[1] Univ Melbourne, Sch Populat & Global Hlth, Melbourne, Vic, Australia
[2] Univ Hong Kong, Sch Publ Hlth, WHO Collaborating Ctr Infect Dis Epidemiol & Cont, Hong Kong, Peoples R China
[3] Univ Melbourne, Royal Melbourne Hosp, WHO Collaborating Ctr Reference & Res Influenza, Peter Doherty Inst Infect & Immun, Melbourne, Vic, Australia
[4] Univ Melbourne, Doherty Dept, Peter Doherty Inst Infect & Immun, Melbourne, Vic, Australia
[5] Univ Calif Los Angeles, Dept Epidemiol, Fielding Sch Publ Hlth, Los Angeles, CA USA
[6] Burnet Inst, Melbourne, Vic 3004, Australia
[7] Monash Univ, Sch Publ Hlth & Preventat Med, Melbourne, Vic 3004, Australia