In February 2021, I was one of the earliest to warn the public about the mRNA COVID vaccines, and the earliest that I have seen to show the evidence of harm to multiple bodily organs, as evidenced from CDC, FDA and peer-reviewed documentation. I continued to add to that document through July 2021. The link is here: https://www.primarydoctor.org/covidvaccine
That information has not yet been refuted, only augmented by additional corroborating evidence from all over the world since its publication.
Regarding the brain, we had information from back before most Americans had taken any of the spike protein-generating COVID vaccines, that spike proteins could be a threat to the brain. Nature Neuroscience reported that the spike protein crosses the blood-brain barrier in mice.  This seems to be due to the spike protein having a pro-inflammatory effect on brain endothelial cells that in turn alters the function of the blood-brain barrier. 
Now, in a pre-print study, researchers who were working on imaging for cancer patients found unexpected effects of the Pfizer mRNA vaccine on mitochondria in the brain. They observed down-regulation of each of the following: cytochrome c, oxidative phosphorylation and ATP production. This effect is a direct threat to overall well-being and energy as well as a potential threat to immune function. All of these effects were seen in the glial cells of the brain by those researchers. 
Glial cells are crucial to brain function. They govern basic bodily functions including breathing, and they supply oxygen to neurons. They physically and nutritionally support and insulate neurons. While separating neurons, glial cells maintain the synaptic connections among neurons, and they are necessary for memory. They maintain the blood-brain barrier. It was in these crucial brain cells that the cancer imaging researchers happened to find the above changes in mitochondrial function after incubation with the Pfizer mRNA vaccine.
The late virologist Luc Montagnier, Nobel laureate in medicine, gave a speech in January 2022, shortly before he died, to the Luxembourg Parliament, in which he mentioned the prion component of the COVID vaccines.
Luc Montagnier said in his speech:
“These vaccines are poisons. They are not real vaccines. The mRNA allows its message to be transcribed throughout the body, uncontrollably. No one can say for each of us where these messages will go. This is therefore a terrible unknown. And in fact we are now learning that this is a work published over a year ago that these mRNAs contain an area that we can call prion, which is an area capable of introducing protein modifications in an unpredictable way. . . . The 3 vaccines Pfizer, AstraZeneca, Moderna contain a sequence identified by information technology as transformation into a prion. There is therefore a known risk to human health.”
Time will tell. It will tell the story of panic-based decisions to take experimental injections versus the prudence of declining to be a test subject for such experiments. It will tell the story of human rights abuses by employers and governments who forced people to take medical treatment against their will. And I hope that time will also tell a subsequent story of justice and a new pre-eminence of human rights and civil liberties.
 E Rhea, A Logsdon, et al. The S1 protein of SARS-CoV-2 crosses the blood-brain barrier in mice. Nature Neurosci. Vol 24. Mar 24 2021. 368-378. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8793077/
 T Buzhdygan, B DeOre, et al. The SARS-CoV-2 spike protein alters barrier function in 2D static and 3D microfluidic in-vitro models of the human blood-brain barrier. Neurobiol Dis. Dec 2020. 146: 105131. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7547916/
 H Abramczyk, B Brozek-Pluska, K Beton. Decoding COVID-19 mRNA vaccine immunometabolism in the central nervous system: human brain normal glial and glioma cells by Raman imaging. bioRxiv. Mar 2, 2022. https://www.biorxiv.org/content/10.1101/2022.03.02.482639v1