I don’t think the HEPA filters can filter out microbes like the Wuhan Flu, but it is a very effective filter otherwise, for pollen, smoke, etc..
The UV light, specifically Ultraviolet-C is an effective germ killer. I have one room-sized filter that has such a light in it. I have no idea how effective it is, since I can’t do an A/B comparison but all I’ve read supports this type of filter.
Unfortunately, they aren’t as cheap as HEPA filters.
Yep, those UV+C duct cleaners are -expensive-