1 Medical Research Council Centre for Global Infectious Disease Analysis and National Institute for Health and Care Research Health Protection Research Unit in Modelling and Health Economics, Imperial College London, London W2 1PG, UK; Modelling and Economics Unit, UK Health Security Agency, London, UK. Electronic address: p.white@imperial.ac.uk.
2 Medical Research Council Centre for Global Infectious Disease Analysis and National Institute for Health and Care Research Health Protection Research Unit in Modelling and Health Economics, Imperial College London, London W2 1PG, UK.