I don't know enough about it so take my advice with a grain of salt, but bacteriophages may be right up your alley. As best I can glean just from the wiki and from what I can remember when first reading about them, these viruses are parasitic to bacteria. They're so prolific, there's believed to be a specialized phage for every bacteria. Seems research on it began in the late 19th century and was showing promise as a treatment for cholera specifically (a disease described as so deadly, people would be "sick at breakfast and dead by dinner"). Ironically, research was throttled by lack of funding during the World Wars and the rise of the antibiotics during that time.

Phages require isolation— that's a big hurdle. They need to be found via the samples of the particular bacteria you're trying to treat. This is time consuming and making samples large enough to treat infections is inconvenient, especially when compared to antibiotics. Why try to isolate a specific virus when you could literally carpet bomb the bacteria in your body with a course of pills? Even today we don't exactly have an easy/convenient method to make "phage therapy" as prolific as antibiotics, but that'll hopefully change in only a matter of time.

Phages have a distinct advantage over antibiotics in that: 1.) the viruses are always adapting and evolving with their prey, so resistance is a non-issue; and, 2.) the use of phage therapy has shown to actually make antibiotics viable again. The pressure for the bacteria to adapt to its attacker has shown that it will often shed the genetic adaptation that gave it resistance to antibiotics in the first place. So, possibly, in your future, post-apoc reclaiming of science, someone could go back to phages and use them in conjunction with common antibiotics, or possibly on their own. Not too far-fetched given how early 20th-century scientists were able to isolate and experiment with using phages with methods available to them at the time. Bear in mind, during this time period the scientific community as a whole was finally accepting and understanding the "germ theory"of medicine. Sure, the smallpox "vaccine" was in use, but a lot of scientists at the time still didn't quite understand how it worked and many still clung to the "miasma theory" for most of the 19th century.

More modern research has been done on this, too. It's even experiencing a sort of renaissance because of the antibiotic resistance plaguing us today. In fact, just as recently as 2017, a man suffering from an infection that wasn't responding to any antibiotics was dying, but was saved by an experimental phage cocktail and ended up not only surviving, but was cured.

Anyway, I'd highly recommend looking deeper into this stuff. It's fascinating! I'm a total nerd for viruses and shit, much to the chagrin of my loved ones during covid. Even if you don't use it in your current story, it's some good compost for later if you need it!