Epidemiol. Infect., Page 1 of 6. © Cambridge University Press 2015 doi:10.1017/S0950268815000187

SHORT REPORT Population susceptibility to a variant swine-origin influenza virus A(H3N2) in Vietnam, 2011–2012

L. N. M. HOA 1 , J. E. BRYANT 1 , 2 *, M. CHOISY 1 , 3 , L. A. NGUYET 1 , N. T. BAO 1 , N. H. TRANG 1 , N. T. K. CHUC 4 , T. K. TOAN 4 , T. SAITO 5 , N. TAKEMAE 5 , P. HORBY 1 , 2 , H. WERTHEIM 1 , 2 A N D A. FOX 1 , 6 1

Oxford University Clinical Research Unit and Wellcome Trust Major Overseas Programme, Vietnam Nuffield Department of Medicine, Oxford University, Oxford, UK 3 MIVEGEC (UMR Universités Montpellier 1 & 2, CNRS 5290, IRD 224), Montpellier, France 4 Hanoi Medical University, Hanoi, Vietnam 5 Influenza and Prion Diseases Research Center, National Institute of Animal Health, National Agriculture and Food Research Organization (NARO), Ibaraki, Japan 6 The University of Melbourne, Peter Doherty Institute for Infection and Immunity, Department of Microbiology and Immunology, Parkville, Victoria, Australia 2

Received 15 August 2014; Final revision 16 January 2015; Accepted 21 January 2015

SUMMARY A reassortant swine-origin A(H3N2) virus (A/swine/BinhDuong/03-9/2010) was detected through swine surveillance programmes in southern Vietnam in 2010. This virus contains haemagglutinin and neuraminidase genes from a human A(H3N2) virus circulating around 2004–2006, and the internal genes from triple-reassortant swine influenza A viruses (IAVs). To assess population susceptibility to this virus we measured haemagglutination inhibiting (HI) titres to A/swine/ BinhDuong/03-9/2010 and to seasonal A/Perth/16/2009 for 947 sera collected from urban and rural Vietnamese people during 2011–2012. Seroprevalence (HI 5 40) was high and similar for both viruses, with 62·6% [95% confidence interval (CI) 59·4–65·7] against A/Perth/16/2009 and 54·6% (95% CI 51·4–57·8%) against A/swine/BinhDuong/03-9/2010, and no significant differences between urban and rural participants. Children aged