Competing interests: HN reports grants from the Health Foundation, the National Institute for Health and Care Research, UK Research and Innovation, and the Commonwealth Fund outside the submitted work, and consulting fees from the World Health Organization and Pharmaceutical Group of the European Union; HN also reports being an adviser to the Analysis section The BMJ. JC is employed by Transparency International UK, which receives unrestricted funding from GSK. AG reports consulting fees from the World Bank. IP has no competing interests to declare.