Do commercial avian influenza H5 vaccines induce cross-reactive antibodies against contemporary H5N1 viruses in Egypt?

Evaluation of inactivated avian influenza virus and Newcastle disease virus bivalent vaccination program against newly circulated H5N8 and NDV strains

Avian influenza virus (AIV) and Newcastle disease virus (NDV) are respiratory illness syndromes that have recently been detected in vaccinated flocks and are causing major financial losses in the chicken farming industry. The objective was to evaluate the efficacy of Valley Vac H5Plus NDVg7 vaccine in protecting chickens against the H5N8 and NDV strains that have recently been circulating in comparison with the efficacy of the commercially available bivalent H5+ND7 vaccine. In contrast to the H5+ND7 vaccine, which was made of genetically distinct H5N8/2018 clade 2.3.4.4b genotype group (G5), H9N2/2016, H5N1/2017, and genetically comparable NDV genotype VII 1.1/2019 of the recently circulating challenge viruses, the Valley Vac H5Plus NDVg7 vaccine consisted of the recently isolated (RG HPAI H5N1 AIV/2015 Clade 2.2.1.2, RG HPAIV H5N8/2020 Clade 2.3.4.4b genotype group 6 (G6), and NDV genotype VII 1.1/2012) which were genetically similar to challenged strains. To determine the effectiveness of the Valley Vac H5Plus NDVg7 vaccine, a total of 70-day-old commercial chicks were divided into 7 groups of 10 birds each. Groups (G1 and G4) received Valley Vac H5Plus NDVg7 vaccine. Groups (G2 and G5) groups received commercial H5+ND7 vaccine. While groups (G3 and G6) were kept nonvaccinated, and group (G7) was kept as a nonchallenged and nonvaccinated. After 3-wk post vaccination (WPV), groups G1, G2, and G3 were challenged with A/Duck/ Egypt/SMG4/2019(H5N8) genotype G6. On the other hand, groups G4, G5, G6 were challenged with NDV/EGYPT/18629F/2018 genotype VII 1.1 with an intranasal injection of 0.1 mL. Antibody titer was calculated at the first 3 wk after vaccination, and the viral shedding titer was calculated at 3-, 5-, and 7-days post challenge. Mortality and morbidity rates were monitored daily during the experiment, and for the first 10 d after the challenge, to provide an estimate of the protection rate. The results showed that a single dosage of 0.5 mL per bird of Valley Vac H5Plus NDVg7 vaccine provides 80% protection against both H5N8 and NDV, compared to the bivalent H5+ND7 vaccine, which provided 20 and 80% protection against H5N8 and NDV, respectively. In addition, 0.5 mL per bird of Valley Vac H5Plus NDVg7 vaccine produced a greater immune response against both viruses than commercial vaccination at 1 to 3 WPV with a significant difference at 1 WPV for H5N8 and a comparatively higher immune response for NDV. Furthermore, it reduced virus shedding of H5N8 on the third, fifth, seventh, and tenth days lower than H5+ND7 vaccine with a significant difference on the third day for H5N8 and relatively lower than bivalent H5+ND7 vaccine for NDV with a significant difference on the fifth day. The Valley vaccinated group demonstrated more tissue intactness compared to the commercially vaccinated group against the H5N8 challenge, however the bivalent commercially vaccinated group showed the similar level of tissue integrity against NDV. In conclusion, Valley Vac H5Plus NDVg7  that contains the  genetically similar strain to recently circulating challenged virus (H5N8 genotype G6) provided better protection with greater immune response and decreased the amount of virus shed against H5N8 genotype G6 and showed less histopathological alteration than the commercial bivalent H5+ND7 vaccine that contain genetically distinct (H5N8 genotype G5). However the Valley Vac H5Plus NDVg7 provided the same protection with relatively high immune response and  relatively decreased the amount of virus shed and showed equal tissue integrity than the commercial bivalent H5+ND7 vaccine against NDV genotype VII 1.1 that contain the same genotype of NDV genotype VII 1.1.

The molecular basis of differential host responses to avian influenza viruses in avian species with differing susceptibility

Introduction

Highly pathogenic avian influenza (HPAI) viruses, such as H5N1, continue to pose a serious threat to animal agriculture, wildlife and to public health. Controlling and mitigating this disease in domestic birds requires a better understanding of what makes some species highly susceptible (such as turkey and chicken) while others are highly resistant (such as pigeon and goose). Susceptibility to H5N1 varies both with species and strain; for example, species that are tolerant of most H5N1 strains, such as crows and ducks, have shown high mortality to emerging strains in recent years. Therefore, in this study we aimed to examine and compare the response of these six species, to low pathogenic avian influenza (H9N2) and two strains of H5N1 with differing virulence (clade 2.2 and clade 2.3.2.1) to determine how susceptible and tolerant species respond to HPAI challenge.

Methods

Birds were challenged in infection trials and samples (brain, ileum and lung) were collected at three time points post infection. The transcriptomic response of birds was examined using a comparative approach, revealing several important discoveries.

Results

We found that susceptible birds had high viral loads and strong neuro-inflammatory response in the brain, which may explain the neurological symptoms and high mortality rates exhibited following H5N1 infection. We discovered differential regulation of genes associated with nerve function in the lung and ileum, with stronger differential regulation in resistant species. This has intriguing implications for the transmission of the virus to the central nervous system (CNS) and may also indicate neuro-immune involvement at the mucosal surfaces. Additionally, we identified delayed timing of the immune response in ducks and crows following infection with the more deadly H5N1 strain, which may account for the higher mortality in these species caused by this strain. Lastly, we identified candidate genes with potential roles in susceptibility/resistance which provide excellent targets for future research.

Discussion

This study has helped elucidate the responses underlying susceptibility to H5N1 influenza in avian species, which will be critical in developing sustainable strategies for future control of HPAI in domestic poultry.

H5 Influenza Viruses in Egypt

For almost a decade, Egypt has been endemic for highly pathogenic avian influenza (HPAI) A(H5N1) viruses. In addition to being catastrophic for poultry production, A(H5N1) has also caused 359 human infections in the country (∼40% of global cases), with 120 being fatal. From 2017, A(H5N1) viruses have been gradually replaced by HPAI A(H5N8) viruses seeded from Southeast Asia through Europe; no human cases have been reported since. This lack of human cases is not a consequence of fewer H5 infections in poultry. Despite governmental outbreak control, the number of avian influenza outbreaks has increased since 2006 partially fueled by noncompliance with preventive measures and suboptimal vaccination programs. Adherence to control measures is low because of social norms, especially among women and children-the main caretakers of household flocks in rural areas-and declining public awareness in the community. Egypt has thus become an epicenter for A(H5) virus evolution, with no clear resolution in sight.

Herpesvirus of turkey-vectored avian influenza vaccine offers cross-protection against antigenically drifted H5Nx highly pathogenic avian influenza virus strains

Among the different vaccines used to control highly pathogenic avian influenza, an HVT vector-based live recombinant avian influenza vaccine, expressing the haemagglutinin gene of an H5N1 HPAI virus, has been used by the poultry industry since 2012. The objective of the study presented in this paper was to test the efficacy of the commercially available HVT-based recombinant H5 vaccine against antigenically drifted H5N1, H5N8 and H5N2 HPAI virus circulating in Egypt recently. Groups of SPF chicks vaccinated at day-old with the HVT-based recombinant H5 vaccine were challenged, along with non-vaccinated controls, with 10⁶ EID₅₀ each of H5N1, H5N2 or H5N8 HPAI virus at 28 days of age. The birds were monitored for clinical protection and virus shedding during a 10-day postchallenge period. Clinical protection levels were 90%, 90% and 80% following challenge with the H5N1, H5N2 and H5N8 field isolates, respectively. Challenge virus shedding was significantly reduced in vaccinated groups, with up to 40%, 30% and 20% of non-shedders, and 3.8, 3.3 and 2.8 log₁₀ reduction in the amount of excreted virus following challenge with H5N1, H5N2 and H5N8 viruses, respectively. Analyses of the amino acid sequences of the HA proteins of challenge viruses and serological relatedness with the vaccine insert revealed significant antigenic divergences between the vaccine and the challenge viruses. These results provide further evidence of the potential of HVT-based recombinant H5 vaccine to provide cross-protection against antigenically drifted HPAI H5Nx viruses with strong control on virus shedding.

Development of an effective contemporary trivalent avian influenza vaccine against circulating H5N1, H5N8, and H9N2 in Egypt

Low pathogenicity avian influenza (LPAI) H9N2, highly pathogenic avian influenza (HPAI) H5N1, and H5N8 circulate in Egyptian poultry and cause veterinary and public health burdens. In response, AIV vaccines are commonly used. The main objective of this study was to develop a broad, cross-protective, trivalent vaccine based on circulating AIVs in Egypt. We generated highly replicating avirulent AIVs, H5N1, and H5N8, to be used in combination with H9N2 strain for the generation of an inactivated vaccine. Immunogenicity and protective efficacy of this vaccine were tested. Results showed that a single immunization dose enhanced humoral immune responses giving full protection against challenges with LPAI H9N2, HPAI H5N1, and H5N8 viruses. This efficacious vaccine will reduce the cost of vaccination for poultry growers and is expected to be effective in the field as it is based on contemporary viruses currently in circulation among Egyptian poultry.

Developing Farm-Level Post-vaccination Sero-Monitoring Systems for H5N1 Highly Pathogenic Avian Influenza in an Endemically Infected Country

Whilst the serological responses of poultry following vaccination against highly pathogenic avian influenza H5N1 has been extensively investigated under laboratory conditions, there have been fewer studies conducted in the field. This applies particularly to the endemically infected countries routinely practicing vaccination, where the combination of multiple circulating clades and/or the use of vaccines with different seed strains makes the design and interpretation of field studies especially problematic. To address this for the particular situation of layer hens in the small to medium commercial sector in Indonesia, we developed a sampling regime before and after the vaccination given to point-of-lay pullets, and assessed serological response with a panel of test antigens. This confirmed that high titres were induced in those birds vaccinated with locally produced homologous H5N1 vaccines administered two or more times, but in flocks using imported heterologous H5N2 vaccines median titres were significantly lower, and unlikely to provide protection throughout the production cycle, without additional vaccination. Comparing the HI responses against the panel of antigens enabled the detection of the flock's exposure to different vaccine antigens, and made possible the detection of mislabelled vaccine seed strains. Furthermore, we show that test antigens need not be exactly matched to assess sero-protection in well vaccinated birds. Finally our study suggests that the POL vaccination serves as a useful reference point for following cohorts of layers throughout their production cycle, and thus enabling robust vaccination field effectiveness studies.

Efficacy of a Recombinant Turkey Herpesvirus AI (H5) Vaccine in Preventing Transmission of Heterologous Highly Pathogenic H5N8 Clade 2.3.4.4b Challenge Virus in Commercial Broilers and Layer Pullets

Outbreaks caused by the highly pathogenic avian influenza virus (HPAIV) H5N8 subtype clade 2.3.4.4 were first reported in 2014 in South Korea then spread very rapidly in Asia, to Europe, and for the first time, to North America. Efficacy of a recombinant HVT-AI (H5) vaccine (rHVT-H5) to provide clinical protection as well as to significantly reduce the shedding of an H5N8 challenge virus has already been demonstrated in SPF chickens. The aim of our studies was to test the efficacy of the same rHVT-H5 vaccine in controlling the transmission of a recent Hungarian HPAIV H5N8 challenge virus in commercial chickens. Broilers and layers were vaccinated at day old according to the manufacturer's recommendation and then challenged with a 2017 Hungarian HPAIV H5N8 (2.3.4.4b) isolate at 5 or 7 weeks of age, respectively. Evaluation of clinical protection, reduction of challenge virus shedding, and transmission to vaccinated contact birds was done on the basis of clinical signs/mortality, detection, and quantitation of challenge virus in oronasal and cloacal swabs (regularly between 1 and 14 days postchallenge). Measurement of seroconversion to AIV nucleoprotein was used as an indicator of infection and replication of challenge virus. Our results demonstrated that rHVT-H5 vaccination could prevent the development of clinical disease and suppress shedding very efficiently, resulting in the lack of challenge virus transmission to vaccinated contact chickens, regardless the type of birds. Single immunization with the tested rHVT-H5 vaccine proved to be effective to stop HPAIV H5N8 (2.3.4.4b) transmission within vaccinated poultry population under experimental conditions.

Zoonotic Potential of Influenza A Viruses: A Comprehensive Overview

Influenza A viruses (IAVs) possess a great zoonotic potential as they are able to infect different avian and mammalian animal hosts, from which they can be transmitted to humans. This is based on the ability of IAV to gradually change their genome by mutation or even reassemble their genome segments during co-infection of the host cell with different IAV strains, resulting in a high genetic diversity. Variants of circulating or newly emerging IAVs continue to trigger global health threats annually for both humans and animals. Here, we provide an introduction on IAVs, highlighting the mechanisms of viral evolution, the host spectrum, and the animal/human interface. Pathogenicity determinants of IAVs in mammals, with special emphasis on newly emerging IAVs with pandemic potential, are discussed. Finally, an overview is provided on various approaches for the prevention of human IAV infections.

Efficacy of commercial vaccines against newly emerging avian influenza H5N8 virus in Egypt

The newly emerging, highly pathogenic avian influenza (HPAI) H5N8 virus of clade 2.3.4.4 was recently detected in wild birds and domestic poultry in Egypt in the 2016/2017 winter season. Vaccination based on commercial H5 vaccines is used as an essential control strategy in Egyptian poultry. Here, we studied the efficacy of the eight most common commercial H5 poultry vaccines in the Egyptian market and compared them with an experimental vaccine based on the Egyptian LPAI H5N8 virus that was prepared by using reverse genetics. The experimental vaccine and Re-5 commercial vaccine were able to completely protect chickens and significantly reduce virus shedding. Our results indicate that most of the commercial poultry H5 vaccines used in the present study were ineffective because the seed viruses in these vaccines are genetically distinct from the H5N8 viruses currently circulating in Egypt. Although some of the commercial vaccines protected chickens from mortality, they failed to prevent chickens from shedding the virus. Accordingly, we recommend updating and reinforcing the H5N8 prevention and control strategies in Egypt. The vaccination strategy should be reconsidered based on currently circulating viruses.

Avian influenza H5N1 vaccination efficacy in Egyptian backyard poultry

Raising backyard poultry under low biosecurity conditions is a common practice in Egypt. While vaccination is routinely applied in Egypt in commercial settings to curb the spread of avian influenza viruses, it remains less commonly used in backyard settings. We assessed the immunogenicity and protective efficacy of a H5N1 vaccine based on a contemporary Egyptian clade 2.2.1.2 virus among turkeys, ducks, geese, and chickens raised together in a backyard setting. Results showed that this vaccine elicits an immune response in all tested species reaching up to a hemagglutination inhibition titer of 10 log₂ after a booster dose. However, this response varied between species. When challenged, vaccinated birds survived and shed less virus in comparison with unvaccinated birds. However, unvaccinated ducks showed no symptoms of infection and survived the duration of the experiment. Moreover, vaccinated ducks shed more virus as compared to vaccinated birds of other species. Hence, we recommend avoiding mixing various species in the backyards of Egypt. Our data indicates that vaccination can be effective in the backyard setting in Egypt, although planning should consider the species covered.

Selection of antigenic variants of an H5N1 highly pathogenic avian influenza virus in vaccinated chickens

Vaccination-primed immunity in poultry has been suggested for selection of antigenically drifted highly pathogenic avian influenza viruses (HPAIVs). In this study, we performed two consecutive passage studies of an H5N1 HPAIV in vaccinated chickens, namely, study-I and study-II, to select antigenic variants under immune pressure from the vaccination. In study-I, nine consecutive passages of a wild-type H5N1 HPAIV were carried out in chickens vaccinated with the homologous challenge strain. Antigenically drifted variants with mutations at position 179 in the hemagglutinin (HA) were selected after three passages. Similarly, in study-II, a vaccination-mediated antigenic variant isolated in study-I was used as the vaccine and challenge strain to confirm further antigenic drift after updating the vaccine; after the third passage, additional antigenic variants with a mutation at position 256 in the HA were selected. Thus, our study demonstrated the contribution of vaccination in the selection of antigenic variants of H5 HPAIVs in chickens.

Genetic characterization of highly pathogenic avian influenza A H5N8 viruses isolated from wild birds in Egypt

A newly emerged H5N8 influenza virus was isolated from green-winged teal in Egypt during December 2016. In this study, we provide a detailed characterization of full genomes of Egyptian H5N8 viruses and some virological features. Genetic analysis demonstrated that the Egyptian H5N8 viruses are highly pathogenic avian influenza viruses. Phylogenetic analysis revealed that the genome of the Egyptian H5N8 viruses was related to recently characterized reassortant H5N8 viruses of clade 2.3.4.4 isolated from different Eurasian countries. Multiple peculiar mutations were characterized in the Egyptian H5N8 viruses, which probably permits transmission and virulence of these viruses in mammals. The Egyptian H5N8 viruses preferentially bound to avian-like receptors rather than human-like receptors. Also, the Egyptian H5N8 viruses were fully sensitive to amantadine and neuraminidase inhibitors. Chicken sera raised against commercial inactivated avian influenza-H5 vaccines showed no or very low reactivity with the currently characterized H5N8 viruses in agreement with the genetic dissimilarity. Surveillance of avian influenza in waterfowl provides early warning of specific threats to poultry and human health and hence should be continued.

Immunopotentiators Improve the Efficacy of Oil-Emulsion-Inactivated Avian Influenza Vaccine in Chickens, Ducks and Geese

Combination of CVCVA5 adjuvant and commercial avian influenza (AI) vaccine has been previously demonstrated to provide good protection against different AI viruses in chickens. In this study, we further investigated the protective immunity of CVCVA5-adjuvanted oil-emulsion inactivated AI vaccine in chickens, ducks and geese. Compared to the commercial H5 inactivated vaccine, the H5-CVCVA5 vaccine induced significantly higher titers of hemaglutinin inhibitory antibodies in three lines of broiler chickens and ducks, elongated the antibody persistence periods in geese, elevated the levels of cross serum neutralization antibody against different clade and subclade H5 AI viruses in chicken embryos. High levels of mucosal antibody were detected in chickens injected with the H5 or H9-CVCA5 vaccine. Furthermore, cellular immune response was markedly improved in terms of increasing the serum levels of cytokine interferon-γ and interleukine 4, promoting proliferation of splenocytes and upregulating cytotoxicity activity in both H5- and H9-CVCVA5 vaccinated chickens. Together, these results provide evidence that AI vaccines supplemented with CVCVA5 adjuvant is a promising approach for overcoming the limitation of vaccine strain specificity of protection.

Introduction and enzootic of A/H5N1 in Egypt: Virus evolution, pathogenicity and vaccine efficacy ten years on

It is almost a decade since the highly pathogenic H5N1 avian influenza virus (A/H5N1) of clade 2.2.1 was introduced to Egypt in 2005, most likely, via wild birds; marking the longest endemic status of influenza viruses in poultry outside Asia. The endemic A/H5N1 in Egypt still compromises the poultry industry, poses serious hazards to public health and threatens to become potentially pandemic. The control strategies adopted for A/H5N1 in Egyptian poultry using diverse vaccines in commercialized poultry neither eliminated the virus nor did they decrease its evolutionary rate. Several virus clades have evolved, a few of them disappeared and others prevailed. Disparate evolutionary traits in both birds and humans were manifested by accumulation of clade-specific mutations across viral genomes driven by a variety of selection pressures. Viruses in vaccinated poultry populations displayed higher mutation rates at the immunogenic epitopes, promoting viral escape and reducing vaccine efficiency. On the other hand, viruses isolated from humans displayed changes in the receptor binding domain, which increased the viral affinity to bind to human-type glycan receptors. Moreover, viral pathogenicity exhibited several patterns in different hosts. This review aims to provide an overview of the viral evolution, pathogenicity and vaccine efficacy of A/H5N1 in Egypt during the last ten years.

Supplementation of oil-based inactivated H9N2 vaccine with M2e antigen enhances resistance against heterologous H9N2 avian influenza virus infection

Avian influenza virus (AIV) subtype H9N2 has been evolving rapidly and vaccine escape variants have been reported to cause circulation of infections and economic losses. In the present study, we developed and evaluated ectodomain of the AIV matrix 2 (M2e) protein as a supplementing antigen for oil-based inactivated H9N2 vaccine to increase resistance against vaccine escape variants. AIV H9N2 M2e antigen was expressed in Escherichia coli and supplemented to inactivated H9N2 oil emulsion vaccine. Specific pathogen-free chickens received a single injection of inactivated H9N2 oil emulsion vaccines with or without M2e supplementation. At three weeks post vaccination, hemagglutination inhibition tests and enzyme-linked immunosorbent assays were performed to determine serological immune responses. Challenge study using a vaccine escape H9N2 variant was performed to evaluate the efficacy of M2e supplementation. M2e antigen supplemented in oil emulsion vaccine was highly immunogenic, and a single M2e-supplemented vaccination reduced challenge virus replication and shedding more effectively than non-supplemented vaccination.

Comparative serological assays for the study of h5 and h7 avian influenza viruses

The nature of influenza virus to randomly mutate and evolve into new types is an important challenge in the control of influenza infection. It is necessary to monitor virus evolution for a better understanding of the pandemic risk posed by certain variants as evidenced by the highly pathogenic avian influenza (HPAI) viruses. This has been clearly recognized in Egypt following the notification of the first HPAI H5N1 outbreak. The continuous circulation of the virus and the mass vaccination programme undertaken in poultry have resulted in a progressive genetic evolution and a significant antigenic drift near the major antigenic sites. In order to establish if vaccination is sufficient to provide significant intra- and interclade cross-protection, lentiviral pseudotypes derived from H5N1 HPAI viruses (A/Vietnam/1194/04, A/chicken/Egypt-1709-01/2007) and an antigenic drift variant (A/chicken/Egypt-1709-06-2008) were constructed and used in pseudotype-based neutralization assays (pp-NT). pp-NT data obtained was confirmed and correlated with HI and MN assays. A panel of pseudotypes belonging to influenza Groups 1 and 2, with a combination of reporter systems, was also employed for testing avian sera in order to support further application of pp-NT as an alternative valid assay that can improve avian vaccination efficacy testing, vaccine virus selection, and the reliability of reference sera.

Vaccination with recombinant RNA replicon particles protects chickens from H5N1 highly pathogenic avian influenza virus

Highly pathogenic avian influenza viruses (HPAIV) of subtype H5N1 not only cause a devastating disease in domestic chickens and turkeys but also pose a continuous threat to public health. In some countries, H5N1 viruses continue to circulate and evolve into new clades and subclades. The rapid evolution of these viruses represents a problem for virus diagnosis and control. In this work, recombinant vesicular stomatitis virus (VSV) vectors expressing HA of subtype H5 were generated. To comply with biosafety issues the G gene was deleted from the VSV genome. The resulting vaccine vector VSV*ΔG(HA) was propagated on helper cells providing the VSV G protein in trans. Vaccination of chickens with a single intramuscular dose of 2×10⁸ infectious replicon particles without adjuvant conferred complete protection from lethal H5N1 infection. Subsequent application of the same vaccine strongly boosted the humoral immune response and completely prevented shedding of challenge virus and transmission to sentinel birds. The vaccine allowed serological differentiation of infected from vaccinated animals (DIVA) by employing a commercially available ELISA. Immunized chickens produced antibodies with neutralizing activity against multiple H5 viruses representing clades 1, 2.2, 2.5, and low-pathogenic avian influenza viruses (classical clade). Studies using chimeric H1/H5 hemagglutinins showed that the neutralizing activity was predominantly directed against the globular head domain. In summary, these results suggest that VSV replicon particles are safe and potent DIVA vaccines that may help to control avian influenza viruses in domestic poultry.