I’ve mentioned this in the past:
Since my teens (and probably earlier) I had chronic Hepatitis B.
The Hepatitis B virus expresses two antigens - a surface antigen, and a core antigen. Most people develop an immunological response to both the surface and the core antigen, and get over Hepatitis B.
About 10% of the population, and a much higher proportion of newborn infants, only develop an immunological response to the surface antigen - they never clear the disease, but also don’t really get sick. Without antibodies to the core antigen, the virus just makes the sufferers liver a battleground, and eventually cirrhosis develops (and possibly hepatic cancer). Lifestyle factors (drinking, exposure to some food toxins such as nut-borne aflatoxins) make this outcome much more likely.
Modern antivirals (similar to and in some cases the same as HIV antivirals) can be used to control the Hep-B virus, and I was on antivirals for several years with basically zero viral load. But I was on the antivirals for life. This wasn’t a problem, as the antivirals are generally well tolerated, and I lived in places with a public health system that meant there was no cost to me for the drugs.
A few years back I took part in a trial - a vaccine-based approach that used a genetically modified yeast extract that expressed the Hep-B core antigen. The hope was that this would prompt the immune system into expressing core antibodies so the virus would clear. That trial had no major effect, but obviously did have an impact on the immune system, because they persisted with a new trial.
A year later, I was invited to join this new trial, where the same antigen extract was used combined with an immune system modulator (a PCD-1 modulator used for some cancer treatments) to extend the period of immune system activity. PCD-1 modulators (where PCD means Programmed Cell Death) prevent the automatic death of immune system cells, extending their period of activity and the number of active immune cells in the system.
I was given the trial drugs, and after two weeks was called by the co-ordinator to say my liver function markers were very high, and they were concerned that I might be having an autoimmune response to the PCD-1 modulator. I had to cancel a trip to the US at short notice, and had lots more monitoring until my liver function results were back to normal.
What was actually happening was the combination of the vaccine and the PCD-1 modulator had temporarily supercharged my immune system, and I had developed those Hep-B core antibodies I had been missing for 30+ years. Six months later I stopped taking antivirals, and stopped monitoring a few months after that.
Sadly, I was the only patient in the trial to respond in that way, but research is continuing.
So vaccine-based approaches can be used to actually treat the disease - particularly if the vaccine can be used to activate the immune system while a disease is in a low activity or latent phase (as with rabies).