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Volume 32, Number 2—February 2026

Dispatch

Avian Influenza A(H9N2) Virus Transmission across Chicken Production and Distribution Networks, Vietnam

Mathew HennesseyComments to Author , Thuy Hoang Thi, Jayna Raghwani, Younjung Kim, Hoa Thi Thanh Pham, Trang Huyen Nguyen, Hung Quoc Nguyen, Joshua G. Lynton-Jenkins, Ashley C. Banyard, Ian H. Brown, Joe James, Tom Lewis, Nicola S. Lewis, Dirk Pfeiffer, Fiona Tomley, Damer Blake, Ngoc Pham Thi, Anne Conan, Vuong Nghia Bui1, and Guillaume Fournié1
Author affiliation: Royal Veterinary College, London, UK (M. Hennessy, J. Raghwani, N.S. Lewis, D. Pfeiffer, F. Tomley, D. Blake, G. Fournié); National Institute of Veterinary Research, Hanoi, Vietnam (T.H. Thi, T.H. Nguyen, H.Q. Nguyen, N.P. Thi, V.N. Bui); University of Oxford, Oxford, UK (Y. Kim); Université de Montpellier, Montpellier, France (H.T.T. Pham, A. Conan); World Organisation for Animal Health/Food and Agriculture Organization International Reference Laboratory for Avian Influenza Animal and Plant Health Agency, Addlestone, UK (J.G. Lynton-Jenkins, A.C. Banyard, J. James, T. Lewis); Pirbright Institute, Pirbright, UK (I.H. Brown); World Health Organization Collaborating Centre for Influenza Reference and Research, London (N.S. Lewis); City University, Hong Kong, China (A. Conan); French Agricultural Research Centre for International Development, Harare, Zimbabwe (A. Conan); Université de Lyon, Marcy l’Etoile, France (G. Fournié); Université Clermont Auvergne, Saint Genes Champanelle, France (G. Fournié)

Main Article

Table

Posterior estimates and posterior predictive values of avian influenza virus A(H9N2) prevalence across chicken production and distribution networks, Bac Giang, Ha Noi, Hai Duong, and Quang Ninh Provinces, Vietnam, March 2021–March 2022*

Site No. sites No. chickens H9N2-positive chickens, no (%) H9N2 prevalence, median % (95% HDI)
Site-level Bird-level in
contaminated sites		 Overall† bird-level
Farms
 50
 750
 31 (4.1)
 0.111 (0.037–0.202)
 0.414 (0.305–0.525)
 0.045 (0.014–0.086)
Distribution facilities 52 932 168 (18.0)
Retail market 16 240 38 (15.8) 0.778 (0.559–0.967) 0.212 (0.123–0.309) 0.161 (0.088–0.244)
Wholesale market 11 210 14 (6.7) 0.481 (0.163–0.850) 0.125 (0.033–0.238) 0.057 (0.014–0.117)
Slaughter point 19 363 106 (29.2) 0.725 (0.527–0.898) 0.413 (0.308–0.515) 0.295 (0.190–0.402)
Slaughterhouse 6 119 10 (8.4) 0.233 (0.014–0.542) 0.483 (0.158–0.795) 0.103 (0.002–0.286)

*HDI, high density interval. †Estimated prevalence across both contaminated and uncontaminated sites.

Main Article

1These authors contributed equally to this article.

Page created: January 29, 2026
Page updated: February 19, 2026
Page reviewed: February 19, 2026
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