[1] Dalhousie Univ, Dept Med Geriatr, 5955 Vet Mem Lane, Halifax, NS, Canada
[2] Dalhousie Univ, Canadian Ctr Vaccinol, Halifax, NS, Canada
[3] UCL, MRC Unit Lifelong Hlth & Ageing, London, England
[4] Hlth Sci North Res Inst, Sudbury, ON, Canada
[5] Dalhousie Univ, Dept Med Infect Dis, Halifax, NS, Canada
[6] Dalhousie Univ, Dept Family Med, Halifax, NS, Canada
[7] Dalhousie, Dept Microbiol & Immunol, Halifax, NS, Canada
[8] Shantou Univ, Lab Immun, Med Coll, Shantou, Peoples R China