Nature Reviews Drug Discovery 14, 167–182 (2015); doi:10.1038/nrd4529

The citation number for reference 41, a World Health Organization monthly risk asssesment summary, was missing in the article text and reference list. This has been corrected in the online version. The statement at the end of the legend for Figure 1, related to the permission to adapt a figure in reference 227, has also been modified.