Some researchers and medical specialists are calling for a review of the age groups who receive the AstraZeneca jab, after a 52-year-old woman died from a brain clot last week.Key points:The second Australian clotting death occurred after 3.6 million doses of AstraZeneca had been administeredThe rate of clotting incidents is 3.1 cases per 100,000 first doses for those aged under 50 and 1.8 cases for those who are olderFor people aged 50-59, the rate of clotting is 1.9 cases for every 100,000 doses"It may be time to consider now that we do offer Pfizer vaccine for the 50 to 59-year-old age group," said associate professor Margie Danchin, a clinician who researches vaccine risk perception.Dr Danchin wants to see the age cut-off for AstraZeneca reviewed after the latest death from a condition known as thrombosis with thrombocytopenia syndrome (TTS)."I think in Australia now, with such low rates of COVID disease, the death of a previously well 52-year-old woman definitely asks us to reconsider the age threshold for the recommendation for AstraZeneca vaccine," she said.The woman's death, the second believed to be linked to the vaccine in Australia, occurred after 3.6 million doses of AstraZeneca had been administered.Stay up-to-date on the coronavirus outbreakLast week, Chief Medical Officer Paul Kelly called for perspective."I will point out this remains an extremely rare event to get these serious clots," he said.Margie Danchin says people should look out for symptoms like headaches, blurred vision or abdominal pain anywhere between four and 30 days after getting the vaccine.(Supplied: Murdoch Research Institute)"But when they happen, as we have seen in this case, it can have tragic circumstances."Currently the rate of clotting incidents is low, at 3.1 cases per 100,000 first doses for those aged under 50, and 1.8 cases for those who are older.For people aged 50-59, the rate of clotting is 1.9 cases for every 100,000 doses.Adjunct professor John Skerritt, head of the medicine regulator the Therapeutic Goods Administration, said clotting deaths were extremely rare.Read more about Australia's vaccine rollout:"This condition seems to be manifesting in a serious and less serious form," he said."And while there are a number of serious cases, the encouraging thing is that the majority of the cases are the less serious form."How do I know if I have a blood clot?About one in every 250,000 people given the AstraZeneca vaccine in Europe have developed blood clots, but what are the symptoms of this rare phenomenon?Read moreThere have been 48 confirmed and probable cases of TTS in Australia, 15 of which were more serious clots in the brain and abdomen. Thirty-three were more typical clots found in the legs and lungs.But blood clotting specialist professor Huyen Tran said the incidence rate of the clotting condition was only part of the picture, and the severity of the cases must be considered.Professor Tran cited international research which showed age was a factor in the severity of the clotting syndrome's disease."It appears from the data coming out of Europe and in the UK, the more severe cases of [the clotting syndrome] certainly involve younger people under the age of 60," he told 7.30."We need to look closely at the rate between the age of 50 and 59 and, in addition, the severity of the episodes that are occurring."This may affect the policymakers' decision to change who should receive the AstraZeneca vaccine."Professor Tran is a member of the Thrombosis and Haemostasis Society of Australia and New Zealand, which is investigating vaccine-induced clotting cases.He has been involved in nearly every Victorian case, and echoed the need to reconsider the current age cut-off for AstraZeneca."Personally, I do have concerns about looking very carefully at needing to move the age up to 60," he said.The Australian Technical Advisory Group on Immunisation (ATAGI) currently recommends AstraZeneca only for people aged over 50.Here's what you need to know about COVID-19 in Australia:The decision to limit its use came after several European nations suspended their use of AstraZeneca following cases of the vaccine-induced clotting syndrome.Many countries then amended their advice, to say that AstraZeneca only be used in specific age groups.The UK recommended it only be used for those aged over 40, Italy chose over 55, and Sweden went with an age threshold of over 65.Australians over 50 'should be confident' in the vaccineBut TGA head Professor Skerritt is standing by the current age threshold.Professor Skerritt says the risk of severe clotting from the vaccine is still very rare.(ABC News)"When you look at the frequency of the syndrome known as TTS, it's still much more common in the under-50s than the over-50s," he said."That was one of the factors behind the recommendation to government."Professor Skerritt said people aged 50 to 59 should be assured of the safety of AstraZeneca for their age bracket."They should be confident that 50 has been set as the appropriate age for which for benefits of vaccination significantly exceed the risks," he said."If the risk changes, then the advice to government will change accordingly."How do I know if I have a blood clot?About one in every 250,000 people given the AstraZeneca vaccine in Europe have developed blood clots, but what are the symptoms of this rare phenomenon?Read moreWhile policymakers consider the latest death from TTS, Professor Tran said cases that were detected early could be effectively treated."Once we have the diagnosis, we can treat this condition pretty well," he said.Dr Danchin said symptoms to be aware of included headaches, blurred vision or abdominal pain anywhere between four and 30 days after getting the vaccine."If people are able to seek medical help early and have treatment initiated with a blood product called immunoglobulin and blood thinners, then they can have a very good outcome,' she said.What you need to know about 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