Australian researchers have said they finally know what caused the blood clots linked to Covid-19 vaccines early on in the pandemic.
A “rare and severe” type of blood clot (vaccine-induced immune thrombotic thrombocytopenia) was detected in some people who had been given the Johnson & Johnson vaccine – authorised for emergency use by the US Food & Drug Administration in early 2021, nearly a year into the global pandemic – and the authorisation for that was later withdrawn.
Now, reports The Independent, Australian researchers say they finally know what happened with the J&J shot, as well as the similar Oxford-AstraZeneca vaccine in Europe.
People who developed the clots had a reaction to the virus used to make the shots, known as adenovirus, said the scientists. And they were genetically prone to the reaction.
“By modifying or removing this specific adenovirus protein, future vaccines can avoid this extremely rare reaction while continuing to provide strong protection against disease,” Flinders University researcher Dr Jing Wang said in a statement.
So, what happens?
When people get the shots, the body’s immune system can accidentally confuse a normal protein from adenovirus – which is used to ferry coronavirus DNA into our cells, leading to the creation of antibodies that protect us from the disease – with a protein found in the blood called PF4.
It’s this confusion that triggers the production of a dangerous blood antibody that leads to clotting, the researchers said. Known as an auto-antibody, it mistakenly attacks the host.
Building on years of previous research that examined PF4 and antibodies from vaccines, they found this out by using a mass spectrometer, which works to identify and quantify molecules within a sample.
“A novel aspect of the paper was our use of powerful mass spectrometry sequencing to identify molecular mimicry between the adenovirus vector protein and the PF4 culprit target,” Wang said.
“This was the missing link that explains how a normal immune response can, in very rare cases, become harmful.”
Nowhere to go but forward
The FDA and US Centre for Disease Control and Prevention (CDC) reported that 15 cases of VTT had been reported in 2021, in women aged between 18 and 59, after having the Covid vaccine, while hundreds of other cases were reported in Europe, although little data has been made available regarding cases reported elsewhere.
Some researchers have estimated a death rate for VITT of more than 20%.
For patients who have a very low platelet count and have experienced a brain haemorrhage after blood clots in the brain, however, the risk of death jumps to 73%, according to University College London.
But the new research can help to prevent this rare problem entirely, the Australians said.
“The findings will help ensure future vaccines built on this technology remain effective, accessible and even safer, particularly in regions where adenovirus‑vector vaccines are critical tools for disease prevention,” Flinders University wrote.
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