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| Credit OIE |
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In the late spring of 2017 China's H7N9 epidemic appeared on the verge of spiraling out of control, with the emergence of a new, HPAI H7N9 strain and a new lineage ( Yangtze River Delta). The number of human infections during the winter 2016-17 (5th) wave had very nearly exceeded the number that had been reported in the previous four outbreaks combined.
During the early summer of 2017, China's MOA announced plans to test a new experimental H5+H7 poultry vaccine in two provinces (Guangdong & Guangxi). Less than a month later - fearing that time was running out - the MOA Ordered HPAI H7N9 Vaccine Deployed Nationwide by the fall.While past poultry avian flu vaccination programs have 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.
But, as we've discussed previously (see MPR: Poultry AI Vaccines Are Not A `Cure-all’ & The HPAI Poultry Vaccine Dilemma), AI vaccines don't necessarily stop viruses, sometimes they just suppress their symptoms. This allows viruses to spread subclinically in poultry - and when new variants invariably emerge (via reassortment or antigenic drift) - vaccines must be continually updated else they lose their effectiveness.
- As an example, a 2012 study (see Egypt: A Paltry Poultry Vaccine), examined the effectiveness of six commercially available H5 poultry vaccines then being used in Egypt; only one (based on a locally acquired H5N1 seed virus) actually appeared to offer protection.
- In 2018, a follow up study (see Sci. Reports: Efficacy Of AI Vaccines Against The H5N8 Virus in Egypt), indicated that very little had changed in 6 years.
While there is no doubting the tremendous success of China's emergency H5+H7 poultry vaccination program (see EID Journal Influenza H5/H7 Virus Vaccination in Poultry and Reduction of Zoonotic Infections, Guangdong Province, China, 2017–18), we've seen some signs suggesting that the threat of H7N9 (and HPAI H5N6) in China has not passed (see OFID: Avian H5, H7 & H9 Contamination Before & After China's Massive Poultry Vaccination Campaign).
Yesterday the CDC's EID Journal published an early release research dispatch, which describes the detection of a recently emerged antigenic variant of HPAI H7N9, one that is already spreading in several regions of China.
While this new HPAI hasn't (yet) sparked a resurgence in human cases, genetic analysis suggests this virus can bind to receptor cells in both birds and humans.
First, a link and some excerpts from the dispatch, and then I'll return with a postscript. Click the link to read this report in its entirety.
Volume 26, Number 2—February 2020
Research Letter
Antigenic Variant of Highly Pathogenic Avian Influenza A(H7N9) Virus, China, 2019
Wenming Jiang, Guangyu Hou, Jinping Li, Cheng Peng, Suchun Wang, Shuo Liu, Qingye Zhuang, Liping Yuan, Xiaohui Yu, Yang Li, Jingjing Wang, and Hualei Liu
Author affiliations: China Animal Health and Epidemiology Center, Qingdao, China
Abstract
In China, influenza A(H7N9) virus appeared in 2013, then mutated into a highly pathogenic virus, causing outbreaks among poultry and cases in humans. Since September 2017, extensive use of the corresponding vaccine, H7-Re1, successfully reduced virus prevalence. However, in 2019, a novel antigenic variant emerged, posing considerable economic and public health threats.
Since mid-2016, influenza A(H7N9), a highly pathogenic avian influenza (HPAI) virus, has led to ≈17 outbreaks in poultry in China (1–3). Extensive use of the corresponding vaccine, H7-Re1, substantially reduced the prevalence of H7N9 viruses (4,5). However, in early 2019, active surveillance detected the unprecedented and rapid emergence of a novel HPAI H7N9 virus antigenic variant in several regions of China.
Since 2013, a total of 1,567 cases of human infection with novel H7N9 viruses, associated with a high mortality rate, have been reported in China (6). Studies on circulating H7N9 viruses have suggested that they originated from poultry (7). However, strains isolated from birds at live bird markets displayed low pathogenicity in poultry (8). In early 2017, several outbreaks caused by HPAI H7N9 viruses in poultry were reported.
To control infection of poultry and reduce the risk for human exposure to H7N9 virus, development and national use of an inactivated vaccine, H7-Re1, with hemagglutinin (HA) and neuraminidase (NA) genes derived from A/pigeon/Shanghai/S1069/2013 (H7N9), has since September 2017 substantially decreased prevalence of H7N9 viruses among poultry and humans (5). In December 2018, on the basis of surveillance findings, the original vaccine was replaced with the H7-Re2 vaccine, with HA and NA genes derived from A/chicken/Guangdong/SD098/2017(H7N9).
In 2019, during active surveillance for avian influenza infection in China, we identified 7 strains of H7N9 viruses from 4,226 chicken swab samples. We isolated the strains by inoculating them into 10-day-old specific-pathogen–free chicken embryos and confirmed their identification via reverse-transcription PCR and sequencing.
(SNIP)
In China, vaccination plays a decisive role in the prevention and control of H7N9 virus–mediated infection. Earlier mass vaccination of poultry with H7-Re1 successfully induced a sharp decline in H7N9 infection prevalence among poultry and humans.
However, as of 2019, H7N9 variants have surfaced, posing a considerable economic and public health threat and highlighting the urgent need for new antigen-matched vaccines and more productive measures to eliminate highly pathogenic H7N9 viruses.
Dr. Jiang is a veterinary researcher at the China Animal Health and Epidemiology Center. His research interests are epidemiology and control of infectious diseases in animals.
After a welcomed two year lull in avian flu reports around the world - likely enhanced by the highly successful Chinese vaccination program - we've started to see subtle signs of increased AI activity over the past few months.
In 2019 we've seen at least two different novel H5N2 viruses emerge in Egypt, an H5N5 virus turn up (repeatedly) in Taiwan, and recently a journal article reported on a novel reassortant H7N2 virus originating from HPAI H7N9 in China.Given the limits of surveillance and reporting around the globe, it is fair to say there is likely a good deal that is going on we don't know about. While the current respite in avian flu threats may continue for some time, avian flu has not gone away, and we should be prepared for its return.
