[1] ROYAL FREE HOSP, ACAD UNIT TRAVEL MED & VACCINES, LONDON NW3 2QG, ENGLAND
[2] UNIV LONDON SCH MED, LONDON, ENGLAND
[3] UNIV ROSTOCK, KLIN & POLIKLIN INNERE MED, D-18057 ROSTOCK, GERMANY
[4] PASTEUR MERIEUX SERUMS & VACCINS, MARNES LA COQUETTE, FRANCE
[5] CTR HOSP A MIGNOT, SERV MED PREVENT, F-78157 LE CHESNAY, FRANCE
[6] CTR HOSP INTERCOMMUNAL, SERV MED PREVENT, F-78303 POISSY, FRANCE
[7] ROYAL FREE HOSP, SCH MED, WHO, COLLABORATING CTR RES & REFERENCE VIRAL DIS, LONDON, ENGLAND