While H5 poultry vaccines don't always prevent chickens and ducks from catching and spreading avian flu viruses - they generally do a good job keeping poultry from falling ill, or dying (see EID Journal: Subclinical HPAI In Vaccinated Poultry – China).
For some countries (notably China, Egypt, Vietnam & Indonesia), that offered enough of an economic incentive to make vaccination attractive, while most of the rest of the world embraced strict quarantine and culling.As we’ve discussed before (see MPR: Poultry AI Vaccines Are Not A `Cure-all’ & The HPAI Poultry Vaccine Dilemma), despite more than a dozen years of of heavy use, poultry AI vaccines have proven to be less than a panacea for bird flu. But for those countries where the virus has now become endemic, few other options remain.
The problem is that as avian viruses evolve - and diversify into multiple subtypes and lineages such as we've seen in China with H5N8, H5N6, and H7N9 - poultry vaccines must be constantly updated, otherwise they grow increasingly ineffective.
A 2012 study (see Egypt: A Paltry Poultry Vaccine), examined the six commercially available H5 poultry vaccines commonly used in Egypt; only one (based on a locally acquired H5N1 seed virus) actually appeared to offer protection.In the spring of 2010 Vietnam began reporting a number of `vaccine failures', where vaccinated poultry succumbed to H5N1. In late May Vietnam announced a cessation of poultry vaccinations until a new formulation could be developed (see Reuters Vietnam halts bird flu vaccination due to new type).
This vaccine evading virus was eventually classified as an emerging clade 22.214.171.124, which led to the following 2011 statement FAO Warns On Bird Flu.Since then it, (and its variants - primarily clade 126.96.36.199a and clade 188.8.131.52c) have become the most widely distributed versions of H5N1 on the planet, finally arriving in West Africa in late 2013.
We saw similar reports of vaccinated poultry dying in large quantities in Egypt in late 2014 (see Egypt H5N1: Poultry Losses Climbing, Prices Up 25%), followed a few months later by the the announcement in Eurosurveillance: Emergence Of A Novel Cluster of H5N1 Clade 184.108.40.206.
Although an effective vaccine doesn't necessarily prevent all morbidity in poultry, when vaccinated poultry begin dying en masse, it is sometimes a sign of an antigenic change in the virus.While there are a number of other plausible reasons why a vaccinated flock might suddenly die off in Vietnam (including poison, contaminated feed, a bad batch of vaccine, or another disease entirely), today's report is something we'll need to keep an eye on.
Chicken vaccinated is still dying of disease in Bac Lieu
Tuoi Tre Newspaper
2 hours ago
Thousands of chickens, despite being fully vaccinated, suddenly died of H5N1, while at the same time dozens of pigs died from foot and mouth disease.
On 25-8, Bac Lieu Provincial Department of Animal Health and Animal Health said that many days in Ninh Quoi A Commune, Hong Dan District, there has been a number of livestock and poultry died in numbers. big.
At three households in this locality, herds of cattle and poultry have the manifestation of H5N1 avian influenza and foot and mouth disease.
It is noteworthy that the household C.B.D in Ninh Loi hamlet raising about 3,200 chickens and according to him was fully vaccinated. About three weeks ago, Mr. D.'s chick showed signs of death.
Bac Lieu Provincial Department of Animal Health and Veterinary has sampled samples submitted and tested positive for H5N1.
The authorities have made a record to destroy the number of live birds (nearly 1,900) of his household D.
Mr. N.V.B, in Ninh Phuoc hamlet raising more than 7,000 chickens, is in the period from 2 ½ months to more than 5 months but died about 2,500.
Over 7 days of localized surveillance, the authorities found no transmission from Mr B.'s chickens to other areas, and the remaining chickens gradually developed steadily.
Meanwhile, the household Mr V.C.L in Ninh Thanh hamlet 68 pigs, but 56 died with clinical symptoms of foot and mouth disease.
Functional agencies have also sprayed disinfectants, poisonous disease zones, concentrated in all hamlets and adjacent communes such as Ninh Hoa commune, Ninh Quoi commune to avoid spreading to large areas.