It is becoming increasingly evident that the U.S. poultry industry is divided on the desirability of preventive vaccination against Highly Pathogenic Avian Influenza. Given the duration and severity of the H5N1 epornitic that has persisted in seasonal waves of incidence since 2022, both turkey and egg production segments have been disproportionately affected.  In contrast there have been limited losses among broiler breeder and growing farms. The ongoing epornitic has resulted in depopulation of close to 90 million birds with 75 percent comprising commercial egg laying flocks or pullets, 16 percent turkeys and 7 percent broilers and broiler breeders.

At issue is the potential impact of even limited regional and sector vaccination on the export of broiler leg quarters.  The prevailing perception is that introducing any program of preventive vaccination would be an acknowledgement that the infection is endemic resulting in a number of importing nations imposing wide restrictions on importation.  The reality is that HPAI is effectively regionally and seasonally endemic in the U.S. given that both migratory birds that introduce infection and now many domestic species both serve as reservoirs and disseminators of the virus. Even the most extreme levels of biosecurity are ineffective in preventing introduction of infection based on anecdotal and scientific evidence that infection can be transmitted over short distances by the aerogenous route.  Since the 2022 epornitic, the USDA-APHIS has followed an outdated and anachronistic policy of eradication.  This is clearly a fallacious approach, inappropriate to a disease subject to seasonal introduction and with domestic wildlife reservoirs.

Adaptation of H5N1 to mammals with animal-to-animal transmission is evidenced by outbreaks in farmed mink and marine mammals during 2023.  The recognition that the infection is now present in the U.S. dairy industry raises concern for further changes in the H5N1 genome with the potential for the emergence of a zoonotic strain.

Given that highly pathogenic avian influenza caused by H5N1 is now a panornitic present on six continents, has changed attitudes towards preventive vaccination. The World Organization of Animal Health (WOAH) has accepted this modality as an adjunct to prevention along with biosecurity and quarantine.  The important question is whether limited vaccination in the U.S. would seriously impact export of leg quarters representing 97 percent of broiler exports.  Given the limited number of nations receiving U.S. exports, and the fact that many of these nations have endemic infection suggests that the restraints on exports may be overstated. It is clear that many nations have and will continue to use avian influenza as either a protective measure for domestic industries or for political purposes.  China applies vaccination against endemic HPAI but imposes prolonged restrictions on U.S. counties and states with diagnosed infections. This nation will act in their own interest irrespective of international agreements or scientific reality.  Many importing nations would be willing to limit restrictions to the county level.  Others might accept a certification program by which complexes or flocks of origin could be demonstrated to be free of virus by PCR assay prior to harvesting.

The NCC is justified in continuing to quantify the effect of trade restrictions although in reality vaccination would result in probably less disruption than is currently imposed.  The contention that vaccination would not eradicate HPAI is well recognized, but it must be accepted that the infection is now regionally and seasonally endemic.  The statement that vaccination “masks the presence of HPAI” is valid but flocks can be certified free of infection using PCR technology.

The NCC statement that “We currently support USDA and APHIS stamping out policy to eradicate the virus is essentially fallacious and self-serving since this is an unachievable objective and reflects the thinking of the 1990s.  The NCC encouragement of APHIS to “work with our trading partners to ensure that should a vaccination strategy be developed, we can continue to feed the world with poultry products” represents a departure from the ‘no-vaccination ever’ message.  The NCC is justified in its reservations over HPAI vaccination with respect to export and trade since this is of vital economic importance to the industry that must market 15 percent of RTC volume in the form of leg quarters, an undifferentiated relatively low-priced commodity.

The recent article by Mike Brown, President of the NCC, in a Delmarva publication indicates a more reasoned approach to vaccination that recognizes that the infection cannot be eradicated through ongoing depopulation of flocks.  Effective biosecurity (as opposed to the ‘make-belief’ version practiced) will not provide absolute protection against infection given the reality of aerogenous transmission.

Restriction on trade in poultry products as the result of vaccination may be influenced by future events including: -

• The unfortunate but likely possibility of introduction of HPAI into the U.S. broiler industry, resulting in significant losses.
• Recognition of HPAI among commercial flocks in Brazil.
• Extension of H5N1 or other strains to workers on U.S. livestock farms, processing and packing plants and their contacts.
• Availability of effective AI vaccines for mass application.

The “softening” of resistance by the broiler industry to preventive vaccination is encouraged and reflects an appreciation of the realities of the disease, the widespread distribution, financial impact and zoonotic potential. The NCC and USAPEEC should motivate the lifting of trade barriers against vaccination through representations to the WOAH, the International Poultry Council and the International Egg Commission to facilitate controlled and monitored immunization of egg-production and turkey flocks in U.S. areas of high risk.