The UMF of Manuka honey

Searching for some information about Manuka honey on Internet, I found some articles: "Harnessing honey's healing power"(BBC News), "Doctors turning sweet on healing with honey"(CNN News), "Honey may take the sting out of the NHS superbugs"(The Daily Mail), and "Raising spirits"(The Guardian) accidently. According to them, the exact component of the UMF is still unknown. I really wonder what the factor exactly is. (But I also wonder how long it would take to unveil the mystery...)