Interesting read on the vaccines and blood clots. There's something about the spike protein in both the vaccine or with a Covid-19 infection that can cause blood clots in some people, they still don't quite understand what is going on.
https://www.nature.com/articles/d41586-021-02291-2Then there’s the spike protein itself. One team of researchers wondered whether the antibodies that bind to PF4 in people with VITT are an unintended by-product of the body’s immune response to spike. But they found that the PF4 antibodies can’t bind to it, suggesting that they are not part of the immune response to the viral protein9.
But cancer researcher Rolf Marschalek at Goethe University Frankfurt in Germany and his colleagues have shown that the snippets of RNA that encode spike can be cut apart and stitched back together in different ways in human cells; some of these forms, called splice variants, can generate spike proteins that get into the blood and then bind to the surface of cells that line blood vessels10. There, they cause an inflammatory response that is also seen in some SARS-CoV-2 infections, which in severely affected people can lead to the formation of clots.
And the lower rate of clots in J&J’s vaccine compared with Oxford–AstraZeneca’s could be because the version of spike generated by the J&J vaccine was engineered to remove the sites that allow the RNA to be processed into splice variants, says Marschalek.
One possible factor affecting the safety of adenoviral vaccines is how they are administered. The COVID-19 vaccines are given as injections into muscle, but if the needle happens to puncture a vein, the vaccine could enter the bloodstream directly. Leo Nicolai, a cardiologist at Ludwig Maximilian University of Munich, Germany, and his colleagues found in a mouse study that platelets clump together with adenovirus and become activated when the Oxford–AstraZeneca vaccine is injected into blood vessels, but not when it is injected into muscle11.
It’s possible, says Nicolai, that on rare occasions, a vaccine is inadvertently injected into a vein — as was done in the earlier mouse studies that found that adenovirus could bind to platelets. If so, many cases of VITT might be avoided by asking vaccinators to first draw a small amount of fluid from the injection site with the syringe to check for blood before they actually push the plunger to administer the vaccine. This is already standard practice in some countries, and Denmark has added it to its official guidelines for COVID-19 vaccine administration.
