The S1 protein of SARS-CoV-2 crosses the blood–brain barrier in mice

this paper suggests that the radioIodineSpike subunt1 compound [I-S1] may cross the BBB it is also stated that degradation of the I-S1 protien occurs inside BBB within 30 minutes post injection.

the radiolable is used to quantify the presence of spike protien subunit1

this is not the full S protien peplomer, this is a spike subunit S1 , the front end of the fusionmechanism complexed with radio Iodine lable.

the nature of the S1 fusion domain suggests potential for fusion with any phospholipid bilayer.

so this work has little to do with a full Spike peplomer or a complete virus particle, the model subject is a mouse not human tissue.

this work has not a thing to do with the mRNA that is a component of the vaccine so expect to be mistaken in that regard