What is the mechanism of Post-acute COVID-19 Syndrome, and what percentage of cases produces such symptoms?

This is approximately 10% of cases, so it will be a serious problem and a serious burden to the healthcare system and the economy, both. It is most unfortunate but a characteristic of this virus that it has a particularly insidious effect on the immune perception of danger such that it will cause many kinds of autoimmune recognitions that are inappropriate, but leave the patient subject to a long-term and chronic immune attack that can take place within many organs in the body. Because most organs and tissues are deeply housed and insensate, except for extreme perturbations when symptoms like pain might arise or a gross derangement of physiologic function from a large degree of tissue destruction, these mechanisms can fester and persist and take a toll over time. Those involved with the nerves directly, and the brain, will be more noticeable and will be perceived as local disturbances, like headaches, muscular pains, problems with balance and coordination, weakness, and sensory abnormalities like tingling and loss of sensation, loss of touch. This is mostly a consequence of damage that commences during the acute phase of the disease. There can be a persistence of viable organisms within the body as well, and that is a second class of complications, but this will usually be presumed to be a consequence of reinfection rather than a lack of complete clearing from the prior bout of illness. This is yet another argument to maximize the use of effective anti-viral therapy, as with ivermectin and hydroxychloroquine in addition to azithromycin, because the former agents can be used for a somewhat longer course of administration to achieve the maximum clearance of viable organisms from the body. Unfortunately, this is a nuance that will take quite some time for medicine to uncover.