The actual paper contains much more information than this BBC article. I'm not sure why they didn't link to it, but here is the original paper at the Lancet [1] as well as the full-text pdf file [2].

[1]: http://www.thelancet.com/journals/langlo/article/PIIS2214-10...

[2]: http://www.thelancet.com/pdfs/journals/langlo/PIIS2214-109X(...