1. From the Immunisation and Countermeasures Division (S.N.L., S.R.P., H.C., J.W., M.E., M.E.R.) and the Statistics, Modelling, and Economics Department (N.A.), Public Health England, and the Paediatric Infectious Diseases Research Group, St. George’s University of London (S.N.L.), London, and the Meningococcal Reference Unit, Public Health England, Manchester Royal Infirmary, Manchester (X.B., J.L., R.B.) — all in the United Kingdom.