I think it's pretty simple, but unfortunate. HHV6 and CMV establish latent infections just like EBV and VZV. If our immune systems don't have the ability to keep the viruses latent, which it appears they don't, then the viruses will eventually reactivate and replicate to the point where they are causing significant symptoms again. Then you have to do another round of antivirals until you knock them back into latency. Round and round you go. You can't eliminate the virus, all you can do is keep knocking it back periodically.
I think you are right with this analysis, and of course the same thing occurs with interferon for enteroviruses: Dr Chia found many ME/CFS patients do get much better with a course of interferon, sometimes achieving full remission for as much as a year after taking interferon, but then ME/CFS comes back again.
Though one might have hoped that if you significantly reduce a viral infection using a course of antivirals, then the immune system might thereafter be able to keep the viral infection in check on its own, much the same as when you use antibiotics to significantly curtail a rampant bacterial infection, the immune system is thereafter able to keep the bacterial infection in check (if it couldn't, the antibiotics would be pretty useless).
Perhaps, as you suggest, it is because our immune systems don't have the ability to keep these viruses in check, so that even when the antivirals have brought the viral infections under control, these infections slowly return after you stop the antivirals.
This makes me wonder whether those who have achieved significant improvement from a course of Valcyte might benefit from thereafter taking a lower dose of Valcyte (say a quarter of their previous dose) in order to try to keep the virus at bay, and thus maintain their health gains. Using such a reduced dose will lower costs and presumably lower potential side effects. Or do doctors not recommend the indefinite use of Valcyte?
