CoVs lacking E make promising vaccine candidates., page-18

mxdbg

this part of the research you have quoted is worth elaborating on a little:

"During the replication cycle, E is abundantly expressed inside the infected cell, but only a small portion is incorporated into the virion envelope [65]. The majority of the protein is localised at the site of intracellular trafficking...where it participates in CoV assembly and budding"

Part of Intracellular trafficking is ion channeling, the function of the E protein that enables passing of virus particles into the host. It is this function that Biotron's compounds have been shown to inhibit.

The fact that E is well expressed in C-19 patients, as Fielding and Schoeman refer to, make it also a vaccine target, as opposed to the majority of vaccine development that utilizes S. A vaccine based on E would likely be one where E is attenuated, resulting in a harmless virus (vaccine) that would enable humans to build immunity against. Alternatively, (part of) E is mixed into a vaccine base fluid so that our immune system becomes familiar with it.

In Biotron's case, the antiviral would prevent E from doing what it does in viral replication. I believe an E vaccine would be much further away from development than a potential antiviral.