title: Turnover of Village Chickens Undermines Vaccine Coverage to Control HPAI H5N1.
abstract: Highly pathogenic avian influenza (HPAI) subtype H5N1 remains an enzootic disease of village chickens in Indonesia, posing ongoing risk at the animal-human interface. Previous modelling showed that the fast natural turnover of chicken populations might undermine herd immunity after vaccination, although actual details of how this effect applies to Indonesia's village chicken population have not been determined. We explored the turnover effect in Indonesia's scavenging and mixed populations of village chickens using an extended Leslie matrix model parameterized with data collected from village chicken flocks in Java region, Indonesia. Population dynamics were simulated for 208 weeks; the turnover effect was simulated for 16 weeks after vaccination in two 'best case' scenarios, where the whole population (scenario 1), or birds aged over 14 days (scenario 2), were vaccinated. We found that the scavenging and mixed populations have different productive traits. When steady-state dynamics are reached, both populations are dominated by females (54.5%), and 'growers' and 'chicks' represent the most abundant age stages with 39% and 38% in the scavenging, and 60% and 25% in the mixed population, respectively. Simulations showed that the population turnover might reduce the herd immunity below the critical threshold that prevents the re-emergence of HPAI H5N1 4-8 weeks (scavenging) and 6-9 weeks (mixed population) after vaccination in scenario 1, and 2-6 weeks (scavenging) and 4-7 weeks (mixed population) after vaccination in scenario 2. In conclusion, we found that Indonesia's village chicken population does not have a unique underlying population dynamic and therefore, different turnover effects on herd immunity may be expected after vaccination; nonetheless, our simulations carried out in best case scenarios highlight the limitations of current vaccine technologies to control HPAI H5N1. This suggests that the improvements and complementary strategies are necessary and must be explored.
authors.affiliation: Centre for Epidemiology and Biostatistics, Melbourne School of Population and Global Health, University of Melbourne, Melbourne, Vic., Australia.|Australian Animal Health Laboratory, CSIRO, Geelong, Vic., Australia.
authors.forename: J P
authors.initials: JP
authors.lastname: Villanueva-Cabezas
authors.affiliation: Centre for Epidemiology and Biostatistics, Melbourne School of Population and Global Health, University of Melbourne, Melbourne, Vic., Australia.|Modelling and Simulation Research Group, Murdoch Childrens Research Institute, Royal Children's Hospital, Parkville, Vic., Australia.
authors.forename: P T
authors.initials: PT
authors.lastname: Campbell
authors.affiliation: Centre for Epidemiology and Biostatistics, Melbourne School of Population and Global Health, University of Melbourne, Melbourne, Vic., Australia.|Modelling and Simulation Research Group, Murdoch Childrens Research Institute, Royal Children's Hospital, Parkville, Vic., Australia.|School of Mathematics and Statistics, The University of Melbourne, Melbourne, Vic., Australia.
authors.forename: J M
authors.initials: JM
authors.lastname: McCaw
authors.affiliation: Australian Animal Health Laboratory, CSIRO, Geelong, Vic., Australia.
authors.forename: P A
authors.identifier: 0000-0003-0851-5300
authors.initials: PA
authors.lastname: Durr
authors.affiliation: Centre for Epidemiology and Biostatistics, Melbourne School of Population and Global Health, University of Melbourne, Melbourne, Vic., Australia.|Modelling and Simulation Research Group, Murdoch Childrens Research Institute, Royal Children's Hospital, Parkville, Vic., Australia.
authors.forename: J
authors.initials: J
authors.lastname: McVernon
mesh_terms: D000822:Animal Husbandry; D000818:Animals; D002645:Chickens; D003198:Computer Simulation; D005260:Female; D006801:Humans; D007214:Indonesia / Q000453:epidemiology; D053124:Influenza A Virus, H5N1 Subtype / Q000472:pathogenicity*; D007252:Influenza Vaccines / Q000276:immunology*; D005585:Influenza in Birds / Q000453:epidemiology / Q000517:prevention & control* / Q000821:virology; D008297:Male; D008954:Models, Biological; D011157:Population Dynamics; D014611:Vaccination
chemical_list: D007252:Influenza Vaccines
keywords: Avian influenza; mathematical modelling; population dynamics; poultry