[1] UCL, Inst Global Hlth, London WC1N 1EH, England
[2] Univ Birmingham, Inst Immunol & Immunotherapy, Birmingham B15 2TT, W Midlands, England
[3] Imperial Coll, MRC Ctr Global Infect Dis Anal, Sch Publ Hlth, Dept Infect Dis Epidemiol, London W2 1NY, England
[4] Univ Edinburgh, Usher Inst Populat Hlth Sci & Informat, Edinburgh, Midlothian, Scotland