Depends on the dose of the UV. UV is radiation. Nucleic acids (DNA & RNA) aren't stable in high UV environments. They undergo chemical changes which can make it so the enzymes that copy them either won't bind or won't correctly make copies. Radiation kills. Human cells have several DNA repair mechanisms. Viruses typically don't, so they "die".

You may also see this in hospitals. A robot will "clean" a patient room after discharge by scanning it with UV light which kills bacteria.