Friday, October 26, 2018

EID Journal: China's H5+H7 Poultry Vaccination Program, Guangdong 2017-18


In the summer of 2017, in the wake of a disastrous spring surge in H7N9 infections and the emergence of an HPAI strain, China's MOA announced plans to test a new experimental H5+H7 poultry vaccine in two provinces (Guangdong & Guangxi).
With mounting fears that H7N9 was creeping ever closer to becoming a pandemic strain, less than a month later the MOA Ordered HPAI H7N9 Vaccine Deployed Nationwide by the fall. 
Although previous poultry vaccination programs had yielded varying levels of success, China's dramatic drop in human infections, outbreaks in poultry, and virus detection from routine surveillance has been nothing short of remarkable.
While there are always concerns that the H5 and H7 viruses targeted by this vaccine could evolve antigenically enough to evade its effects - or that other subtypes could emerge to fill the vacuum - it's hard to argue with its initial success. 
We've a dispatch, posted yesterday in the EID Journal, that looks at the dramatic impact this vaccination campaign had in Guangdong Province.  I've only included some excerpts, so follow the link to read it in its entirety.

Volume 25, Number 1—January 2019
Influenza H5/H7 Virus Vaccination in Poultry and Reduction of Zoonotic Infections, Guangdong Province, China, 2017–18

Jie Wu1, Changwen Ke1, Eric H.Y. Lau, Yingchao Song, Kit Ling Cheng, Lirong Zou, Min Kang, Tie Song2 , Malik Peiris, and Hui-Ling Yen2


We compared the detection frequency of avian influenza H7 subtypes at live poultry markets in Guangdong Province, China, before and after the introduction of a bivalent H5/H7 vaccine in poultry. The vaccine was associated with a 92% reduction in H7 positivity rates among poultry and a 98% reduction in human H7N9 cases.

Human infections with avian influenza A(H7N9) virus have been documented in China since 2013 (1). Among 1,220 confirmed H7N9 case-patients during 2013–2017, a total of 73% reported poultry exposure, and 57% had visited live poultry markets (LPMs) before symptom onset (2). Because of the lack of apparent clinical signs in poultry infected with low pathogenicity H7N9 influenza virus, it has been challenging to rapidly identify and remove infected poultry at the LPMs or farms and to justify implementation of mandatory vaccination of poultry against this virus. Interventions such as market closure during human epidemics have temporarily reduced human exposure to live poultry and decreased zoonotic infection risk (3). However, the effect was not sustainable because H7N9 viruses continue to circulate within the LPM supply chain, leading to recurrent waves of human infections in winter months (4).

During winter 2016–17, the H7N9 virus evolved into highly pathogenic avian influenza (HPAI) virus by acquiring a polybasic amino acid motif at the hemagglutinin cleavage site, rendering the virus capable of disseminating systematically and causing high mortality rates among chickens (5,6). In response to the emergence of HPAI H7N9 virus, the government of China amended the mandatory vaccination regimen for avian influenza in summer 2017.
Specifically, a newly developed bivalent H5 (Re-8, based on clade H5N1 virus A/chicken/Guizhou/4/2013) and H7 (Re-1, based on H7N9 virus A/pigeon/Shanghai/S1069/2013) vaccine replaced the previous bivalent H5 vaccine that targeted H5 clades (Re-8) and (Re-6, based on H5N1 virus A/duck/Guangdong/S1322/2010). The new bivalent H5/H7 vaccine was first introduced in Guangdong and Guangxi Provinces in July 2017; other provinces adopted the poultry vaccine by winter 2017–18.
The vaccine coverage rate reported in November 2017 in Guangdong was 97.9% (282 million birds) among the target poultry population (7), which encompassed chickens, ducks, geese, quail, pigeons, and rare birds in captivity (8); however, the reported vaccine coverage varied in different provinces (8). Layers and breeders received 2 doses of the H5/H7 vaccine, whereas broilers sold within 70 days received 1 dose (8).

To assess the effect of poultry vaccination on H7N9 prevalence in poultry and the subsequent effect on human zoonotic infection risk, we analyzed the temporal distribution of monthly H7N9 detection rates at LPMs and of human H7N9 cases in Guangdong Province during 2013–2018. We estimated the effect of the bivalent H5/H7 vaccine using a Poisson regression model.


Emergence of H7N9 highly pathogenic avian influenza virus during the fifth epidemic wave during winter 2016–17 has prompted the mandatory use of a bivalent H5/ H7 inactivated influenza vaccine in domestic poultry in China. Before then, a bivalent H5 poultry vaccine was used. Our results provided quantitative confirmation for the significant impact of the vaccine in reducing H7 detection frequency at LPMs and the corresponding reduction in human H7N9 infections in Guangdong Province, 1 year after implementation of the vaccine.
The focus should be on achieving a high vaccine coverage rate in domestic poultry in which the H7N9 virus has been detected, recognizing that antigenic drift variants that escape vaccine-induced immunity may emerge. A second concern is whether H7N9, which predominantly infected chickens, may adapt to aquatic poultry, such as ducks. Such an event would prove a major challenge for the control strategy.

In conclusion, our analyses of longitudinal surveillance data support the association between the introduction of the bivalent H5/H7 vaccine for poultry and the reduction in zoonotic H7N9 disease. These results illustrate an example of combatting zoonotic avian influenza virus at its source in a One Health approach.

Dr. Wu is the deputy chief technician for the Institute of Pathogenic Microbes at Guangdong Provincial Center for Disease Control and Prevention. Her research interest is monitoring human infection risk by avian influenza viruses at the human-poultry interface. Dr. Ke is the chief technician for the Institute of Pathogenic Microbes at Guangdong Provincial Center for Disease Control and Prevention. His research interest is pathogenic mechanisms of emerging pathogens.