This article provides a good description of how the Pfizer vaccine works: Reverse Engineering the source code of the BioNTech/Pfizer SARS-CoV-2 Vaccine. Piece is detailed but very clear. Gist is “gee whiz” and positive for getting vacs.
This comment expresses doubt about what crosses the blood-brain barrier and potential harm from that:
Thanks for apprising me of that paper. It helps to illuminate and builds upon many of the concerns I’ve been hearing among colleagues about potential tissue trafficking and localization. If indeed the spike protein components (as translated from the transduced vaccine mRNA) are expressed at high enough levels, this seems to raise additional questions about the potential for the gene product to cross the blood-brain barrier through adsorptive transcytosis even if expressed outside of it.link to full comment
UPDATE: Here are some very important pieces of information. This comment describes what could happen if mRNA crosses the blood-brain barrier.
I think Chemist’s point is that the lipid nanoparticles may have too broad a tropism, far broader even than attenuated virus vaccines (which are still limited to the tropism of the wild-type virus), and thus could pose a uniquely high safety hazard due to cytotoxic attack on the broad cellular range that uptakes the LNPs. Since the LNPs would enter cells via endocytosis, the SARS-CoV-2 epitopes would be expressed on MHC-1 molecules, making them targets of cytotoxic CD8 lymphocytes, attacking a much greater range of cells than any previous vaccine modality. This is concerning in general, but it’s a nightmare scenario if the vaccines are crossing the blood-brain barrier and endocytosing into e.g. oligodendrocytes (multiple sclerosis risk) or motor neurons (which could possibly cause an ALS-type picture). No other vaccine has this broad tropism. That is THE major safety concern here — been working on submitting a comprehensive question to Derek about this very topic. link
And this comment claims that mRNA does cross the blood-brain barrier.
Since this article was posted, the European Medicines Agency Assesment Reports for the Moderna and Pfizer vaccines have been published, which both find some biodistribution, including across the blood/brain barrier.
The Moderna study used an intramuscular injection of the same LNP as the vaccine (but a different mRNA), and found that “low levels of mRNA could be detected in all examined tissues except the kidney [, which] included heart, lung, testis and also brain tissues, indicating that the mRNA/LNP platform crossed the blood/brain barrier, although to very low levels (2-4% of the plasma level)”, with rapid clearing from most tissues.
I think the Pfizer results are consistent with that: with radiolabelled LNP they found that “distribution from the [IM] injection site to most tissues occurred”, but again disproportionately more to the liver.
Full details can easily be found at the European Medicines Agency. link
This is just basic information we all need to understand what is happening and how we will react to it. ABN