I've seen several manufacturers make the claim that UV-C air purifiers can prevent the common cold and flu - primarily due to the destruction of viruses. (The ones that only purify air by filtering do not make this claim.)
Though it requires more specialized equipment, there are several air purifiers that can kill off viruses and lower your risk of getting a cold during cold season. These units use UV light to kill off cold viruses, rather than capturing them with a filter. Since viruses are so small, this is by far the best way for an air purifier to attack the common cold virus. [...] These air purifiers can all kill off not just the common cold, but also most other viruses. Though this doesn’t guarantee you won’t get a cold this winter, it will significantly reduce your overall chances.
Using seven types of filtration to clean the air, the MicroLux will reduce the spread of colds and the flu by eliminating airborne bacteria, viruses, germs, and mold spores.
Is there any direct evidence to support this claim? Is it simply assumed to be true since UV-C is able to destroy viruses?
This related question is about purifiers based on HEPA filters, rather than ultraviolet filters: Do household air purifiers prevent illness?