#17,702
Poultry vaccination against HPAI is neither inherently good or bad. If properly designed and managed, a well-matched, and continually updated poultry vaccine campaign should be both safe and effective.
But as always, the devil is in the details.
Until relatively recently - with the notable exceptions of China, Indonesia, Egypt, Vietnam and Hong Kong - most of the world's nations have avoided the use of poultry avian influenza vaccination in favor of the long-standing OIE recommendation to `stamp out' HPAI infections by culling infected flocks.
That policy advised that vaccines should only be used as a temporary measure, stating that: `Any vaccination campaign must include an “exit strategy” i.e. a return to classic disease control measures.'
There were some pretty good reasons behind those recommendations, not the least of which is the concern that poorly applied, or poorly matched vaccines (see Egypt: A Paltry Poultry Vaccine), could promote the emergence and spread of new subtypes or vaccine-escape variants.
A 2014 EID Journal dispatch called Subclinical Highly Pathogenic Avian Influenza Virus Infection among Vaccinated Chickens, China addressed these exact concerns (bolding mine):HPAI mass vaccination played a crucial role in HPAI control in China. However, this study demonstrated multiple disadvantages of HPAI mass vaccination, which had been suspected (13,14). For example, this study showed that H5N1 subtype HPAI virus has evolved into multiple H5N2 genotypes, which are all likely vaccine-escape variants, suggesting that this virus can easily evolve into vaccine-escape variants.
This observation suggests that HPAI mass vaccination, which is highly effective in the beginning of an outbreak, may lose its effectiveness with time unless the vaccine strains are updated. Moreover, this study showed that vaccinated chicken flocks can be infected with vaccine-escape variants without signs of illness.
Just last March, in WUR: 2 of 4 H5 Poultry Vaccines Tested Appear Effective Against H5N1, we saw a less than reassuring study out of the Netherlands that looked at 4 H5 poultry vaccines (2 currently in use, and 2 new entries) and found the two older ones were ineffective.
China's massive H5+H7 poultry vaccination program over the summer of 2017 quickly shut down their H7N9 epizootic and seasonal human epidemics (2013-2017) - arguably saved their poultry industry - and also greatly reduced the number of HPAI H5N6 infections for the next several years.None of this is to say that an effective poultry vaccine campaign can't be launched, and effectively maintained.
Given how dire the situation was with H7N9, and how close the virus appeared to sparking a human pandemic, this was a remarkable success.
When H5N1 was an infrequent visitor - as it was to Europe and the Americas until a few short years ago - stamping out of infected poultry was considered the least objectionable control option.
H5N1 was primarily a disease of poultry, and had trouble maintaining itself for very long in wild and migratory birds (see PNAS: The Enigma Of Disappearing HPAI H5 In North American Migratory Waterfowl), limiting its ability to spread.
But HPAI H5's behavior in wild birds changed markedly following a reassortment event in China/Russia in 2016 - allowing it to persist year-round, and spread efficiently via a variety of avian (and potentially terrestrial) species.
Many countries who once eschewed the use of poultry vaccines now view it as the only way to protect their poultry industry against a viral juggernaut. Last spring, in WOAH: Rethinking Avian Influenza Prevention and Control Efforts, we looked at some of the challenges of safely implementing HPAI poultry vaccination campaigns.
Since then a number of countries - including France - have announced their intention to move to poultry vaccination this fall.
This clash between vaccination policies can have a big impact on international trade, with countries that don't vaccinate unwilling to import poultry from countries that do. Literally billions of dollars are at stake.
Even though the United States is conducting HPAI poultry vaccine trials of their own, and has authorized the use of experimental H5 vaccines to protect endangered Condors, HPAI poultry vaccines are not currently approved for use in U.S. poultry.
With France about to roll out their poultry vaccination campaign, yesterday the USDA issued the following statement:
USDA Protects U.S. Poultry with Restrictions on Poultry and Poultry Products from France and the European Union
Published: Sep 29, 2023
Contact:APHISpress@usda.gov
WASHINGTON, September 29, 2023 – The U.S. Department of Agriculture's Animal and Plant Health Inspection Service (APHIS) is placing restrictions on the importation of poultry from France, as well as live ducks, duck eggs, and unmitigated/untreated duck products from the APHIS-recognized European Poultry Trade Region (EPTR, excluding Great Britain) as well as Iceland, Switzerland, Liechtenstein, and Norway. These restrictions are due to increased risk of introducing Highly Pathogenic Avian Influenza (HPAI) into the United States and will be effective October 1, 2023.
The restrictions are based on the World Organisation for Animal Health’s definition of poultry and are the result of France’s decision to vaccinate commercial meat ducks against HPAI. France’s decision to vaccinate presents a risk of introducing HPAI into the United States.
The United States does not currently allow the import of poultry from countries affected with HPAI or from flocks that have been vaccinated by HPAI. Vaccination of poultry against HPAI virus may mask HPAI virus circulating in poultry. Vaccinated birds may not show signs of HPAI infection, which could lead to the export of infected live animals or virus-contaminated products to the United States.
European Union (EU) Member States and other European countries have open access to the European common market for trade in avian commodities. Many of these countries are also part of the EPTR for export purposes. The EPTR allows listed European countries to self-impose and self-lift restrictions for HPAI disease for the purposes of trade.
When the EPTR was established, European countries were not considering vaccination against HPAI at the time. Therefore, APHIS did not evaluate HPAI vaccination in the review of the European countries. Vaccination against HPAI leaves the United States potentially exposed to an undetermined risk from EPTR imports. With the way poultry moves under the EPTR, we currently cannot be assured countries trading in the European common market can reliably certify that exports do not originate from European countries that vaccinate poultry for HPAI. Accordingly, these restrictions address the risk of open trade within Europe while accounting for the higher risk with imports from France.
APHIS is engaged in ongoing discussions with the European Commission about HPAI vaccination programs in the EU.
The caveat being that a quick or cheap fix - using poorly-matched vaccines, or applying them improperly or inconsistently - could easily make matters worse (see J. Virus Erad.: Ineffective Control Of LPAI H9N2 By Inactivated Poultry Vaccines - China).
