[1] MRC,FAJARA,SENEGAMBIA
[2] UNIV STOCKHOLM,DEPT IMMUNOL,S-10691 STOCKHOLM,SWEDEN
[3] UNIV LONDON LONDON SCH HYG & TROP MED,TROP HLTH EPIDEMIOL UNIT,LONDON WC1E 7HT,ENGLAND
[4] KABI AB,STOCKHOLM,SWEDEN
[5] ST GORANS CHILDRENS HOSP,S-11281 STOCKHOLM,SWEDEN