Sawyer still has the Point ZeroTWO filter, but does not claim that it removes viruses. The specs page just says protozoa and bacteria. The RapidPure filters appear not to be simply particulate filters, but seem to incorporate some kind of electrochemical treatment. The RapidPure particulate claim is 0.2 microns, same as most everybody else. I don't generally see the need of going to greater lengths to purify backcountry water, as long as the source appears to be relatively clean. I think that the protozoans are the backcountry traveler's biggest concern, other than chemically contaminated water.

I was looking at some of the water treatment chemicals that I have and I noticed a statement on one of the chlorine dioxide (might have been Potable Aqua)packages, that the 4 hour time was for the "Chlorine Dioxide to develop". This may mean that the chemical in the tablets does not immediately react and produce chlorine dioxide. I'm not that familiar with this process, but I know that the contact time in most water treatment plants is much less than 4 hours, usually less than 30 minutes. Of course, the residence time of the water in the system before use is usually considerably longer.

I think that cross contamination and personal hygiene are far more important to the backcountry traveler then absolute purity.