Do UV air purifiers reduce the risk of being infected by the common cold or the flu?

Question

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.)

For example:

• US Air Purifiers

  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.

• MicroLux, via a retailer:

  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?

Answer 1

Plausible, but under-researched.

Lawrence Berkeley National Laboratory has this to say about UV germicidal irradiation (UVGI):

There have been few published studies of the health benefits of applying UVGI systems in ducts of HVAC systems outside of health care facilities. In a study within three office buildings [50], UVGI systems were turned on and off multiple times while not informing occupants. Work related self-reported acute health symptoms were assessed using questionnaires. There were statistically significant 20% to 40% decreases in symptoms during periods of UVGI system operation.

The study referenced as "[50]" is Effect of ultraviolet germicidal lights installed in office ventilation systems on workers' health and wellbeing: double-blind multiple crossover trial as published in The Lancet in 2003.

To briefly restate its conclusions (while adding my own emphasis):

On the basis of within-person estimates, use of UVGI was associated with significantly fewer work-related symptoms overall (adjusted odds ratio 0·8 [95% Cl 0·7–0·99]), as well as respiratory (0·6 [0·4–0·9]) and mucosal (0·7 [0·6–0·9]) symptoms than was non-use.

Finally, Berkeley Lab concludes:

In summary, studies of the health benefits of applying UVGI systems have inconsistent results. Also, there have been very few studies of UVGI in HVAC systems outside of health care facilities.