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Tom Peto and colleagues point out, reasonably, that the effect of mass drug administration (MDA) on malaria could be affected substantially by patterns of human movement, and that our Article1 does not consider the effects of the specific patterns of movement they observed in Cambodia and west Africa. The purpose of our Article1 was to derive general results about the possible effect of MDA and to test how robust these are to the assumptions in different models, so we avoided assumptions about population movement that are specific to any particular place. Migration is among several factors that the different groups in our collaboration have investigated as potential modifiers of the effects of mass treatment in specific situations. For those analyses, we have used field data or realistic assumptions of migration rates.2–4 Human migration is a particularly complicated modifier; the endemicity of malaria in the places from which immigrants or temporary visitors originate could be important, not just the season and extent of migration.

c situations. For those analyses, we have used field data or realistic assumptions of migration rates.2–4 Human migration is a particularly complicated modifier; the endemicity of malaria in the places from which immigrants or temporary visitors originate could be important, not just the season and extent of migration. A thorough empirical investigation of the implications of different patterns of migration for the effect of MDA would require a prohibitively complex set of field trials. Corresponding in silico analyses, parameterised with local field data, are more feasible but still represent an extensive piece of research in their own right, which is well beyond the scope of our Article.1 Some of our research groups use extensive field data collection for this exact purpose.5 The questions addressed in our Article1 were raised by WHO for their Evidence Review Group on mass treatment of malaria, which contains many experts who work directly on MDA interventions. Furthermore, several ongoing modelling exercises are being carried out by the authors of our Article1 in collaboration with control programmes to assess the potential effect of MDA in specific settings.6 We agree with Peto and colleagues on the importance of modelling groups and field researchers working closely together to better inform models and improve predictions of intervention outcomes. Involvement of modellers in trial design and operational planning for specific interventions allows questions to be framed as accurately as possible for relevant geographies and broader policy recommendations, and we hope that the number of these exercises will increase in the coming years.

ns of intervention outcomes. Involvement of modellers in trial design and operational planning for specific interventions allows questions to be framed as accurately as possible for relevant geographies and broader policy recommendations, and we hope that the number of these exercises will increase in the coming years. ACG declares grant funding from the UK Medical Research Council (MRC), Bill & Melinda Gates Foundation, the Wellcome Trust, the Medicines for Malaria Venture, and WHO. She has also received consultancy contracts in the past 3 years from the Medicines for Malaria Venture, Oxford Policy Management, and The Global Fund to Fight AIDS, Tuberculosis and Malaria. EMS and EAO are or have been employed by the Bill & Melinda Gates Foundation. LCO declares grant funding from WHO, the Bill & Melinda Gates Foundation, and Medicines for Malaria Venture, and has received consultancy contracts from Medicines for Malaria Venture and WHO. All other authors declare no competing interests.