[1] Univ Bristol, Dept Social Med, Bristol BS8 2PR, Avon, England
[2] Univ Melbourne, Murdoch Childrens Res Inst, Vaccine & Immunisat Res Grp, Melbourne, Vic 3010, Australia
[3] Univ Melbourne, Sch populat Hlth, Melbourne, Vic 3010, Australia
[4] Ctr Infect, Hlth Protect Agcy, Immunisat Dept, London, England
[5] Ctr Dis Control & Prevent, Natl Ctr Infect Dis, Div Bacterial & Mycot Dis, Atlanta, GA USA
[6] London Sch Hyg & Trop Med, Infect Dis Epidemiol Unit, London WC1, England
[7] UCL, Inst Child Hlth, Immunobiol Unit, London, England
[8] World Hlth Org, Initiat Vaccine Res, Geneva, Switzerland