Vaccination of poultry against highly pathogenic avian influenza - part 1. Available vaccines and vaccination strategies

Evaluation of Different Machine Learning Approaches to Predict Antigenic Distance Among Newcastle Disease Virus (NDV) Strains

Newcastle disease virus (NDV) continues to present a significant challenge for vaccination due to its rapid evolution and the emergence of new variants. Although molecular and sequence data are now quickly and inexpensively produced, genetic distance rarely serves as a good proxy for cross-protection, while experimental studies to assess antigenic differences are time consuming and resource intensive. In response to these challenges, this study explores and compares several machine learning (ML) methods to predict the antigenic distance between NDV strains as determined by hemagglutination-inhibition (HI) assays. By analyzing F and HN gene sequences alongside corresponding amino acid features, we developed predictive models aimed at estimating antigenic distances. Among the models evaluated, the random forest (RF) approach outperformed traditional linear models, achieving a predictive accuracy with an R2 value of 0.723 compared to only 0.051 for linear models based on genetic distance alone. This significant improvement demonstrates the usefulness of applying flexible ML approaches as a rapid and reliable tool for vaccine selection, minimizing the need for labor-intensive experimental trials. Moreover, the flexibility of this ML framework holds promise for application to other infectious diseases in both animals and humans, particularly in scenarios where rapid response and ethical constraints limit conventional experimental approaches.

Immunogenicity and Protective Efficacy of Five Vaccines Against Highly Pathogenic Avian Influenza Virus H5N1, Clade 2.3.4.4b, in Fattening Geese

Background/Objectives: The risk of the introduction of highly pathogenic avian influenza virus (HPAIV) in geese breeding and fattening flocks is heightened due to the necessity of free-range access to grazing grounds. This study aimed to evaluate the safety, immunogenicity, and protective efficacy of five commercial vaccines against HPAIV subtype H5N1 (clade 2.3.4.4b) in subadult fattening geese. Methods: A prime-boost vaccination trial was conducted using five commercial vaccines, including H5 expressing vaccines of novel technology (subunit, vector, RNA) and whole inactivated virus (WIV) vaccines. Based on serological results, one RNA and one WIV vaccine were selected for a homologous challenge experiment. Results: Two vaccines of novel technology (vector, RNA) required a booster dose to raise specific antibodies titers above a threshold of four log2 using a hemagglutination inhibition (HI) assay, whereas a subunit vaccine and two WIV vaccines induced seroconversion after primary vaccination. In the challenge experiment, all unvaccinated control geese succumbed to infection by day four. In contrast, all vaccinated geese that had seroconverted exhibited full clinical protection. Although sterile immunity was not achieved, viral excretion was significantly reduced in the vaccinated groups compared to controls. Conclusions: Vaccination substantially mitigated the impact of HPAIV H5N1, clade 2.3.4.4b infection in geese, greatly improving animal welfare by preventing severe disease. Additionally, there was a significant reduction in viral burden. Further studies are necessary to verify the potential of these vaccines to reduce susceptibility to infection and virus excretion in order to achieve suppression of the between-flock reproduction number to < 1 in geese flocks at high risk of infection.

Landscape of H5 Infections in ASEAN Region: Past Insights, Present Realities, & Future Strategies

The H5 Avian Influenza A virus infection has emerged as a global concern, particularly in the ASEAN region. This viral infection poses a significant threat to the poultry industry, public health, and regional economies. This region's reliance on poultry production and the zoonotic potential of H5 subtypes, with documented transmission to various mammalian species and humans, necessitates proactive mitigation strategies. Over the years, comprehensive efforts such as surveillance, vaccination programs, biosecurity measures, and public health education have been implemented to keep outbreaks at bay. In this review, we provide a thorough overview of the H5 infections in the ASEAN region, focusing on the unique challenges and successes in this geographic area. We analyze epidemiological trends, including specific high-risk populations and transmission patterns, and assess the socioeconomic impact of H5 outbreaks on local communities. We also examine regional responses, highlighting innovative surveillance programs, vaccination strategies, and biosecurity measures implemented to control the virus. Furthermore, we explore the crucial role of the One Health approach, emphasizing interdisciplinary collaboration between human, animal, and environmental health sectors. Finally, we discuss future strategies for prevention and control, including the importance of regional cooperation in combating this evolving threat. Through this, we aim to provide valuable insights to the public, policymakers, and researchers involved in tackling H5 infections globally.

- Invited Review - Challenges and constraints to the sustainability of poultry farming in Republic of Korea

As of 2022, the Republic of Korea accounted for 0.8% of global chicken meat production and 0.9% of global egg production. The country achieved self-sufficiency rates of 83.1% for chicken meat and 99.4% for eggs, demonstrating significant quantitative and qualitative growth to meet domestic demand. Although the industry is trending towards expansion and specialization, it faces several challenges in achieving sustainable poultry production. Key challenges in Korea include highly pathogenic avian influenza and pest issues, climate change and the push for carbon neutrality, reliance on imported breeding stock, insufficient preparedness for expanding cage space per laying hen, post-settlement payment systems for egg sales and an oversupply of chicken meat, and the aging poultry farming population and the closure of farms unable to secure successors. Following strategies are proposed to overcome or mitigate challenges mentioned above: (1) enhancing farm biosecurity and implementing vaccination policies for disease control, (2) modernizing facilities and promoting carbon-neutral practices to adapt to climate change, (3) diversifying breeding stocks across multiple locations and developing domestic strains, (4) implementing policies and supporting farms based on a comprehensive readiness assessment of all farms regarding expanded cage space requirements, (5) improving market transparency for the egg industry and regulating supply and demand in the broiler industry, and (6) offering incentives for farm succession, attracting labor, and promoting coexistence between corporations, rural communities, and small farms. In conclusion, the sustainable development of Korea's poultry industry is not a simple task. It requires a comprehensive approach considering economic efficiency, animal welfare, environmental protection, food security, and the symbiosis with rural communities. This approach necessitates efficient cooperation among all stakeholders, including the government, farmers, integrators, retailers, and research institutions, along with a comprehensive, phased strategy for both short- and long-term goals.

Multivalent Inactivated Vaccine Protects Chickens from Distinct Clades of Highly Pathogenic Avian Influenza Subtypes H5N1 and H5N8

BACKGROUND/OBJECTIVE

Highly pathogenic avian influenza (HPAI) H5 subtype remains a significant menace to both the poultry industry and human public health. Biosecurity and mass vaccination of susceptible commercial poultry flocks are crucial to reduce the devastating economic loss and hinder the evolution of the virus.

METHODS

In this study, we developed a multivalent avian influenza virus (AIV) vaccine, including strains representing the HPAI 2.2.1.1., 2.2.1.2., and 2.3.4.4b clades circulating in Egypt and the Middle East. Specific pathogen-free (SPF) two-week-old chickens were vaccinated with a single vaccine shot and observed for four weeks post-vaccination before being challenged. The challenge experiment involved using one strain of HPAI H5N1 subtype clade 2.2.1.2 and two strains of HPAI H5N8 subtype clade 2.3.4.4b derived from chickens and ducks. To assess the vaccine's potency and efficacy, the pre-challenge humoral immune response and post-challenge survival and virus shedding were evaluated. Results: All the vaccinated birds exhibited 100% seroconversion 2 weeks post-vaccination (2 WPV). In addition, protective antibody titers against each diagnostic antigen, i.e., 7.8 ± 1.8 (H5N1, clade 2.2.1.2), 10.0 ± 0.0 (H5N1, clade 2.2.1.1), and 7.5 ± 0.9 (H5N8, clade 2.3.4.4b) were detected 3 WPV. The vaccination achieved complete protection (100%) against all challenge viruses with no disease symptoms. The vaccinated birds exhibited a statistically significant reduction in oropharyngeal virus shedding 2 days post-challenge (DPC).

CONCLUSIONS

This study illustrated that a single application of a multivalent genetic-matching whole AIV vaccine under laboratory conditions elicits adequate protection against the HPAI challenge, representing 2.2.1.2 and 2.3.4.4b clades. The developed vaccine has the potential to be a vaccine of choice against a broad range of HPAI in commercial flocks raised under field conditions in endemic areas.

Evaluation of humoral immune response and milk antibody transfer in calves and lactating cows vaccinated with inactivated H5 avian influenza vaccine

The detection of Highly Pathogenic Avian Influenza (HPAI) A(H5N1) in dairy cattle in the United States has raised concerns about human exposure. This study evaluated the efficacy of various doses of an inactivated H5 AI vaccine in cattle and assessed antibody transfer in milk against a recent bovine isolate of HPAI A(H5N1, clade 2.3.4.4b). Calves were inoculated with different vaccine doses, while lactating cows received the vaccine four weeks later. The humoral immune response was measured using the Hemagglutination Inhibition (HI) test and ELISA. Results showed a dose-dependent immune response, with higher doses producing stronger and more sustained antibody levels. Group 1 maintained a stable HI titer of 6 log2, while Groups 2, 3, and 4 peaked at 8, 9, and 9 log2, respectively, by the fourth week post-vaccination. Milk antibody transfer was observed, with strong positive responses in milk samples by the second week post-vaccination. The ID Screen ELISA demonstrated higher sensitivity for detecting antibodies in milk compared to serum. The immune response to the AI vaccine differed from responses to other vaccines used in cattle such as Foot and Mouth Disease Virus (FMDV) and Lumpy Skin Disease Virus (LSDV), indicating the need for optimizing vaccine dosage and formulation, including adjuvant and antigen content. Future research should extend the monitoring period, increase sample sizes, and explore different vaccine formulations to develop effective vaccination strategies for cattle. These findings highlight the potential for using inactivated H5 AI vaccines in cattle to enhance immune protection and facilitate antibody transfer through milk.

EFSA Panel on Animal Health and Animal Welfare (AHAW), ECDC, Alvarez J, Boklund A, Dippel S, Dórea F, Figuerola J, Herskin MS, Michel V, Miranda Chueca MÁ, Nannoni E, Nielsen SS, Nonno R, Riber AB, Stegeman JA, Ståhl K, Thulke H, Tuyttens F, Winckler C, Brugerolles C, Wolff T, Parys A, Lindh E, Latorre‐Margalef N, Rameix Welti M, Dürrwald R, Trebbien R, Van der Werf S, Gisslén M, Monne I, Fusaro A, Guinat C, Bortolami A, Alexakis L, Enkirch T, Svartstrom O, Willgert K, Baldinelli F, Preite L, Grant M, Broglia A, Melidou A. Preparedness, prevention and control related to zoonotic avian influenza

A risk assessment framework was developed to evaluate the zoonotic potential of avian influenza (AI), focusing on virus mutations linked to phenotypic traits related to mammalian adaptation identified in the literature. Virus sequences were screened for the presence of these mutations and their geographical, temporal and subtype-specific trends. Spillover events to mammals (including humans) and human seroprevalence studies were also reviewed. Thirty-four mutations associated with five phenotypic traits (increased receptor specificity, haemagglutinin stability, neuraminidase specificity, enhanced polymerase activity and evasion of innate immunity) were shortlisted. AI viruses (AIVs) carrying multiple adaptive mutations and traits belonged to both low and highly pathogenic subtypes, mainly to A(H9N2), A(H7N9), A(H5N6) and A(H3N8), were sporadic and primarily detected in Asia. In the EU/EEA, H5Nx viruses of clade 2.3.4.4b, which have increased opportunities for evolution due to widespread circulation in birds and occasional cases/outbreaks in mammals, have acquired the highest number of zoonotic traits. Adaptive traits, such as enhanced polymerase activity and immune evasion, were frequently acquired, while receptor-specific mutations remained rare. Globally, human cases remain rare, with the majority overall due to A(H5N1), A(H5N6), A(H7N9) and A(H9N2) that are among the subtypes that tend to have a higher number of adaptive traits. The main drivers of mammalian adaptation include virus and host characteristics, and external factors increasing AIV exposure of mammals and humans to wild and domestic birds (e.g. human activities and ecological factors). Comprehensive surveillance of AIVs targeting adaptive mutations with whole genome sequencing in animals and humans is essential for early detection of zoonotic AIVs and efficient implementation of control measures. All preparedness, preventive and control measures must be implemented under a One Health framework and tailored to the setting and the epidemiological situation; in particular, enhanced monitoring, biosecurity, genomic surveillance and global collaboration are critical for mitigating the zoonotic risks of AIV.

European Food Safety Authority (EFSA), European Centre for Disease Prevention and Control (ECDC), Adlhoch C, Alm E, Enkirch T, Lamb F, Melidou A, Willgert K, Marangon S, Monne I, Stegeman JA, Delacourt R, Baldinelli F, Broglia A. Drivers for a pandemic due to avian influenza and options for One Health mitigation measures

Avian influenza viruses (AIV) remain prevalent among wild bird populations in the European Union and European Economic Area (EU/EEA), leading to significant illness in and death of birds. Transmission between bird and mammal species has been observed, particularly in fur animal farms, where outbreaks have been reported. While transmission from infected birds to humans is rare, there have been instances of exposure to these viruses since 2020 without any symptomatic infections reported in the EU/EEA. However, these viruses continue to evolve globally, and with the migration of wild birds, new strains carrying potential mutations for mammalian adaptation could be selected. If avian A(H5N1) influenza viruses acquire the ability to spread efficiently among humans, large-scale transmission could occur due to the lack of immune defences against H5 viruses in humans. The emergence of AIV capable of infecting mammals, including humans, can be facilitated by various drivers. Some intrinsic drivers are related to virus characteristics or host susceptibility. Other drivers are extrinsic and may increase exposure of mammals and humans to AIV thereby stimulating mutation and adaptation to mammals. Extrinsic drivers include the ecology of host species, such as including wildlife, human activities like farming practices and the use of natural resources, climatic and environmental factors. One Health measures to mitigate the risk of AIV adapting to mammals and humans focus on limiting exposure and preventing spread. Key options for actions include enhancing surveillance targeting humans and animals, ensuring access to rapid diagnostics, promoting collaboration between animal and human sectors, and implementing preventive measures such as vaccination. Effective communication to different involved target audiences should be emphasised, as well as strengthening veterinary infrastructure, enforcing biosecurity measures at farms, and reducing wildlife contact with domestic animals. Careful planning of poultry and fur animal farming, especially in areas with high waterfowl density, is highlighted for effective risk reduction.

EFSA Panel on Animal Health and Animal Welfare (AHAW), European Union Reference Laboratory for Avian Influenza, Nielsen SS, Alvarez J, Bicout DJ, Calistri P, Canali E, Drewe JA, Garin‐Bastuji B, Gortázar C, Herskin MS, Michel V, Miranda Chueca MÁ, Padalino B, Roberts HC, Spoolder H, Stahl K, Velarde A, Viltrop A, Winckler C, Bortolami A, Guinat C, Harder T, Stegeman A, Terregino C, Lanfranchi B, Preite L, Aznar I, Broglia A, Baldinelli F, Gonzales Rojas JL. Vaccination of poultry against highly pathogenic avian influenza - Part 2. Surveillance and mitigation measures

Selecting appropriate diagnostic methods that take account of the type of vaccine used is important when implementing a vaccination programme against highly pathogenic avian influenza (HPAI). If vaccination is effective, a decreased viral load is expected in the samples used for diagnosis, making molecular methods with high sensitivity the best choice. Although serological methods can be reasonably sensitive, they may produce results that are difficult to interpret. In addition to routine molecular monitoring, it is recommended to conduct viral isolation, genetic sequencing and phenotypic characterisation of any HPAI virus detected in vaccinated flocks to detect escape mutants early. Following emergency vaccination, various surveillance options based on virological testing of dead birds ('bucket sampling') at defined intervals were assessed to be effective for early detection of HPAIV and prove disease freedom in vaccinated populations. For ducks, virological or serological testing of live birds was assessed as an effective strategy. This surveillance could be also applied in the peri-vaccination zone on vaccinated establishments, while maintaining passive surveillance in unvaccinated chicken layers and turkeys, and weekly bucket sampling in unvaccinated ducks. To demonstrate disease freedom with > 99% confidence and to detect HPAI virus sufficiently early following preventive vaccination, monthly virological testing of all dead birds up to 15 per flock, coupled with passive surveillance in both vaccinated and unvaccinated flocks, is recommended. Reducing the sampling intervals increases the sensitivity of early detection up to 100%. To enable the safe movement of vaccinated poultry during emergency vaccination, laboratory examinations in the 72 h prior to the movement can be considered as a risk mitigation measure, in addition to clinical inspection; sampling results from existing surveillance activities carried out in these 72 h could be used. In this Opinion, several schemes are recommended to enable the safe movement of vaccinated poultry following preventive vaccination.

PLAIN LANGUAGE SUMMARY

This publication is linked to the following EFSA Journal article: https://efsa.onlinelibrary.wiley.com/doi/10.2903/j.efsa.2023.8271.