Ah, yes, I can see that now, "[m]ore narrowly targeted immune system boosting" is definitely an option. Although ... do we want everyone in the country/world taking the same "ImmuneBoost(TM)"...? (Not a particularly useful criticism, but still something to also think about.)

Especially if we can find ways sufficiently weighted towards bacteria. The major thing that saves us with them is that their significant low level differences from eukaryotic cells, e.g. those smaller and different ribosomes that provide a handy target for various antibiotic families (they're the organelles that synthesize proteins). Or their plant style cell walls.

(I stopped paying attention to the details of immune system in the late '70s when I noted how fast we were learning about it, i.e. for me it's something to learn/review "on demand", so I can't make any really specific suggestions as to what to do or judge the feasibility.)

I'm a fan of distributed separately-evolving defenses, and identical ImmuneBoost(TM) given to everyone, that has the same effects in everyone, could I suppose create susceptibility to some HIV-style pathogen that triggers and/or hijacks the specific boosted aspects of the immune system. HIV is very careful (i.e. has evolved) to stay dormant for a long time... it probably didn't start out that way, and suffered as a result. Any sort of pathogen that targets the immune system has to be similarly careful; otherwise it suffers the same fate of all extremely lethal pathogens: killing the host population faster than it can spread.

Another promising research avenue is bacteriophages. I don't know why it's being pursued more in the former Soviet Union than it is in the West. I suppose even with targeted bacteriophages there's some risk that they could mutate and start targeting beneficial bacteria, which would be a problem.

A cute CS-inspired theoretical approach would be to throw variable layers at the problem. With genetic engineering, create bacteria that function as a supplemental immune system, but in a very narrow way; the bacteria would, possibly in collaboration with the host immune system, generate specific bacteriophages for any pathogenic bacteria they come into contact with. Obviously it wouldn't work against pathogenic viruses, but other than the (perhaps impossible) difficulty of having a cell able to generate novel bacteriophages, it doesn't seem so outlandish. If we get to the point where we can write code for a wide variety of biological activity and get it translated into DNA, then such a bacteriophage-generating bacterium might be possible.

I realize there are pathologies imaginable with any possible solution. The question is how likely is it that natural or engineered pathogens will target whatever new targets are available. Bacteriophage-generating bacteria could be hijacked by viruses, mutated by gene transfer with harmful bacteria to do bad things, or even give their bacteriophage-generating properties to pathological bacteria which might then gain mutations to generate human-targeting viruses... wouldn't that be fun.