Will hydrogen-infused water be helpful in treating coronavirus infection, especially consequences of the inflammatory response which can become rapidly fatal? How would it compare in effectiveness to high-dose vitamin C?

This is a brilliant idea you have asked about. It is indeed a superb approach that would be equal in effectiveness to high-level vitamin C exposure. As you know, that is difficult to achieve within the cells of the body and calls for special formulations to achieve high enough blood levels and then with the tissue distribution delivering adequate concentrations to be effective as an antioxidant. Molecular hydrogen will penetrate and diffuse through the tissues quite readily and is a superb antioxidant in all respects. It is safe, it is bioavailable, it is inexpensive to produce, and can be taken in unlimited dose levels, unlike vitamin C which can produce problems especially with long-term chronic exposure. The commercial systems for producing molecular hydrogen to suffuse it in water for drinking will do an adequate job. So as long as a person is not too ill to take in fluids, this will be a superb strategy. In all likelihood, it will prevent the most serious of consequences from developing in most patients. So in most instances, people will be able to ingest regular quantities to keep up their level of antioxidant potential for it to be in a therapeutic range for the duration of an illness.