The U.S. Food and Drug Administration authorized Johnson & Johnson’s Covid vaccine for emergency use in February 2021, nearly a year into the global pandemic that would go on to kill more than one million Americans.
Just over two years later, the agency requested the voluntary withdrawal of the authorization, following cases of a “rare and severe” type of blood clot in people who had gotten the shot called “VITT.”
Now, Australian researchers say they finally know what happened with the shots and the Oxford-AstraZeneca vaccine in Europe.
The people who developed the clots had a reaction to the virus used to make the shots, known as adenovirus. 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 autoantibody, 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, an instrument that 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.”
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Nowhere to go but forward
The FDA and CDC reported that 15 cases of VITT had been reported in 2021, with all cases occurring in women between the ages of 18 and 59 years old.
They experienced symptoms between six and 15 days after receiving the vaccine.
And, hundreds of other cases have been 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 percent.
For patients who have a very low platelet count and have experienced a brain hemorrhage following blood clots in the brain, however, the risk of death jumps to 73 percent, according to University College London.
But the new research can help to prevent this rare problem entirely, the Australians say.
“Researchers say 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.
