[1] London Sch Hyg & Trop Med, Med Res Council Unit Gambia, Fajara, Gambia
[2] London Sch Hyg & Trop Med, Dept Infect Dis Epidemiol, London, England
[3] Univ Liverpool Liverpool Sch Trop Med, Educ Dept, Pembroke Pl, Liverpool L3 5QA, Merseyside, England
[4] Univ Auckland, Dept Paediat, Auckland, New Zealand
[5] Minist Hlth & Social Welf, Natl Publ Hlth Lab, Kotu, Gambia
[6] Minist Hlth & Social Welf, Edward Francis Small Teaching Hosp, Banjul, Gambia
[7] Natl Inst Biol Stand & Control NIBSC, Potters Bar, Herts, England
[8] Minist Hlth & Social Welf, Directorate Hlth Serv, Banjul, Gambia
[9] Murdoch Childrens Res Inst, Melbourne, Vic, Australia
[10] Minist Hlth & Social Welf, Expanded Programme Immunizat, Kotu, Gambia
[11] WHO, Reg Off Africa, Brazzaville, Rep Congo
[12] WHO, Geneva, Switzerland
[13] Amer Red Cross, Washington, DC 20006 USA
[14] London Sch Hyg & Trop Med, MRC Trop Epidemiol Grp, London, England
[15] London Sch Hyg & Trop Med, Dept Pathogen Mol Biol, London, England
[16] Univ Warwick, Warwick Med Sch, Microbiol & Infect Unit, Coventry, W Midlands, England
[17] London Sch Hyg & Trop Med, Dept Dis Control, London, England
[18] Univ Melbourne, Dept Paediat, Melbourne, Vic, Australia
[19] Inst Rech Sante Surveillance Epidemiol & Format, Dakar, Senegal