A new study has found two Covid vaccine side-effects which can attack the heart, brain and spinal cord.
Researchers at the Global Vaccine Data Network discovered links between mRNA(Pfizer and Moderna) vaccines and myocarditis - inflammation of the heart muscle - and pericarditis - swelling of the thin sac covering the heart.
Experts stress that the new side-effects are "exceptionally rare" and the benefits of Covid vaccines still "vastly outweigh the risks".
The study of more than 99 million people also confirmedGuillain-Barré syndrome, when the immune system attacks the nerves and cerebral venous sinus thrombosis, a type of blood clot in the brain as rare side effects associated with the AstraZeneca vaccine.
The international journal Vaccine, where the new data is published, also established that acute disseminated encephalomyelitis - an inflammation and swelling in the brain and spinal cord - was also linked to the AstraZeneca vaccine.
A new study has found two very rare Covid vaccine side-effects which can attack the heart, brain and spinal cord
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The study involved people from Australia, Argentina, Canada, Denmark, Finland, France, New Zealand and Scotland.
Researchers say the results were based on electronic healthcare data, which compared the rates of 13 brain, blood and heart conditions in people after they received the Pfizer, Moderna or AstraZeneca vaccine with the rate that would be expected of those conditions in the population before the pandemic.
The new discovery of acute disseminated encephalomyelitis triggered researchers to independently confirm the side-effect by carrying out a second study.
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Prof Jim Buttery, co-director of the Global Vaccine Data Network said the second study included a separate dataset of 6.8 million Australians who were injected with the AstraZeneca vaccine.
The Australian study of AstraZeneca-specific data confirmed acute disseminated encephalomyelitis as a side-effect but also helped detect a second new rare side-effect, known as transverse myelitis - spinal cord inflammation.
According to Vaccine, the risk of acute disseminated encephalomyelitis is found in 0.78 cases for every million doses, while transverse myelitis appears in 1.82 cases per million doses.
The risk of myocarditis is even higher with natural Covid infection than it is following a vaccination, Buttery said.
The new discovery of acute disseminated encephalomyelitis triggered researchers to independently confirm the side-effect by carrying out a second study
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The senior research analyst at the Murdoch Children’s Research Institute in Australia added that despite the conditions being serious, patients usually recover from them.
Prof Julie Leask, a vaccine expert at the University of Sydney said it is important to note that a Covid infection increases the risk of some of the rare conditions "much more than a vaccine" does.
She said the studies show that: “Our vaccine experts are paying attention to when vaccines lead to serious side-effects, and they’re acting on it.
"Being confident in a system that will detect problems and address them, is a very important part of a robust vaccination program."