[1] Hlth Protect Agcy, Immunisat Hepatitis & Blood Safety Dept, Ctr Infect, London, England
[2] Hlth Protect Agcy, Stat Unit, Ctr Infect, London, England
[3] Hlth Protect Agcy, Virus Reference Dept, Ctr Infect, Resp Virus Unit, London, England
[4] Manchester Royal Infirm, Hlth Protect Agcy, Vaccine Evaluat Seroepidemiol Unit, Manchester M13 9WL, Lancs, England