For reasons that are less than clear, poultry outbreaks and human infections with avian H5N6 and H7N9 have been unusually subdued in China this winter, with just 5 human cases reported (3 H7N9, 2 H5N6) since October 1st of 2017.
By comparison, at this time last year (week 9), Mainland China had reported a record 477 human H7N9 infections.What accounts for this precipitous drop in outbreaks and human cases is a a bit of mystery.
China did undertake an emergency national poultry vaccination program last summer using - for the first time - a combination H5+H7 vaccine, and that may be greatly suppressing the virus.
But at the same time China has increased enforcement of live market closings, and sanitary regulations. Tactics that - in the past - have greatly reduced human infections from H7N9 (see The Lancet: Poultry Market Closure Effect On H7N9 Transmission).
Additionally, over the past 6 months China has unusually endured two severe seasonal flu outbreaks, an H3N2 influenza A epidemic last summer, followed by an Influenza B epidemic this winter.
As we've discussed previously (see PLoS Comp. Bio.: Spring & Early Summer Most Likely Time For A Pandemic), heavy seasonal flu activity may create temporary community immunity against other viruses, effectively blocking the spread of a novel virus.Whether due to one (or a combination) of the above reasons - or to something else entirely - after last year's record number of outbreaks, this pull back is welcome bit of relief.
How long it will last is another question entirely.All has not been completely quiet, however, with China's Ministry of Agriculture announcing yesterday an outbreak of HPAI H5N6 (presumably the Asian variety), in Guangxi Province.
An outbreak of H5N6 subtype HPAI in Lingchuan County, Guangxi Zhuang Autonomous Region
Date: 2018-03-05 16:45 Author: Source: Ministry of Agriculture Information Office
The Information Office of the Ministry of Agriculture released on March 5 a flock of H5N6 subtype HPAI in Lingchuan County, Guilin City, Guangxi Zhuang Autonomous Region.
February 22, Guangxi Zhuang Autonomous Region Guilin Lingchuan County, a breeding farm duck appeared suspected bird flu symptoms, the incidence of 28,000, 23,950 deaths. February 25, autonomous region animal disease prevention and control center diagnosed as suspected bird flu outbreak. March 5, the national bird flu reference laboratory confirmed that the outbreak was H5N6 subtype of HPAI outbreak.
After the epidemic occurred, the local government worked hard to deal with the epidemic effectively in accordance with the relevant preplan and the technical regulation on prevention and treatment, and cull and detoxify 30,462 poultry. At present, the outbreak has been effectively controlled.
Although I haven't seen an official announcement from China's MOA, the FAO is also reporting overnight an outbreak of LPAI H7N9 in Shaanxi Province, which apparently occurred in mid-February.
While last summer's introduction of a combination vaccine may very well be causing this drop in bird flu activity in China, as we've discussed previously (see MPR: Poultry AI Vaccines Are Not A `Cure-all’ & The HPAI Poultry Vaccine Dilemma), poultry AI vaccines have a poor track record of being long-term solution for avian flu.
They may suppress avian flu viruses, but they don't always eliminate it.And as avian viruses evolve, poultry vaccines become increasingly less effective; often only masking the symptoms of infection. Poor vaccine matches can then allow AI viruses to spread silently among flocks, to continue to reassort and evolve, and potentially lead to the emergence new subtypes of avian flu.
A few earlier blogs on that include:
Subclinical Highly Pathogenic Avian Influenza Virus Infection among Vaccinated Chickens, China).While one hopes the Chinese have hit a home run with their new poultry vaccine, as the headline from last August reminds us (see Vietnam: Thousands Of Vaccinated Chickens Die Of Suspected H5N1), pharmaceutical victories over rapidly evolving viruses and bacteria are often fleeting.
Study: Recombinant H5N2 Avian Influenza Virus Strains In Vaccinated Chickens
EID Journal: Subclinical HPAI In Vaccinated Poultry – China
So we'll be watching for any signs of `breakthrough' events, such as the one reported above from Vietnam, in the months ahead.