I doubt it would help much, for similar reasons why you don't give a flu vaccine to someone already sick.
A vaccine is meant to stimulate adaptive immunity which culminates in formation of memory cells - highly selected T and B lymphocytes which are very specific to the infectious agent.
This process typically takes a couple days [1] and is rather involved. Once you have the memory cells, however, the next time you get in contact with the virus your memory cells will jump-start the immune response much more quickly, before the virus gets a chance to replicate.
In a regular infection the same mechanisms of adaptive immunity are activated, but on top of that you already have the complications from the virus itself (cell death in lung epithelium, accumulation of excess fluid, hypoxia, cytokine storm etc). A vaccine dose won't necessarily speed it up, there are plenty of virus particles already stimulating the immune system - it's just picking up the slack a bit too late.
There are other factors to consider but that's the general idea.
A vaccine is meant to stimulate adaptive immunity which culminates in formation of memory cells - highly selected T and B lymphocytes which are very specific to the infectious agent. This process typically takes a couple days [1] and is rather involved. Once you have the memory cells, however, the next time you get in contact with the virus your memory cells will jump-start the immune response much more quickly, before the virus gets a chance to replicate.
In a regular infection the same mechanisms of adaptive immunity are activated, but on top of that you already have the complications from the virus itself (cell death in lung epithelium, accumulation of excess fluid, hypoxia, cytokine storm etc). A vaccine dose won't necessarily speed it up, there are plenty of virus particles already stimulating the immune system - it's just picking up the slack a bit too late.
There are other factors to consider but that's the general idea.
[1] https://www.researchgate.net/figure/Kinetics-of-CD8-T-cell-d...