While zappers are not yet perfected, that is the one thing that I feel has the potential to stop any viral infection in its tracks or at least reduce the overall effects to a manageable level.
In general, there are certain frequencies that are better across the board, there are also certain frequencies that are better for certain specific microbes, and then, one frequency is almost never enough to do the complete job.
Multi frequency is the way to go, not only in my opinion but as a common sense guide.