The article I summarize here goes over some of the specific bad vaccine reactions for SARS-1. I expect similar challenges for SARS-2.
In situations where someone took the vaccine, then gets infected by the contagion, they can have a bad reaction where the course of the disease is more severe than if they had not been vaccinated at all.*
Here's some of what we know about those bad reactions**
- Th-2 type immune activation definitely happens
- This is an allergy-like immune response
- Th-2 reactions happen in severe cases of COVID-19 generally
- There might also be a bad complement system related reaction
- Complement system means protein complexes that kill cells by poking holes in membranes
- Antibody Dependent Enhancement (ADE) might be possible, but is not likely
- This is when imperfect antibodies are used as an anchor for the virus to infect white blood cells.
- UPDATE: A related thing now strikes me as somewhat likely. It might be fusing with some white blood cells (at least T-cells) and ordering them to apoptose (activate cell-death). Article, h/t CellBioGuy.
* Going off of some other bits of research on this, these individuals probably have lower virus-titer, but higher severity and lethality. A damaging immune response, basically.
** Which vaccine types cause this bad reaction? For SARS-1, any whole-S-protein vaccines were more prone to this bad reaction. Some smaller S-protein fragments didn't have this issue, hopefully the same fix works for SARS-2. I heard of at least one case where an N-protein-only vaccine attempt also resulted in the Th-2 reaction, though. It's not totally clear how to avoid triggering it.
So maybe the speed-up you really want is to vaccinate, then deliberately expose to the live virus, and monitor what happens?
This is the type of test I'd rather we do on animal models than humans, to be frank. It seemed that you could test this phenomenon just fine with SARS-1 in animal models.