1 Emergency Preparedness, Response and Resilience, UK Health Security Agency, Porton Down, UK; Joint Modelling Team (JMT), UK Health Security Agency, UK.
2 Immunisation Division, UK Health Security Agency, 61 Colindale Avenue, London, NW9 5EQ, UK.
4 Department of Pediatrics, Division of Infectious Diseases and Immunology, Cedars-Sinai Medical Center, Los Angeles, California, USA.
5 NHS England and NHS Improvement, London, England.
6 NHS England and NHS Improvement, London, England; Institute of Systems, Molecular and Integrative Biology, University of Liverpool, Liverpool, UK; Department of Paediatric Surgery, Alder Hey in the Park, Liverpool, UK.
7 Immunisation Division, UK Health Security Agency, 61 Colindale Avenue, London, NW9 5EQ, UK; Paediatric Infectious Diseases Research Group, St George's University of London, UK. Electronic address: shamez.ladhani@ukhsa.gov.uk.