a social worker, who was vaccinated in mid-March due to her work at a centre with disabled people - did not suffer from any particular health problems, added Boittin.
There were no reports of people who had the Pfizer/BioNTech suffering from blood clots.
"These are expected and not of concern unless severe or persistent", he said.
United Kingdom drug regulators say the AstraZeneca COVID-19 vaccine remains safe.
More than 31 million people have received a first coronavirus vaccination dose in Britain, which is using both the AstraZeneca vaccine and the BioNTech-Pfizer version.