[1] Univ Nottingham, Virus Res Grp, Biomed Res Unit, Nottingham NG7 2RD, England
[2] Royal Hallamshire Hosp, Sheffield Teaching Hosp Fdn Trust, Sheffield S10 2JF, S Yorkshire, England
[3] Univ Sheffield, Sch Med, Dept Infect & Immun, Sheffield, S Yorkshire, England