Acknowledgements
We are grateful to the organisations that have provided funding for this special edition: Boehringer Ingelheim, Merck, HEARD, the Evidence for Action Research Programme Consortium (RPC), the Team for Applied Research Generating Effective Tools and Strategies for Communicable Disease Control (TARGETS) RPC (RPCs are funded by the UK Department for International Development), and the School of International Development, University of East Anglia, UK.