#18,450
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):
None of this is to suggest that an effective poultry vaccine campaign can't be mounted, or effectively maintained. But it does require more than just a `vaccinate & forget' strategy.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.
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.Given how dire the situation was with H7N9, and how close the virus appeared to sparking a human pandemic, this was a remarkable success. But over time, we've seen a rise in human H5N6 infections, which may also be spreading asymptomatically in poultry.
Since 2021, in response to the abrupt rise in HPAI H5 around the globe, more countries have elected to embrace poultry vaccination, including France and Mexico (see Senasica Orders Strategic Vaccination Of High-Risk Poultry Against HPAI H5N1).
In 2023 WOAH (formerly the OIE) announced a policy shift (see WOAH: Rethinking Avian Influenza Prevention and Control Efforts) that recommended a comprehensive control strategy that integrates vaccination with other measures (including testing & culling if needed).
But most countries - including the United States, Canada and the UK - have yet to authorize HPAI poultry vaccines, although many are studying the matter.
This statement from Canada's CFIA:
Why Canada doesn’t currently vaccinate poultry against HPAI
Canada has historically maintained an HPAI response strategy focused on disease eradication and does not currently vaccinate poultry to protect against HPAI. The scale and duration of the ongoing outbreak, however, has increased global interest in exploring vaccination as a tool for disease management. Some countries already use vaccines as a preventative measure.
Last March's UK Joint Taskforce Policy Paper: Vaccination of Birds Against HPAIV (bird flu) continues to promote eradication, warning:
Use of avian influenza vaccine may reduce poultry mortality and clinical signs of the disease following infection. However, vaccinated birds can still become infected, shed virus, and transmit the virus to other vaccinated or unvaccinated birds, mammals and humans.
There were media reports in June that the USDA was expected to announce their poultry vaccination strategy against H5N1 sometime in July, but as of today's writing no decision has been announced.
Using mis-matched vaccines, or skimping on post-vaccination surveillance and testing, could lead to escape variants that might make matters considerably worse (see Preprint: Association of Poultry Vaccination with the Interspecies Transmission and Molecular Evolution of H5 Subtype Avian Influenza Virus).While vaccinating poultry (and potentially cattle) against HPAI H5N1 could potentially be a game changer, getting it right is imperative.
We've a report today in Vaccine: X which looks at the result of two rounds of HPAI H5 poultry vaccination in Mexico (2022-2024).
While vaccination provided partial protection against H5N1, it was less than initially hoped for. The author's wrote:
As expected, HPAI vaccination led to a statistically higher immune response in birds in most of Mexico's states. However, seroconversion and seroprotection rates remained below 80 % during the first evaluation period.
The second round of vaccination improved seroconversion and seroprotection rates, but it still fell short of the goals. The authors explained:
A total seroconversion rate of 81.59 % was obtained for the second vaccination period, i.e., about 80 % of the vaccinated production birds mounted an immune response above 16 HAU. Four states (Campeche, Jalisco, Yucatán, and Zacatecas) obtained seroconversion rates above 80 %, while the remaining two states had seroconversion rates around 70 % (Table 3).The total seroprotection rate for this period was 76.76 %, meaning about 70 % of the vaccinated production birds in this period developed an immune response above 32 HAU. Among all states, only Campeche and Zacatecas achieved seroprotection rates above 80 % (Table 3).
First, a link, and abstract from the study, after which I'll have a postscript.
H5N1 highly pathogenic avian influenza vaccination: Seroresponse of mexican poultry in the 2022–2024
Brenda Aline Maya Badillo a b, Diana Laura García Hernández a, Rodrigo Armando Moreno García a, Guillermo Orta Pineda a b, Carlos Javier Alcázar Ramiro a, Juana Castillo Castillo a, Mario Solís Hernández a, Roberto Navarro López a 1, Armando García López a
Abstract
Since 2021, the activity and impact of the highly pathogenic H5N1 avian influenza virus have intensified worldwide, causing high mortality in wild birds and birds while also infecting various wild and domestic mammals and humans. Particularly, the severe impact on commercial poultry farming has prompted various countries to implement control and mitigation plans to address the damage caused by these viruses.In Mexico, the implementation of vaccination was part of the comprehensive strategies to prevent and control highly pathogenic H5N1 avian influenza outbreaks. For this reason, this work aimed to compare antibody levels in production birds before and after vaccination, examining seroconversion and seroprotection after vaccination in two time periods.Serum samples were taken before and after vaccination in 573 Poultry Production Units during the first vaccination period and 205 Poultry Production Units during the second period across various Mexican states. These samples, later, underwent hemagglutination inhibition tests. With the results obtained from serology, comparisons of medians, calculations of seroconversion and seroprotection, as well as logistic regression analysis were performed.As expected, vaccination led to a statistically higher immune response in birds in most of Mexico's states. However, seroconversion and seroprotection rates remained below 80 % during the first evaluation period.Progenitors and commercial posture birds showed better immune responses to vaccination, particularly with vaccines developed through reverse genetics. These results provide valuable insights into the immune response of Mexican domestic birds under the national strategic plan to control the highly pathogenic influenza A H5N1 virus emergency, which will set a precedent to improve the prevention and control of future outbreak
With vaccination campaigns, the devil is always in the details.
While seroconversion and seroprotection rates approached or exceeded 80% in many states, looking at the breakdown of the 20 states included in the first round, 7 (33%) scored considerably lower, with 2 states in single digits.
Although no detailed explanation was provided, 14 of the first round participating states were excluded from the second round (n=6) analysis, including most of the worst performers from round 1.
Challenges and limitations appear when developing national strategies for the prevention and control of infectious agents such as HPAI viruses. First, the specific monitoring of each PPU is a factor that we consider relevant.
Although most PPUs complied with the strategic vaccination plan and the requirements requested for its implementation, there were PPUs that showed weak points in this implementation and that could be seen in the serological evaluation of the immune response of the birds before and after vaccination, mainly in the calculation of the seroconversion rate and the seroprotection rate.
These limitations were evident in period one, mainly across southeastern Mexican states because they did not mount an immune response after vaccination with seroconversion and seroprotection rates less than 10 % of their population.
It is likely that some of the critical points of the vaccination plan were not fully met or were not carried out properly.
And there's the rub. Properly done - and assuming the right vaccine formulas can be developed - poultry (and possibly cattle) vaccination should become valuable tools in our fight against HPAI H5 viruses.
But as we've repeatedly seen (see Taiwan Seizes 210 Bottles of Illegal Chinese `Poultry Vaccine'), consistently maintaining that level of excellence in the real world can be a challenge
And the costs for getting it wrong - while unknowable - could be substantial.
