COVID-related blood clots have been linked to a mystery, according to researchers -experts advise caution

A German study team has proposed a possible approach to prevent the uncommon, life-threatening blood clots caused by two of the most widely used COVID-19 vaccines, but other scientists say it's too early to draw any conclusions about the mechanism behind the potentially fatal condition.

Despite this, the authors of the new preprint paper anticipate that their theory may eventually aid laboratories in adapting the AstraZeneca-Oxford and Johnson & Johnson vaccines to improve safety and potentially expand worldwide vaccination efforts.

Vaccine-induced immunological thrombocytopenia (VITT) is far more serious than a conventional blood clot because it can cause cerebral venous sinus thrombosis (CVST), which causes occlusion of the veins that drain blood from the brain and can result in catastrophic hemorrhage.

The difficulty, according to the German researchers, is in the delivery strategy of these two comparable vaccines, which both use adenovirus vector technology to transfer genetic instructions into cells to generate the coronavirus spike protein.

The findings, which were published online on Wednesday but have yet to be peer-reviewed, state that this sort of vaccine sends the spike protein's DNA gene sequence directly into the cell's nucleus, where some regions of the spike protein DNA may be spliced or split apart.

The research, which was based on the team's own lab work with the widely used HeLa human cell line, suggests that these "undesirable" breakdowns can lead to mutations in the spike protein DNA, making it more difficult for those proteins to bond to the cell, allowing them to secrete into the body and potentially triggering "inflammatory reactions" that can lead to rare blood clots.

Three phases, according to the researchers, are at work: The scientists noted that rogue spike proteins in the bloodstream, paired with newly developed antibodies meant to fight them, as well as highly particular blood flow conditions in veins draining from the brain, "may result in the uncommon but severe occurrences after immunization."

The Public Health Agency of Canada (PHAC) now predicts that the rate of VITT in Canadians who received the AstraZeneca vaccination is between 1 in 83,000 and 1 in 55,000, with a fatality rate of 20 to 50%, but this estimate is susceptible to change as more data becomes available. PHAC said in a statement on Thursday that out of two million doses administered, there have been 27 confirmed cases of VITT in Canada, with five deaths among them.

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