I don’t understand this:
Making a pathogen that binds to exactly that “spike protein,” then uses that “spike protein” to enter a cell is now pretty trivial. Such a pathogen would only infect people with the pre-existing “spike protein.” Would be a hell of a magic bullet.
The “spike protien” (actually, it’s three protiens twisted together, but whatever) like all linear objects, has a “cis” (near) end and a “trans” (far) end.
In a natural virus, the cis end is buried in the viral envelope, with the trans end sticking out. The trans end comes across something (a vunerable cell portion) on the host to which it can stick, it (the trans end) then sticks to that thing. In nature, the covid spike protien then folds, moving the virus body towards the soon to be infected cell, priming the virus to inject its nucleic acid into the cell.
The synthetic spike proteins are almost the same. They have apparently been engineered to not fold, and their cis end isn’t already in a virus. Both of those differences can be worked around. All you need is a virus with a specific receptor for some part ... any part except the trans end ... of the “spike protein,” and no receptors for mammalian tissue. Now you’ve got a virus that can’t directly infect a mamalian cell. This has already been demonstrated with rabies virus.
Introduce pre-existing “spike proteins” and now you have a situation in which the virus sticks to some part of the pre-existing spike protein, and the trans end of that pre-existing spike protein then sticks to a mammalian cell, thus anchoring the virus to the cell. From the virus’ point of view, this is a bit more kludgy than just carrying around its own spike protien which can directly attach to a mammalian cell. The requirement that the host provide the spike protien in order to enable the virus to infect the cell means that a virus can be engineered to infect only those with specific pre existing spike proteins.
That’s the “magic” part of the “magic bullet.” Spreading horrible diseases is pretty simple, but runs the risk of infecting you and your allies. Spreading horrible diseases that only affect people who have been biochemically primed to be infected ... now THAT has military potential.