Department of Epidemiology and Surveillance, National Institute for Public Health and the Environment, Bilthoven, The Netherlands.|Department of Epidemiology and Surveillance, National Institute for Public Health and the Environment, Bilthoven, The Netherlands.|Department of Infectious Disease Epidemiology, Imperial College London, London, United Kingdom.|Department of Mathematics, Imperial College London, London, United Kingdom.|Department of Epidemiology and Surveillance, National Institute for Public Health and the Environment, Bilthoven, The Netherlands.