Success factors for avian influenza vaccine use in poultry and potential impact at the wild bird-agricultural interface

Efficacy of live and inactivated recombinant Newcastle disease virus vaccines expressing clade 2.3.4.4b H5 hemagglutinin against H5N1 highly pathogenic avian influenza in SPF chickens, Broilers, and domestic ducks

A Newcastle disease virus (NDV)-vectored vaccine expressing clade 2.3.4.4b H5 Hemagglutinin was developed and assessed for efficacy against H5N1 highly pathogenic avian influenza (HPAI) in specific pathogen-free (SPF) chickens, broilers, and domestic ducks. In SPF chickens, the live recombinant NDV-vectored vaccine, rK148/22-H5, achieved complete survival against HPAI and NDV challenges and significantly reduced viral shedding. Notably, the live rK148/22-H5 vaccine conferred good clinical protection in broilers despite the presence of maternally derived antibodies. Good clinical protection was observed in domestic ducks, with decreased viral shedding. It demonstrated complete survival and reduced cloacal viral shedding when used as an inactivated vaccine from SPF chickens. The rK148/22-H5 vaccine is potentially a viable and supportive option for biosecurity measure, effectively protecting in chickens against the deadly clade 2.3.4.4b H5 HPAI and NDV infections. Furthermore, it aligns with the strategy of Differentiating Infected from Vaccinated Animals (DIVA).

Re-evaluating efficacy of vaccines against highly pathogenic avian influenza virus in poultry: A systematic review and meta-analysis

The global spread of highly pathogenic avian influenza (HPAI) A (H5N1) clade 2.3.4.4b virus since 2021 necessitates a re-evaluation of the role of vaccination in controlling HPAI outbreaks among poultry, which has been controversial because of the concern of silent spread with viral mutation and spillover to human. We systematically reviewed and meta-analyzed all existing data from experimental challenge trials to assess the efficacy of HPAI vaccines against mortality in specific pathogen free (SPF) chickens, with evaluation of the certainty of evidence (CoE) using the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) approach. Out of 223 screened publications, 46 trials met our eligibility criteria. Inactivated vaccines showed an efficacy of 95% (risk ratio [RR] = 5% [95% CI: 1% to 17%], I2 = 0%, CoE high) against homologous strains and an efficacy of 78% (RR = 22% [95% CI: 14% to 37%], I2 = 18%, CoE high) against heterologous strains (test for subgroup difference p = 0.02). Live recombinant vaccines exhibited the highest efficacy at 97% (RR = 3% [95% CI: 1% to 13%], I2 = 0%, CoE high). Inactivated recombinant vaccines had an overall efficacy of 90% (RR = 10% [95% CI: 6% to 16%], I2 = 47%, CoE high). Commercial vaccines showed an overall efficacy of 91% (RR = 9% [95% CI: 5% to 17%], I2 = 23%, CoE high), with 96% efficacy (RR = 4% [95% CI: 1% to 21%], I2 = 0%, CoE high) against homologous strains and 90% efficacy (RR = 10% [95% CI: 5% to 20%], I2 = 31%, CoE moderate) against heterologous strains. Our systematic review offers an updated and unbiased assessment of vaccine efficacy against HPAI-related mortality, providing timely and crucial information for re-evaluating the role of vaccination in poultry avian influenza control policy amist the global HPAI outbreak post-2021.

Vaccination of African penguins (Spheniscus demersus) against high-pathogenicity avian influenza

BACKGROUND

High-pathogenicity avian influenza (HPAI) has become a conservation threat to wild birds. Therefore, suitable vaccine technology and practical application methods require investigation.

METHODS

Twenty-four African penguins (Spheniscus demersus) were vaccinated with either a conventional inactivated clade 2.3.4.4b H5N8 HPAI whole virus or a tobacco leaf-produced H5 haemagglutinin-based virus-like particle (VLP). Six birds received a second dose of the inactivated vaccine. Antibody responses were assessed and compared by employing haemagglutination inhibition tests.

RESULTS

A second dose of inactivated vaccine was required to induce antibody titres above the level required to suppress virus shedding, while a single dose of VLP vaccine produced these levels by day 14, and one bird still had antibodies on day 430.

LIMITATIONS

Bacterial contamination of the VLP vaccine limited the monitoring period and sample size in that treatment group, and it was not possible to perform a challenge study with field virus.

CONCLUSION

VLP vaccines offer a more practical option than inactivated whole viruses, especially in logistically challenging situations involving wild birds.

The influence of Spirulina extract on pathogenicity, immune response, and vaccine efficacy against H9N2 avian influenza virus in specific pathogen free chickens

Avian influenza (AI) viruses pose a risk to the worldwide poultry industry. Ultimately, improving the efficiency of the H9N2 vaccine is necessary to better control low-pathogenic avian influenza-H9N2 by using natural immunostimulant. Therefore, the goal of the present study was to examine varying doses of the cyanobacterium Spirulina extract on the effectiveness of H9N2 vaccine. Thus, a total of 150 specific pathogen-free (SPF) chickens were allocated into 6 groups, 25 birds each, as follow: G1, G2, and G6 were supplemented with 200, 400, and 400 mg Spirulina extract/kg feed, respectively, whilst the feed in G3, G4, and G5 were not supplemented with Spirulina extract. At 21-days-old, only the chickens in G1, G2, and G3 were vaccinated with the H9N2 AI vaccine. After 4 wk postvaccination, the chickens in G1, G2, G3, G4, and G6 were challenged with H9N2 AI Egyptian strain. The challenged virus was selected from a recent circulating Egyptian strain during 2022, and it was related to A/quail/Hong Kong/G1/97-like virus lineage and clustered with G1-B sub-lineage EGY-2 group. It had a high amino acids identity percentage of 92.6% with the A/chicken/Iran/av1221/1998 (Boehringer Ingelheim) vaccine. The results of real-time reverse-transcriptase polymerase-chain-reaction (rRT-PCR) revealed that no shedding of the virus was reported in G1, G2, G3, and G5. The supplementation of Spirulina extract in low (200 mg/kg of feed) and high (400 mg/kg of feed) concentration with the birds vaccinated with H9N2 AI vaccine (G1 and G2) induced prominent immuno-stimulatory effect in a dose dependent manner where it strongly enhanced the phagocytic activities of broilers' peripheral blood monocytes, and lysozyme at all days postvaccination (dpv) and days postchallenge (dpc) compared to other groups with significant differences at all day of experiment and 21st dpv, 28th dpv, 7th dpc, and 14th dpc, respectively. The supplementation with Spirulina extract in G1 and G2 induced the highest hemagglutination inhibition antibody titer in a dose-dependent manner at all-time intervals. The antibody titer postvaccination was significantly increased in G1 and G2 at 14th, and 21st dpv, in comparison with G3. Furthermore, G1 and G2 showed higher significant antibody titers at 7th and 14th dpc, compared to other groups. Furthermore, Spirulina extract (200 and 400 mg/kg feed) in G1 and G2 showed anti-inflammatory effect in a dose dependant manner by downregulating nitric oxide levels at all times postchallenge with a significant difference at 3 to 7 dpc compared to G3, G4, and G6, with improved histopathological alterations in the trachea, lung, kidney, spleen, and bursa of Fabricius.  G6 supplied with 400 mg/kg Spirulina extract feed only without vaccination had a similar effect as vaccinated groups on innate immunity. However, it delayed the production of antibodies and did not prevent viral shedding as in vaccinated groups. In conclusion, vaccination in conjunction with either dose of Spirulina extract (G1, and G2) prevents viral shedding, increases the immune response, and reduces inflammation and histopathological change caused by H9N2 AI infection in a dose dependent manner. We recommend the use of 400 mg Spirulina extract/kg feed as a natural immunostimulant in conjunction with the H9N2 vaccine to achieve the highest possible level of protection against H9N2 AI infection.

Efficacy of recombinant H5 vaccines delivered in ovo or day of age in commercial broilers against the 2015 U.S. H5N2 clade 2.3.4.4c highly pathogenic avian Influenza virus

BACKGROUND

Avian influenza is a highly contagious, agriculturally relevant disease that can severely affect the poultry industry and food supply. Eurasian-origin H5Nx highly pathogenic avian influenza viruses (HPAIV) (clade 2.3.4.4) have been circulating globally in wild birds with spill over into commercial poultry operations. The negative impact to commercial poultry renewed interest in the development of vaccines against these viruses to control outbreaks in the U.S.

METHODS

The efficacy of three recombinant H5 vaccines delivered in ovo or day of age were evaluated in commercial broilers challenged with the 2015 U.S. H5N2 clade 2.3.4.4c HPAIV. The recombinant vaccines included an alphavirus RNA particle vaccine (RP-H5), an inactivated reverse genetics-derived (RG-H5) and recombinant HVT vaccine (rHVT-AI) expressing H5 hemagglutinin (HA) genes. In the first experiment, in ovo vaccination with RP-H5 or rHVT-AI was tested against HPAI challenge at 3 or 6 weeks of age. In a second experiment, broilers were vaccinated at 1 day of age with a dose of either 107 or 108 RP-H5, or RG-H5 (512 HA units (HAU) per dose).

RESULTS

In experiment one, the RP-H5 provided no protection following in ovo application, and shedding titers were similar to sham vaccinated birds. However, when the RP-H5 was delivered in ovo with a boost at 3 weeks, 95% protection was demonstrated at 6 weeks of age. The rHVT-AI vaccine demonstrated 95 and 100% protection at 3 and 6 weeks of age, respectively, of challenged broilers with reduced virus shedding compared to sham vaccinated birds. Finally, when the RP-H5 and rHVT vaccines were co-administered at one day of age, 95% protection was demonstrated with challenge at either 3 or 6 weeks age. In the second experiment, the highest protection (92%) was observed in the 108 RP-H5 vaccinated group. Significant reductions (p < 0.05) in virus shedding were observed in groups of vaccinated birds that were protected from challenge. The RG-H5 provided 62% protection from challenge. In all groups of surviving birds, antibody titers increased following challenge.

CONCLUSIONS

Overall, these results demonstrated several strategies that could be considered to protected broiler chickens during a H5 HPAI challenge.

Evaluation of the immuno-stimulatory effect of aqueous neem (Azadirachta indica) leaf extract against highly pathogenic avian influenza (H5N8) in experimental chickens

The recently detected clade 2.3.4.4 of the highly pathogenic avian influenza (HPAI) H5N8 virus in poultry encouraged us to study the efficacy of the 6 most extensively used saleable H5 poultry vaccinations (bivalent [AI + ND], Re-5 H5N1, H5N1, H5N3, monovalent AI, monovalent ND) with or without aqueous 8% neem (Azadirachta indica) leaf extract as an immunostimulant. One hundred thirty birds were randomly divided into 7 groups. Groups 1, 2, 3, 4, 5, and 6 were divided into 2 subgroups (G1a, G2a, G3a, G4a, G5a, G6a) and (G1b, G2b, G3b, G4b, G5b, G6b) with 10 birds each. Subgroups (G1a, G2a, G3a, G4a, G5a, G6a) received the (bivalent [AI + ND], Re-H5N1, H5N1, H5N3, monovalent AI, monovalent ND) vaccines, while subgroups (G1b, G2b, G3b, G4b, G5b, G6b) received the same previous vaccination but treated with neem leaf extract administrated 2 d before and after vaccination, and G7 with 10 birds was kept unvaccinated as positive control group. Clinical signs of the challenged group showed conjunctivitis, closed eyes, cyanosis in comb and wattle, ocular discharge, and greenish diarrhea, while postmortem lesions showed congested trachea and lung, hemorrhage on the shank, proventriculus, and pancreas; gelatinous fluid submandibular, congestion of all organs (septicemia), mottled spleen. The clinical signs and lesions were mild in neem leaf extract treated with bivalent vaccine and Re-H5N1 while moderate in monovalent vaccine and H5N3 with or without neem leaf extract treated and reached severe in the group immunized with H5N1 with or without neem leaf extract treatment. The protection levels in the bivalent vaccine (AI + ND), Re-5 H5N1, and H5N3 treated with neem leaf extract, were 80%, 80%, and 60%, respectively, while bivalent vaccine (AI + ND), Re-5 H5N1 and H5N3 without treatment were 60%, 60%, and 40%, respectively. The virus shedding was prevented in groups vaccinated with bivalent vaccine and Re-H5N1 vaccine treated with neem leaf extract, while decreased in the group vaccinated with H5N3 with neem leaf extract and Re-H5N1 without neem leaf extract compared with H5N3, H5N1, and monovalent vaccine. The immunological response after vaccination was stronger in the bivalent vaccine group than in the other commercial vaccine groups treated with neem leaf extract, with geometric mean titer (GMTs) of 315.2 and 207.9 at the third and fourth weeks, respectively. The use of immunostimulant antiviral medicinal plants, such as neem, completely protected chicken flocks against HPAI (H5N8) and prevented AI virus shedding, leading us to the conclusion that the use of bivalent vaccines induces a higher immune response than other different commercial vaccines.

A systematic review of mechanistic models used to study avian influenza virus transmission and control

The global spread of avian influenza A viruses in domestic birds is causing increasing socioeconomic devastation. Various mechanistic models have been developed to better understand avian influenza transmission and evaluate the effectiveness of control measures in mitigating the socioeconomic losses caused by these viruses. However, the results of models of avian influenza transmission and control have not yet been subject to a comprehensive review. Such a review could help inform policy makers and guide future modeling work. To help fill this gap, we conducted a systematic review of the mechanistic models that have been applied to field outbreaks. Our three objectives were to: (1) describe the type of models and their epidemiological context, (2) list estimates of commonly used parameters of low pathogenicity and highly pathogenic avian influenza transmission, and (3) review the characteristics of avian influenza transmission and the efficacy of control strategies according to the mechanistic models. We reviewed a total of 46 articles. Of these, 26 articles estimated parameters by fitting the model to data, one evaluated the effectiveness of control strategies, and 19 did both. Values of the between-individual reproduction number ranged widely: from 2.18 to 86 for highly pathogenic avian influenza viruses, and from 4.7 to 45.9 for low pathogenicity avian influenza viruses, depending on epidemiological settings, virus subtypes and host species. Other parameters, such as the durations of the latent and infectious periods, were often taken from the literature, limiting the models' potential insights. Concerning control strategies, many models evaluated culling (n = 15), while vaccination received less attention (n = 6). According to the articles reviewed, optimal control strategies varied between virus subtypes and local conditions, and depended on the overall objective of the intervention. For instance, vaccination was optimal when the objective was to limit the overall number of culled flocks. In contrast, pre-emptive culling was preferred for reducing the size and duration of an epidemic. Early implementation consistently improved the overall efficacy of interventions, highlighting the need for effective surveillance and epidemic preparedness.

Prediction of highly pathogenic avian influenza vaccine efficacy in chickens by comparison of in vitro and in vivo data: A meta-analysis and systematic review

Vaccines for avian influenza (AI) can protect poultry against disease, mortality, and virus transmission. Numerous factors, including: vaccine platform, immunogenicity, and relatedness to the field strain, are known to be important to achieving optimal AI vaccine efficacy. To better understand how these factors contribute to vaccine protection, a systematic meta-analysis was conducted to evaluate efficacy data for vaccines in chickens challenged with highly pathogenic (HP) AI. Data from a total of 120 individual trials from 25 publications were selected and evaluated. Two vaccine criteria were evaluated for their effects on two metrics of protection. The vaccine criteria were: 1) the relatedness of the vaccine antigen and challenge strain in the hemagglutinin 1 domain (HA1) protein sequence; 2) vaccine-induced antibody titers to the challenge virus (VIAC). The metrics of protection were: A) survival of vaccinated chickens vs unvaccinated controls; and B) reduction in oral virus-shedding by vaccinated vs unvaccinated controls 2-4 days post challenge. Three vaccine platforms were evaluated: oil-adjuvanted inactivated whole AI virus, recombinant herpes virus of turkeys (rHVT) vectored, and a non-replicating alpha-virus vectored RNA particle (RP) vaccine. Higher VIAC correlated with greater reduction of virus-shed and vaccine efficacy by all vaccine platforms. Both higher HA1 relatedness and higher VIAC using challenge virus as antigen correlated with better survival by inactivated vaccines and rHVT-vectored vaccines. However, rHVT-vectored and RP based vaccines were more tolerant of variation in the HA1; the relatedness of the HA1 of the vaccine and challenge virus did not significantly correlate with survival with rHVT-vectored vaccines. Protection was achieved with the lowest aa similarity for which there was data, 90-93 % for rHVT vaccines and 88 % for the RP vaccine.

Chimeric H5 influenza virus-like particle vaccine elicits broader cross-clade antibody responses in chickens than in ducks

Eurasian-lineage highly pathogenic avian influenza (HPAI) H5 viruses have spread throughout Asia, the Middle East, Europe, Africa, and most recently, North and South America. These viruses are independently evolving into genetically and antigenically divergent clades, and broad-spectrum vaccines protecting against these divergent clades are needed. In this study, we developed a chimeric virus-like particle (VLP) vaccine co-expressing hemagglutinins from two clades (clades 1 and 2.3.2.1) of HPAI H5 viruses and performed comparative cross-clade hemagglutination inhibition (HI) analysis in chickens and ducks. The chimeric VLP immunization induced a significantly broader spectrum of antibodies against various clades of HPAI H5 viruses than monovalent VLPs both in chickens and ducks. While the chimeric VLP led to broadened antibody responses in both species, significantly lower levels of HI antibodies were elicited in ducks than in chickens. Moreover, boost immunization failed to increase antibody responses in ducks regardless of the VLPs used, in contrast to chickens that showed significantly enhanced antibody responses upon boost immunization. These results suggest (1) the potential application of the chimeric VLP technology in poultry to help control HPAI H5 viruses by offering broader antibody responses against antigenically different strains and (2) possible obstacles in generating high levels of antibody responses against HPAI H5 viruses in ducks via vaccination, implying the need for advanced vaccination strategies for ducks.

Recombinant hemagglutinin displaying on yeast reshapes congenital lymphocyte subsets to prompt optimized systemic immune protection against avian influenza infection

Introduction

Prophylactic vaccination is regarded as the most effective means to control avian flu infection. Currently, there is a need for a universal vaccine that provides broad and long-lasting protection against influenza virus. Meanwhile, although yeast-based vaccines have been used in clinic, studies are still required to further understand the molecular mechanism of yeast-based vaccines under physiological conditions.

Methods

We generated a yeast-based vaccine against influenza hemagglutinin (HA) of H5, H7 and H9 using surface displaying technology and evaluated the protective efficacy of chickens after exposure to H9N2 influenza virus.

Results

Oral yeast vaccine provided less clinical syndrome, reduced viral loading and alleviated airway damage significantly. Compared to the commercial inactivated vaccine, yeast vaccine stimulated the activation of splenic NK and APCs cells and boosted TLR7-IRF7-IFN signaling in spleen. Meanwhile, γδ T cells in the bursa of Fabricius were activated and the innate lymphoid cells (ILCs) in the bursa of Fabricius promoted the CILPs to differentiate to ILC3 cells in oral yeast birds. Moreover, the reshaped gut microbiota and a suppressed Th17-IL17-mediated inflammation in intestine was observed in oral yeast chickens, which might facilitate the recovery of intestinal mucosal immunity upon virus infection. Collectively, our findings suggest that oral yeast based multivalent bird flu vaccines provide an attractive strategy to update host defense function via reshapes of multi-systemic immune homeostasis.

Evaluation of three hemagglutinin-based vaccines for the experimental control of a panzootic clade 2.3.4.4b A(H5N8) high pathogenicity avian influenza virus in mule ducks

In France during winter 2016-2017, 487 outbreaks of clade 2.3.4.4b H5N8 subtype high pathogenicity (HP) avian influenza A virus (AIV) infections were detected in poultry and captive birds. During this epizootic, HPAIV A/decoy duck/France/161105a/2016 (H5N8) was isolated and characterized in an experimental infection transmission model in conventional mule ducks. To investigate options to possibly protect such ducks against this HPAIV, three vaccines were evaluated in controlled conditions. The first experimental vaccine was derived from the hemagglutinin gene of another clade 2.3.4.4b A(H5N8) HPAIV. It was injected at three weeks of age, either alone (Vac1) or after a primer injection at day-old (Vac1 + boost). The second vaccine (Vac2) was a commercial bivalent adjuvanted vaccine containing an expressed hemagglutinin modified from a clade 2.3.2 A(H5N1) HPAIV. Vac2 was administered as a single injection at two weeks of age. The third experimental vaccine (Vac3) also incorporated a homologous 2.3.4.4b H5 HA gene and was administered as a single injection at three weeks of age. Ducks were challenged with HPAIV A/decoy duck/France/161105a/2016 (H5N8) at six weeks of age. Post-challenge virus excretion was monitored in vaccinated and control birds every 2-3 days for two weeks using real-time reverse-transcription polymerase chain reaction and serological analyses (haemagglutination inhibition test against H5N8, H5 ELISA and AIV ELISA) were performed. Vac1 abolished oropharyngeal and cloacal shedding to almost undetectable levels, whereas Vac3 abolished cloacal shedding only (while partially reducing respiratory shedding) and Vac2 only partly reduced the respiratory and intestinal excretion of the challenge virus. These results provided relevant insights in the immunogenicity of recombinant H5 vaccines in mule ducks, a rarely investigated hybrid between Pekin and Muscovy duck species that has played a critical role in the recent H5 HPAI epizootics in France.

Protective Efficacy of H9N2 Avian Influenza Vaccines Inactivated by Ionizing Radiation Methods Administered by the Parenteral or Mucosal Routes

H9N2 viruses have become, over the last 20 years, one of the most diffused poultry pathogens and have reached a level of endemicity in several countries. Attempts to control the spread and reduce the circulation of H9N2 have relied mainly on vaccination in endemic countries. However, the high level of adaptation to poultry, testified by low minimum infectious doses, replication to high titers, and high transmissibility, has severely hampered the results of vaccination campaigns. Commercially available vaccines have demonstrated high efficacy in protecting against clinical disease, but variable results have also been observed in reducing the level of replication and viral shedding in domestic poultry species. Antigenic drift and increased chances of zoonotic infections are the results of incomplete protection offered by the currently available vaccines, of which the vast majority are based on formalin-inactivated whole virus antigens. In our work, we evaluated experimental vaccines based on an H9N2 virus, inactivated by irradiation treatment, in reducing viral shedding upon different challenge doses and compared their efficacy with formalin-inactivated vaccines. Moreover, we evaluated mucosal delivery of inactivated antigens as an alternative route to subcutaneous and intramuscular vaccination. The results showed complete protection and prevention of replication in subcutaneously vaccinated Specific Pathogen Free White Leghorn chickens at low-to-intermediate challenge doses but a limited reduction of shedding at a high challenge dose. Mucosally vaccinated chickens showed a more variable response to experimental infection at all tested challenge doses and the main effect of vaccination attained the reduction of infected birds in the early phase of infection. Concerning mucosal vaccination, the irradiated vaccine was the only one affording complete protection from infection at the lowest challenge dose. Vaccine formulations based on H9N2 inactivated by irradiation demonstrated a potential for better performances than vaccines based on the formalin-inactivated antigen in terms of reduction of shedding and prevention of infection.

Isolation of Genetically Diverse H5N8 Avian Influenza Viruses in Poultry in Egypt, 2019–2021

The global spread of avian influenza virus (AIV) of clade 2.3.4.4b since 2016 has caused severe losses in wild birds and poultry and has posed a risk for the infection of mammals including humans. The vaccination of poultry has been used to limit the spread of the virus and mitigate its socioeconomic impact. Here, we describe H5N8 epidemics in chickens, turkeys and ducks from different localities in Egypt from 2019 to 2021. About 41.7% (n = 88/211) flocks were tested positive by RT-qPCR for H5N8 viruses with prevalence rates of 45.1% (n = 65/144) and 34.3% (n = 23/67) in vaccinated and non-vaccinated flocks, respectively. A sequence analysis of the hemagglutinin and neuraminidase genes indicated not only the multiple introduction events of H5N8 viruses in Egypt but also the establishment of endemic viruses in commercial poultry in 2020/2021. The recent H5N8 viruses in poultry in Egypt are genetically distinct from the majority of licensed vaccines used in the field. Together, our findings indicate that poultry in Egypt is an endemic center for clade 2.3.4.4b in the Middle East. The efficiency of current vaccines should be regularly evaluated and updated to fully protect poultry flocks in Egypt against H5N8 viruses.

Has Epizootic Become Enzootic? Evidence for a Fundamental Change in the Infection Dynamics of Highly Pathogenic Avian Influenza in Europe, 2021

Phylogenetic evidence from the recent resurgence of high-pathogenicity avian influenza (HPAI) virus subtype H5N1, clade 2.3.4.4b, observed in European wild birds and poultry since October 2021, suggests at least two different and distinct reservoirs. We propose contrasting hypotheses for this emergence: (i) resident viruses have been maintained, presumably in wild birds, in northern Europe throughout the summer of 2021 to cause some of the outbreaks that are part of the most recent autumn/winter 2021 epizootic, or (ii) further virus variants were reintroduced by migratory birds, and these two sources of reintroduction have driven the HPAI resurgence. Viruses from these two principal sources can be distinguished by their hemagglutinin genes, which segregate into two distinct sublineages (termed B1 and B2) within clade 2.3.4.4b, as well as their different internal gene compositions. The evidence of enzootic HPAI virus circulation during the summer of 2021 indicates a possible paradigm shift in the epidemiology of HPAI in Europe.

Vaccines against Major Poultry Viral Diseases: Strategies to Improve the Breadth and Protective Efficacy

The poultry industry is the largest source of meat and eggs for human consumption worldwide. However, viral outbreaks in farmed stock are a common occurrence and a major source of concern for the industry. Mortality and morbidity resulting from an outbreak can cause significant economic losses with subsequent detrimental impacts on the global food supply chain. Mass vaccination is one of the main strategies for controlling and preventing viral infection in poultry. The development of broadly protective vaccines against avian viral diseases will alleviate selection pressure on field virus strains and simplify vaccination regimens for commercial farms with overall savings in husbandry costs. With the increasing number of emerging and re-emerging viral infectious diseases in the poultry industry, there is an urgent need to understand the strategies for broadening the protective efficacy of the vaccines against distinct viral strains. The current review provides an overview of viral vaccines and vaccination regimens available for common avian viral infections, and strategies for developing safer and more efficacious viral vaccines for poultry.

Live Recombinant NDV-Vectored H5 Vaccine Protects Chickens and Domestic Ducks From Lethal Infection of the Highly Pathogenic H5N6 Avian Influenza Virus

The H5 subtype highly pathogenic avian influenza virus (HPAIV) has been introduced to South Korea every 2 or 3 years via wild migratory waterfowls, causing devastating damages to the poultry industry. Although most damages and economic losses by HPAIV are focused on chicken layers, domestic ducks are known to play a major role in the farm-to-farm transmission. However, most HPAIV vaccine studies on poultry have been performed with oil-emulsion inactivated vaccines. In this study, we developed a live recombinant Newcastle disease virus (NDV)-vectored vaccine against H5 HPAIV (rK148/ES2-HA) using a previously established NDV vaccine strain (K148/08) isolated from a wild mallard duck. The efficacy of the vaccine when administered via the oculonasal route or as a spray was evaluated against lethal H5 HPAIV infection in domestic ducks and chickens. Oculonasal inoculation of the rK148/ES2-HA in chickens and ducks elicited antibody titers against HPAIV as early as 1 or 2 week after the single dose of vaccination, whereas spray vaccination in ducks elicited antibodies against HPAIV after the booster vaccination. The chickens and ducks vaccinated with rK148/ES2-HA showed high survival rates and low viral shedding after H5N6 HPAIV challenge. Collectively, vaccination with rK148/ES2-HA prevented lethal infection and decreased viral shedding in both chickens and ducks. The vaccine developed in this study could be useful in suppressing the viral shedding in H5 HPAIV outbreaks, with the ease of vaccine application and fast onset of immunity.

Molecular-based monitoring of live vaccines in dust samples from experimental and commercial chicken flocks and its potential use as a screening test

Despite the high cost of vaccination programmes, conventional methods to evaluate vaccine uptake are often impractical and costly. More recently, molecular-based testing of poultry dust has been used to monitor the "take" of Marek's disease virus and infectious laryngotracheitis virus (ILTV) live vaccines. This study aimed to provide proof-of-concept for detecting other poultry pathogens by using molecular detection of vaccine microorganisms in poultry dust of vaccinated flocks. Dust and choanal cleft and cloacal swabs were collected from chickens vaccinated against avian encephalomyelitis virus (AEV), fowlpox virus (FPV), Mycoplasma gallisepticum (MG) and Mycoplasma synoviae (MS) using live vaccines in an experimental flock. Dust samples were collected weekly from 5 commercial breeder or layer flocks from day-old up to 25 weeks of age. These flocks were vaccinated against Newcastle disease virus (NDV), infectious bronchitis virus (IBV), infectious bursal disease virus (IBDV), ILTV, fowl adenovirus (FAdV), MG and MS. Samples were tested for nucleic acids of these microorganisms by PCR or reverse transcriptase PCR. Genomes of all targeted vaccines were detected in dust samples from the experimental and commercial flocks except for FPV, which was detected only in the experimental flock. FAdV was detected in unvaccinated commercial flocks. These findings suggest that PCR detection of target organisms in dust samples has potential as a relatively simple and inexpensive population-level test to monitor vaccine take and/or pathogen status in chicken flocks. Further studies comparing the detection of each of these microorganisms in poultry dust with individual birds samples are required to validate this approach.

Protective Efficacy Evaluation of Four Inactivated Commercial Vaccines Against Low Pathogenic Avian Influenza H9N2 Virus Under Experimental Conditions in Broiler Chickens

Avian influenza vaccines are commonly used in the poultry industry. The objective of this study was to compare, under experimental conditions, the protective efficacy of four imported commercial inactivated H9N2 vaccines (A, B, C, and D) in broiler chickens. A total of 150 one-day-old chicks were divided into six groups: four experimental groups, each containing 30 chicks, received one of the vaccines (A, B, C, or D) delivered in a 0.3-ml dose subcutaneously at 1 day of age, whereas the control, Group T, was not vaccinated but challenged and Group E was kept unvaccinated and unchallenged. At 21 days postvaccination, Groups A, B, C, D, and T were challenged with 10⁷ embryo infective dose 50% of A/Chicken/Morocco/01/2016 (H9N2). All chicks were observed daily for clinical signs during the 12 days postchallenge (dpc). At 5 and 12 dpc, chicks were euthanatized for necropsy examination. Blood samples were collected weekly for serologic analysis and oropharyngeal swabs were collected for virus detection by real-time RT-PCR. Respiratory signs started at 48 hr pc and maximum severity was observed on 9 dpc. Chiefly, the birds vaccinated with vaccine B showed significantly more respiratory signs than did their counterparts. Serologic analysis revealed that the sera of Groups A and D birds showed a decrease in antibody (Ab) levels up to day 26; then a slight increase of Ab level was observed until day 31, while Group B and C birds showed a stabilization of the titers from day 21 until the end of the experiment. The viral shedding rate was significantly lower in Groups C and A (40%-50% of the birds shed virus for <7 days) compared with other challenged groups (60%-75% of the birds shed virus for ≥9 days). This experiment illustrated that vaccination applied on the first day in the hatchery with the four vaccines tested did not provide an acceptable protection against H9N2 in comparison with the controls that did not receive any vaccine. However, at first glance, we might favor vaccines A and C for their ability to reduce and shorten viral shedding as compared with vaccines B and D.

Antigenic evolution of contemporary clade 2.3.4.4 HPAI H5 influenza A viruses and impact on vaccine use for mitigation and control

Since 2003, highly pathogenic avian influenza (HPAI) viruses of the H5 subtype have been maintained in poultry, periodically spilling back into wild migratory birds and spread to other geographic regions, with re-introduction to domestic birds causing severe impacts for poultry health, production and food sustainability. Successive waves of infection have also resulted in substantial genetic evolution and reassortment, enabling the emergence of multiple clades and subtypes within the H5 2.3.4.4 HPAI viruses. Control of AI is principally through either culling or through vaccination using conventional vaccines. Here, we antigenically and genetically characterise the emerging 2020/21 H5NX clade 2.3.4.4 strains and assess cross-reactivity to putative vaccine strains using chicken antisera. We demonstrate significant antigenic differences between commercially available poultry vaccines and currently circulating viruses suggesting that vaccination options might be suboptimal in the current outbreaks.

Efficacy of two vaccines against recent emergent antigenic variants of clade 2.3.2.1a highly pathogenic avian influenza viruses in Bangladesh

H5N1 highly pathogenic avian influenza viruses (HPAIVs) have caused outbreaks in poultry in Bangladesh since 2007. While clade 2.2.2 and 2.3.4.2 HPAIVs have not been detected since 2012, clade 2.3.2.1a viruses have caused continuous outbreaks since 2012 despite the use of vaccines. In this study, we evaluated the efficacy of two H5 vaccines licensed in Bangladesh, RE-6 inactivated vaccine, and a recombinant herpesvirus of turkeys vaccine with an H5 insert (rHVT-H5), for protection against recent field viruses in chickens. We selected three viruses for efficacy tests (A/chicken/Bangladesh/NRL-AI-3237/2017, A/crow/Bangladesh/NRL-AI-8471/2017 and A/chicken/Bangladesh/NRL-AI-8323/2017) from 36 H5 viruses isolated from Bangladesh between 2016 and 2018 by comparing the amino acid sequences at five antigenic sites (A-E) and analyzing hemagglutination inhibition (HI) titers with reference antisera. The RE-6 and rHVT-H5 vaccines both conferred 80-100% clinical protection (i.e. reduced morbidity and mortality) against the three challenge viruses with no significant differences in protection. In addition, both vaccines significantly decreased viral shedding from infected chickens as compared to challenge control chickens. Based on these metrics, the current licensed H5 vaccines protected chickens against the recent field viruses. However, the A/crow/Bangladesh/NRL-AI-8471/2017 virus exhibited antigenic divergence including: several unique amino acid changes in antigenic epitope sites A and B and was a serological outlier in cross HI tests as visualized on the antigenic map. The continuing emergence of such antigenic variants which could alter the dominant antigenicity of field viruses should be continuously monitored and vaccines should be updated if field efficacy declines.

A broad spectrum HVT-H5 avian influenza vector vaccine which induces a rapid onset of immunity

Current methods to combat highly pathogenic avian influenza (HPAI) outbreaks in poultry rely on stamping out and preventive culling, which can lead to high economic losses and invoke ethical resistance. Emergency vaccination could be an alternative as vaccination is one of the most efficient and cost-effective measures to protect poultry from HPAI infection, preventing spreading to other poultry and greatly reducing the potential transmission to humans. Current conventional inactivated AI vaccines may be useful for combating AI outbreaks, but do not fulfil all targets of an ideal AI vaccine, including mass applicability and rapid onset of immunity. We aimed to further investigate the potential of Herpesvirus of Turkeys (HVT) as a vector containing a recombinant H5 hemagglutinin of HPAI H5N1. This HVT-H5 vector was analysed in vitro, tested for onset of immunity against AI challenge, breadth of protection, reduction of virus shedding, and induction of both antibody and cellular responses in SPF layers or broiler chicks containing maternal derived antibodies (MDA+). In SPF layers HVT-H5 provided full protection to lethal challenges with 4 antigenically diverse HPAI H5N1 strains from 2 weeks post vaccination (w.p.v.), while in MDA+ birds full protection was provided from 3 w.p.v. to homologous challenge. Also shedding of challenge virus was reduced in both SPF and MDA+ birds. HVT-H5 induced a protective HI titre (≥4) to 11 HPAI H5N1 strains at 3 w.p.v. in 3-week-old SPF layers and to HPAI H5N8 A/ch/Neth/14015531/2014. Besides inducing a protective antibody response HVT-H5 also induced an influenza-specific T cell response. This data demonstrates that HVT-H5 vaccine appears to fulfil many of the criteria for an ideal AI vaccine including early onset of immunity, a broad protection, reduced virus shedding, protection in presence of AI-MDA and could be a useful tool in the combat of AI outbreaks worldwide.

Evaluation of vaccination strategies to control an avian influenza outbreak in French poultry production networks using EVACS tool

France recently faced two epizootic waves of highly pathogenic avian influenza (HPAI) in poultry (H5N6 in 2015-2016 and H5N8 in 2016-2017), mainly in the fattening duck production sector. Vaccination against avian influenza (AI) is currently not authorised in France even though its potential benefits were discussed during these epizootic events. The objective of this work was to evaluate the potential efficiency of different vaccination strategies that could be applied against AI in France. The EVACS tool, which is a decision support tool developed to evaluate vaccination strategies, was applied in several French poultry production sectors: broiler, layer, turkey, duck and guinea fowl. EVACS was used to simulate the performance of vaccination strategies in terms of vaccination coverage, immunity levels and spatial distribution of the immunity level. A cost-benefit analysis was then applied based on EVACS results to identify the most efficient strategy. For each sector, vaccination protocols were tested according to the production type (breeders/production, indoor/outdoor), the integration level (integrated/independent) and the type of vaccine (hatchery vaccination using a recombinant vaccine/farm vaccination using an inactivated vaccine). The most efficient protocols for each sector were then combined to test different overall vaccination strategies at the national level. Even if it was not possible to compare vaccination protocols with the two vaccines types in "foie gras" duck, meat duck and guinea fowl production sectors as no hatchery vaccine currently exist for these species, these production sectors were also described and included in this simulation. Both types of vaccination (at hatchery and farm level) enabled protective immunity levels for the control of AI, but higher poultry population immunity level was reached (including independent farms) using hatchery vaccination. We also showed that hatchery vaccination was more efficient (higher benefit-cost ratio) than farm vaccination. Sufficient and homogeneously spatially distributed protective levels were reached in the overall poultry population with vaccination strategies targeting breeders, chicken layers and broilers and turkeys, without the need to include ducks and guinea fowls. However, vaccination strategies involving the highest number of species and production types were the most efficient in terms of cost-benefit. This study provides critical information on the efficiency of different vaccination strategies to support future decision making in case vaccination was applied to prevent and control HPAI in France.

Are current avian influenza vaccines a solution for smallholder poultry farmers?

Vaccination against highly pathogenic avian influenza (HPAI) viruses, along with other measures, was successful in eradicating AI in very few countries where the competence of national veterinary services or the geography and bird density have contributed favorably to the outcome.  The main constraints to an effective AI vaccination are vaccine composition matching field strains, reliable cold chain and logistics to target all poultry smallholders, constraints related to the availability of sufficient financial and human resources.  When not conducted properly, vaccination can also contribute to the emergence of new field viral strains, through genetic drifts of HPAI viruses.   While new technologies have improved the possibility to produce high quality vaccines matching field strains, recurrent issues like post-vaccination field surveillance and vaccination coverage continue to limit the relevance of AI vaccination in smallholder settings. A "game-changer" vaccine targeting smallholders should be universal to protect against all field viral strains and reduce significantly, if not totally eliminate, the need for costly post-vaccination surveillance.  The ease of administration of this vaccine (eye drop or one single injection) would further contribute to its relevance in the field.  These characteristics are considered essential for the product profile of an AI vaccine that can contribute in a meaningful way to the livelihoods of poultry smallholders.

Genetic evolution and transmission dynamics of clade 2.3.2.1a highly pathogenic avian influenza A/H5N1 viruses in Bangladesh

Asian lineage A/H5N1 highly pathogenic avian influenza viruses (HPAIVs) have been responsible for continuous outbreaks in Bangladesh since 2007. Although clades 2.2.2 and 2.3.4.2 HPAIVs have disappeared since poultry vaccination was introduced in 2012, clade 2.3.2.1a viruses have continued to be detected in Bangladesh. In this study, we identified A/H9N2 (n = 15), A/H5N1 (n = 19), and A/H5N1-A/H9N2 (n = 18) mixed viruses from live bird markets, chicken farms, and wild house crows (Corvus splendens) in Bangladesh from 2016 to 2018. We analyzed the genetic sequences of the H5 HPAIVs, to better understand the evolutionary history of clade 2.3.2.1a viruses in Bangladesh. Although seven HA genetic subgroups (B1-B7) and six genotypes (G1, G1.1, G1.2, G2, G2.1, and G2.2) have been identified in Bangladesh, only subgroup B7 and genotypes G2, G2.1, and G2.2 were detected after 2016. The replacement of G1 genotype by G2 in Bangladesh was possibly due to vaccination and viral competition in duck populations. Initially, genetic diversity decreased after introduction of vaccination in 2012, but in 2015, genetic diversity increased and was associated with the emergence of genotype G2. Our phylodynamic analysis suggests that domestic Anseriformes, including ducks and geese, may have played a major role in persistence, spread, evolution, and genotype replacement of clade 2.3.2.1a HPAIVs in Bangladesh. Thus, improvements in biosecurity and monitoring of domestic Anseriformes are needed for more effective control of HPAI in Bangladesh.

Efficacy of a plant-produced virus-like particle vaccine in chickens challenged with Influenza A H6N2 virus

The efficacy, safety, speed, scalability and cost-effectiveness of producing hemagglutinin-based virus-like particle (VLP) vaccines in plants are well-established for human influenza, but untested for the massive poultry influenza vaccine market that remains dominated by traditional egg-grown oil-emulsion whole inactivated virus vaccines. For optimal efficacy, a vaccine should be closely antigenically matched to the field strain, requiring that influenza A vaccines be updated regularly. In this study, an H6 subtype VLP transiently expressed in Nicotiana benthamiana was formulated into a vaccine and evaluated for efficacy in chickens against challenge with a heterologous H6N2 virus. A single dose of the plant-produced H6 VLP vaccine elicited an immune response comparable to two doses of a commercial inactivated H6N2 vaccine, with mean hemagglutination inhibition titres of 9.3 log2 and 8.8 log2 , respectively. Compared to the non-vaccinated control, the H6 VLP vaccine significantly reduced the proportion of shedders and the magnitude of viral shedding by >100-fold in the oropharynx and >6-fold in the cloaca, and shortened oropharyngeal viral shedding by at least a week. Despite its potency, the cost of the antigenic mismatch between the inactivated H6N2 vaccine and challenge strain was evident not only in this vaccine's failure to reduce viral shedding compared to the non-vaccinated group, but its apparent exacerbation of oropharyngeal viral shedding until 21 days post-challenge. We estimate that a kilogram of plant leaf material can produce H6 VLP vaccines sufficient for between 5000 and 30 000 chickens, depending on the effective dose and whether one or two immunizations are administered.

Protective efficacy of vaccines of the Korea national antigen bank against the homologous H5Nx clade 2.3.2.1 and clade 2.3.4.4 highly pathogenic avian influenza viruses

The occurrence of severe outbreaks of highly pathogenic avian influenza in Korea led to establishment of a national antigen bank for emergency preparedness. Here, we developed five vaccines for this bank (clade 2.3.2.1C, clade 2.3.4.4A, B, C, and D) by reverse genetics, inactivated them with formalin, and evaluated the protective efficacy and potency of serial dilutions against lethal homologous challenge in specific-pathogen-free chickens. After vaccination with one dose, each vaccine resulted in 100% survival, with no clinical symptoms, or lack of detectable virus shedding, and high levels of pre-challenge protective immunity (8.4-10.2 log₂). After vaccination with one-tenth of the full dose, protection was similar to that with the full dose. After vaccination with one-hundredth of the initial dose, survival was 20-80%, and all vaccines showed virus shedding. Four vaccines (excluding clade 2.3.2.1C) had satisfactory potency. In antibody-persistence tests, all vaccines maintained long-lasting protective immunity. Our results suggest that inactivated reverse-genetics vaccines genetically matched to outbreak viruses provide adequate protection after a single vaccination.

Protective immunity against influenza virus challenge by norovirus P particle-M2e and HA2-AtCYN vaccines in chickens

Development of a broadly reactive influenza vaccine that can provide protection against emerging type A influenza viruses is a big challenge. We previously demonstrated that a vaccine displaying the extracellular domain of the matrix protein 2 (M2e) on the surface loops of norovirus P-particle (M2eP) can partially protect chickens against several subtypes of avian influenza viruses. In the current study, a chimeric vaccine containing a conserved peptide from the subunit 2 of hemagglutinin (HA) glycoprotein (HA2) and Arabidopsis thaliana cyanase protein (AtCYN) (HA2-AtCYN vaccine) was evaluated in 2-weeks-old chickens. Depending on the route of administration, the HA2-AtCYN vaccine was shown to induce various levels of HA2-specific IgA in tears as well as serum IgG, which were associated with partial protection of chickens against tracheal shedding of a low pathogenicity H5N2 challenge virus. Furthermore, intranasal administration with a combination of HA2-AtCYN and M2eP vaccines resulted in enhanced protection compared to each vaccine alone. Simultaneous intranasal administration of the vaccines did not interfere with secretory IgA induction by each vaccine. Additionally, significantly higher M2eP-specific proliferative responses were observed in peripheral blood mononuclear cells of all M2eP-vaccinated groups when compared with the mock-vaccinated group. Although tripling the number of M2e copies did not enhance the protective efficacy of the chimeric vaccine, it significantly reduced immunodominance of P-particle epitopes without affecting the robustness of M2e-specific immune responses. Taken together, our data suggests that mucosal immunization of chickens with combinations of mechanistically different cross-subtype-conserved vaccines has the potential to enhance the protective efficacy against influenza virus challenge.

Protective efficacy of an inactivated chimeric H5 avian influenza vaccine against H5 highly pathogenic avian influenza virus clades 2.3.4.4 and 2.3.2.1

The H5 subtype of highly pathogenic avian influenza (HPAI) viruses pose a serious challenge to public health and the poultry industry in China. In this study, we generated a chimeric QH/KJ recombinant virus expressing the entire haemagglutinin (HA)-1 region of the HPAI virus A/chicken/China/QH/2017(H5N6) (clade 2.3.4.4) and the HA2 region of the HPAI virus A/chicken/China/KJ/2017(H5N1) (clade 2.3.2.1). The resulting chimeric PR8-QH/KJ virus exhibited similar in vitro growth kinetics as the parental PR8-QH and PR8-KJ viruses. The chimeric PR8-QH/KJ virus induced specific, cross-reactive haemagglutination-inhibition and serum-neutralizing antibodies against both QH and KJ viruses, although PR8-QH and PR8-KJ exhibited no cross-reactivity with each other. Furthermore, the chimeric PR8-QH/KJ vaccine significantly reduced virus shedding and completely protected chickens from challenge with HPAI H5N6 and H5N1 viruses. However, the Re-8 vaccine against clade 2.3.4.4 viruses provided specific-pathogen-free chickens only partial protection when challenged with QH virus. Our results suggest that the antigenic variation of these epidemic viruses occurred and they can escape the current vaccine immunization. The Re-8 vaccine needs an update. The chimeric PR8-QH/KJ vaccine is effective against H5 HPAI virus clades 2.3.4.4 and 2.3.2.1 in chickens.

Maternal antibody inhibition of recombinant Newcastle disease virus vectored vaccine in a primary or booster avian influenza vaccination program of broiler chickens

Maternally-derived antibodies (MDA) provide early protection from disease, but may interfere with active immunity in young chicks. In highly pathogenic avian influenza virus (HPAIV)-enzootic countries, broiler chickens typically have MDA to Newcastle disease virus (NDV) and H5 HPAIV, and their impact on active immunity from recombinant vectored vaccines is unclear. We assessed the effectiveness of a spray-applied recombinant NDV vaccine with H5 AIV insert (rNDV-H5) and a recombinant turkey herpesvirus (HVT) vaccine with H5 AIV insert (rHVT-H5) in commercial broilers with MDA to NDV alone (MDA:AIV^-NDV⁺) or to NDV plus AIV (MDA:AIV⁺NDV⁺) to provide protection against homologous HPAIV challenge. In Experiment 1, chicks were spray-vaccinated with rNDV-H5 at 3 weeks (3w) and challenged at 5 weeks (5w). All sham-vaccinated progeny lacked AIV antibodies and died following challenge. In rNDV-H5 vaccine groups, AIV and NDV MDA had completely declined to non-detectable levels by vaccination, enabling rNDV-H5 spray vaccine to elicit a protective AIV antibody response by 5w, with 70-78% survival and significant reduction of virus shedding compared to shams. In Experiment 2, progeny were vaccinated with rHVT-H5 and rNDV-H5 at 1 day (1d) or 3w and challenged at 5w. All sham-vaccinated progeny lacked AIV antibodies and died following challenge. In rHVT-H5(1d) vaccine groups, irrespective of rNDV-H5(3w) boost, AIV antibodies reached protective levels pre-challenge, as all progeny survived and virus shedding significantly decreased compared to shams. In contrast, rNDV-H5-vaccinated progeny had AIV and/or NDV MDA at the time of vaccination (1d and/or 3w) and failed to develop a protective immune response by 5w, resulting in 100% mortality after challenge. Our results demonstrate that MDA to AIV had minimal impact on the effectiveness of rHVT-H5, but MDA to AIV and/or NDV at the time of vaccination can prevent development of protective immunity from a primary or booster rNDV-H5 vaccine.

Protective efficacy of an inactivated chimeric H7/H5 avian influenza vaccine against highly pathogenic avian influenza H7N9 and clade 2.3.4.4 H5 viruses

The highly pathogenic avian influenza (HPAI) H5 and H7N9 viruses pose a serious challenge to public health and the poultry industry in China. In this study, we generated a chimeric H7/H5 recombinant virus that expressed the entire HA1 region of the HPAI A/chicken/Guangdong/RZ/2017(H7N9) virus and the HA2 region of the HPAI A/chicken/Fujian/5/2016(H5N6) viruses. The resulting chimeric PR8-H7/H5 virus exhibited similar growth kinetics as the parental PR8-H5 and PR8-H7 viruses in vitro. The inactivated chimeric PR8-H7/H5 vaccine induced specific, cross-reactive hemagglutination inhibition antibodies against the H7 virus only but induced serum-neutralizing antibodies against both H7 and H5 viruses. Furthermore, the inactivated chimeric PR8-H7/H5 vaccine significantly reduced virus shedding and protected chickens from challenge with the HPAI H5N6 and H7N9 viruses. Our results suggested that the inactivated chimeric PR8-H7/H5 vaccine was effective against HPAI H5 and H7N9 viruses in chickens.

Influenza viral vectors expressing two kinds of HA proteins for bivalent vaccines against clade 2.3.4.4 and clade 2.3.2.1 H5 HPAIVs

The H5 highly pathogenic avian influenza viruses (HPAIVs) in China pose a serious challenge to public health and the poultry industry. In this study, we constructed a replication-competent recombinant influenza A virus of clade 2.3.4.4 Н5N1 expressing the clade 2.3.2.1 H5 HA1 protein from a tricistronic NS segment. We used a truncated NS1 protein of 73 amino acids combined with a heterologous dimerization domain to increase protein stability. H5 HA1 and nuclear export information were fused in frame with a truncated NS1 open reading frame, separated by 2A self-processing sites. The resulting PR8-H5-NS1(73)H5 stably expressed clade 2.3.4.4 H5 HA and clade 2.3.2.1 H5 HA1 proteins and exhibited similar in vitro growth kinetics as the parental PR8-2344H5 virus. PR8-H5-NS1(73)H5 induced specific hemagglutination-inhibition (HI) antibody against clade 2.3.4.4 H5 that was comparable to that of the combination vaccine of PR8-2344H5 and PR8-2321H5. HI antibody titers were significantly lower against clade 2.3.2.1 H5 virus than with the combination vaccine. PR8-H5-NS1(73)H5 completely protected chickens from both clade 2.3.4.4 and clade 2.3.2.1 H5 HPAIVs challenge. Our results suggested that PR8-H5-NS1(73)H5 was highly immunogenic and efficacious against both clade 2.3.4.4 and clade 2.3.2.1 H5 HPAIVs in chickens.

Influenza Viral Vectors Expressing Two Kinds of HA Proteins as Bivalent Vaccine Against Highly Pathogenic Avian Influenza Viruses of Clade 2.3.4.4 H5 and H7N9

The H5 and H7N9 subtypes of highly pathogenic avian influenza viruses (HPAIVs) in China pose a serious challenge to public health and the poultry industry. In this study, a replication competent recombinant influenza A virus of the Í5N1 subtype expressing the H7 HA1 protein from a tri-cistronic NS segment was constructed. A heterologous dimerization domain was used to combine with the truncated NS1 protein of 73 amino acids to increase protein stability. H7 HA1, nuclear export protein coding region, and the truncated NS1 were fused in-frame into a single open reading frame via 2A self-cleaving peptides. The resulting PR8-H5-NS1(73)H7 stably expressed the H5 HA and H7 HA1 proteins, and exhibited similar growth kinetics as the parental PR8-H5 virus in vitro. PR8-H5-NS1(73)H7 induced specific hemagglutination inhibition (HI) antibody against H5, which was comparable to that of the combination vaccine of PR8-H5 and PR8-H7. The HI antibody titers against H7 virus were significantly lower than that by the combination vaccine. PR8-H5-NS1(73)H7 completely protected chickens from challenge with both H5 and H7 HPAIVs. These results suggest that PR8-H5-NS1(73)H7 is highly immunogenic and efficacious against both H5 and H7N9 HPAIVs in chickens.

Highlights:

- PR8-H5-NS1(73)H7 simultaneously expressed two HA proteins of different avian influenza virus subtypes.

- PR8-H5-NS1(73)H7 was highly immunogenic in chickens.

- PR8-H5-NS1(73)H7 provided complete protection against challenge with both H5 and H7N9 HPAIVs.

Immunization of Domestic Ducks with Live Nonpathogenic H5N3 Influenza Virus Prevents Shedding and Transmission of Highly Pathogenic H5N1 Virus to Chickens

Wild ducks are known to be able to carry avian influenza viruses over long distances and infect domestic ducks, which in their turn infect domestic chickens. Therefore, prevention of virus transmission between ducks and chickens is important to control the spread of avian influenza. Here we used a low pathogenic wild aquatic bird virus A/duck/Moscow/4182/2010 (H5N3) for prevention of highly pathogenic avian influenza virus (HPAIV) transmission between ducks and chickens. We first confirmed that the ducks orally infected with H5N1 HPAIV A/chicken/Kurgan/3/2005 excreted the virus in feces. All chickens that were in contact with the infected ducks became sick, excreted the virus, and died. However, the ducks orally inoculated with 10⁴ 50% tissue culture infective doses of A/duck/Moscow/4182/2010 and challenged 14 to 90 days later with H5N1 HPAIV did not excrete the challenge virus. All contact chickens survived and did not excrete the virus. Our results suggest that low pathogenic virus of wild aquatic birds can be used for prevention of transmission of H5N1 viruses between ducks and chickens.

A two dose immunization with an inactivated reassortant H5N2 virus protects chickens against lethal challenge with homologous 2.3.2.1 clade and heterologous 2.2 clade highly pathogenic avian influenza H5N1 viruses

The present study was aimed at generating a reassortant vaccine candidate virus with clade 2.3.2.1 Hemagglutinin (HA) and its evaluation in a challenge study for protection against homologous (2.3.2.1 clade) and heterologous (2.2 clade) highly pathogenic avian influenza (HPAI) H5N1 viruses. Plasmid-based reverse genetics technique was used to rescue a 5 + 3 reassortant H5N2 strain containing the modified HA of H5N1 (clade 2.3.2.1), the Neuraminidase (NA) of H9N2, the Matrix (M) of H5N1 and the internal genes of A/WSN/33 H1N1. In addition, another 6 + 2 reassortant virus containing modified HA from H5N1 (clade 2.3.2.1), the NA from H9N2 and the internal genes of A/WSN/33 H1N1 was also rescued. The 5 + 3 reassortant H5N2 virus could grow to a higher titer in both MDCK cells and chicken eggs compared to the 6 + 2 reassortant H5N2 virus. The vaccine containing the inactivated 5 + 3 reassortant H5N2 virus was used in a two-dose immunization regime which protected specific pathogen free (SPF) chickens against two repeated challenges with homologous 2.3.2.1 clade and heterologous 2.2 clade HPAI H5N1 viruses. The 5 + 3 reassortant H5N2 virus based on clade 2.3.2.1 generated in this study can be effective in protecting chickens in the case of an outbreak caused by antigenically different clade 2.2 HPAI H5N1 viruses and opens the way to explore its applicability as potential vaccine candidate especially in the Asian countries reporting these clades frequently. The study also indicates that sequential immunization can broaden protection level against antigenically diverse strains of H5N1 viruses.

Challenge for One Health: Co-Circulation of Zoonotic H5N1 and H9N2 Avian Influenza Viruses in Egypt

Highly pathogenic avian influenza (HPAI) H5N1 viruses are currently endemic in poultry in Egypt. Eradication of the viruses has been unsuccessful due to improper application of vaccine-based control strategies among other preventive measures. The viruses have evolved rapidly with increased bird-to-human transmission efficacy, thus affecting both animal and public health. Subsequent spread of potentially zoonotic low pathogenic avian influenza (LPAI) H9N2 in poultry has also hindered efficient control of avian influenza. The H5N1 viruses acquired enhanced bird-to-human transmissibility by (1) altering amino acids in hemagglutinin (HA) that enable binding affinity to human-type receptors, (2) loss of the glycosylation site and 130 loop in the HA protein and (3) mutation of E627K in the PB2 protein to enhance viral replication in mammalian hosts. The receptor binding site of HA of Egyptian H9N2 viruses has been shown to contain the Q234L substitution along with a H191 mutation, which can increase human-like receptor specificity. Therefore, co-circulation of H5N1 and H9N2 viruses in poultry farming and live bird markets has increased the risk of human exposure, resulting in complication of the epidemiological situation and raising a concern for potential emergence of a new influenza A virus pandemic. For efficient control of infection and transmission, the efficacy of vaccine and vaccination needs to be improved with a comprehensive control strategy, including enhanced biosecurity, education, surveillance, rapid diagnosis and culling of infected poultry.

Intranasal administration of inactivated avian influenza virus of H5N1 subtype vaccine-induced systemic immune response in chicken and mice

Aim

The need for non-parenteral administration of inactivated avian influenza virus of H5N1 subtype (AIV-H5N1) vaccine is paramount. Here, we provide preliminary data on the immune response of chicken and mice after intranasal administration of AIV-H5N1-inactivated vaccine with ISCOMS, Inmunair (INM), and combined ISCOMS and INM as an adjuvant.

Materials and Methods

The AIV isolate of A/Chicken/Denpasar/01/2004 (H5N1) was cultivated in specific pathogen-free chicken eggs and inactivated with formaldehyde. The vaccine preparation was added with those adjuvants for intranasal administration and aluminum hydroxide for subcutaneous injection. The chicken and mouse were vaccinated at the age of 3 weeks or 1 month and repeated 2 weeks thereafter. In one experiment, chicken was injected with Newcastle disease virus (NDV) at the same time with AIV vaccine. The sera were collected at one (serum 1) and 2 w (serum 2) after booster vaccination. The anti-AIV-H5 and NDV antibodies in chicken sera were detected using hemagglutination inhibition (HI) assay. Mouse IgG anti-AIV-H5N1 antibody was detected using ELISA.

Results

The result shows that the geometric mean titers (GMTs) of chicken sera of intranasal vaccinated with inactivated AIV-H5N1 vaccine with mixed ISCOM- INM as adjuvant were <2^0.0 and 2^2.7 unit HI-unit (HIU) in serum 1 and serum 2, respectively. The GMTs of the positive control group were 2^3.7 and 2^5.7 HIU in serum 1 and serum 2, respectively. The result of the second experiment shows that IgG anti-AIV-H5N1 was detected in mouse sera. In the third experiment, the GMTs of anti-NDV in chicken vaccinated subsequently with inactivated NDV vaccine and AIV-H5N1 with mixed ISCOMS-INM administrated intranasally and aluminum hydroxide adjuvant administrated through subcutaneous injection as well as positive control group receiving NDV vaccine only were 2^8.0, 2^8.0, and 2^7.4 HIU in serum 1 while were 2^9.6, 2^9.2, and 2^8.2 HIU in serum 2, respectively.

Conclusion

Intranasal administration of inactivated AIV-H5N1 vaccine-induced a systemic immune response in chicken and mice after adding ISCOMS and/or INM as adjuvants. The adjuvant and the intranasal administration caused no immunosuppressive effect on the chicken immune response to NDV vaccine.

Protection of commercial turkeys following inactivated or recombinant H5 vaccine application against the 2015U.S. H5N2 clade 2.3.4.4 highly pathogenic avian influenza virus

Between December 2014 and June 2015, North America experienced the largest recorded foreign animal disease outbreak with over 47 million poultry dead or euthanized from viral exposure to a clade 2.3.4.4 H5 highly pathogenic avian influenza (HPAI) epizootic. Soon after the epizootic began, the U.S. Department of Agriculture (USDA) began testing the efficacy of different vaccines as a possible future control strategy. The aim of these studies were to evaluate the efficacy three H5 vaccines to aid in control of HPAI in commercial turkeys. Three different vaccine technologies were evaluated for efficacy: 1) inactivated reverse genetic laboratory-generated virus encoding a clade 2.3.4.4 H5 hemagglutinin (HA) gene (rgH5), 2) recombinant turkey herpesvirus encoding a clade 2.2. H5 HA (rHVT-AI), and 3) recombinant replication-deficient alphavirus RNA particle vaccine encoding a clade 2.3.4.4 H5 HA (RP-H5). All vaccines tested significantly (P<0.01) increased survival rates between vaccinated and sham vaccinated groups of poults challenged with A/turkey/Minnesota/12582/2015 clade 2.3.4.4 H5N2 HPAI. The rgH5 vaccine had detectable serum hemagglutination inhibition (HI) antibody against the challenge virus, and significantly reduced the frequency and level of viral shedding from oropharyngeal and cloacal swabs at days 2 and 4 post-challenge. Vaccination with only rHVT-AI or RP-H5 was not 100% protective, and failed to significantly reduce viral shedding post-challenge. A combined prime and boost strategy with the rHVT-AI and RP-H5, or rHVT-AI and rgH5, was 100% protective against lethal H5N2 HPAI challenge. Results of these studies led to USDA conditional approval of commercially available recombinant vaccines for use in turkeys as a control measure for clade 2.3.4.4 H5 HPAI epizootics.

Protection Afforded by a Recombinant Turkey Herpesvirus-H5 Vaccine Against the 2014 European Highly Pathogenic H5N8 Avian Influenza Strain

A highly pathogenic avian influenza (HPAI) H5N8 (clade 2.3.4.4) virus, circulating in Asia (South Korea, Japan, and southern China) since the beginning of 2014, reached the European continent in November 2014. Germany, the Netherlands, the United Kingdom, Italy, and Hungary confirmed H5N8 infection of poultry farms of different species and of several wild bird species. Unlike the Asian highly pathogenic (HP) H5N1, this HP H5N8 also went transatlantic and reached the American West Coast by the end of 2014, affecting wild birds as well as backyard and commercial poultry. This strain induces high mortality and morbidity in Galliformes, whereas wild birds seem only moderately affected. A recombinant turkey herpesvirus (rHVT) vector vaccine expressing the H5 gene of a clade 2.2 H5N1 strain (rHVT-H5) previously demonstrated a highly efficient clinical protection and reduced viral excretion against challenge with Asian HP H5N1 strains of various clades (2.2, 2.2.1, 2.2.1.1, 2.1.3, 2.1.3.2, and 2.3.2.1) and was made commercially available in various countries where the disease is endemic. To evaluate the protective efficacy of the rHVT-H5 vaccine against the first German H5N8 turkey isolate (H5N8 GE), a challenge experiment was set up in specific-pathogen-free (SPF) chickens, and the clinical and excretional protection was evaluated. SPF chickens were vaccinated subcutaneously at 1 day old and challenged oculonasally at 4 wk of age with two viral dosages, 10(5) and 10(6) 50% egg infective doses. Morbidity and mortality were monitored daily in unvaccinated and vaccinated groups, whereas viral shedding by oropharyngeal and cloacal routes was evaluated at 2, 5, 9, and 14 days postinoculation (dpi). Serologic monitoring after vaccination and challenge was also carried out. Despite its high antigenic divergence of the challenge H5N8 strain, a single rHVT-H5 vaccine administration at 1 day old resulted in a full clinical protection against challenge and a significant reduction of viral shedding in the vaccinated birds.

Protective Efficacy of the Inactivated H5N1 Influenza Vaccine Re-6 Against Different Clades of H5N1 Viruses Isolated in China and the Democratic People's Republic of Korea

An inactivated H5N1 avian influenza (AI) vaccine (Re-6) that bears the HA and NA genes from a clade 2.3.2.1 H5N1 virus, A/duck/Guangdong/S1322/10 (DK/GD/S1322/10), has been used in domestic poultry in China and other Southeast Asian countries to control clade 2.3.2.1 H5N1viruses since 2012. The efficacy of this vaccine against H5N1 viruses isolated in recent years has not been reported. In this study, we evaluated the protection efficacy of the Re-6 vaccine in chickens against challenge with four clade 2.3.2.1 H5N1 viruses, one clade 2.3.4.4 H5N1 virus, and one clade 7.2 H5N1 virus; these viruses were isolated in mainland China, Hong Kong, and the Democratic People's Republic of Korea between 2011 and 2015. The vaccinated chickens were completely protected (no disease signs, virus shedding, or death) from the challenge with the four clade 2.3.2.1 H5N1 viruses. In the clade 7.2 virus-challenged group, all of the vaccinated chickens remained healthy and survived for the entire 2-wk observation period; virus shedding was only detected from 1 of 10 chickens on day 3 postchallenge. In the clade 2.3.4.4 virus-challenged group, 8 of the 10 vaccinated chickens remained healthy and survived the 2-wk observation period; however, virus shedding was detected from 8 of 10 chickens on day 5 postchallenge. These results indicate that the Re-6 vaccine provides solid protection against clade 2.3.2.1, good protection against clade 7.2, and poor protection against clade 2.3.4.4.

Newcastle disease virus vectored vaccines as bivalent or antigen delivery vaccines

Recent advances in reverse genetics techniques make it possible to manipulate the genome of RNA viruses such as Newcastle disease virus (NDV). Several NDV vaccine strains have been used as vaccine vectors in poultry, mammals, and humans to express antigens of different pathogens. The safety, immunogenicity, and protective efficacy of these NDV-vectored vaccines have been evaluated in pre-clinical and clinical studies. The vaccines are safe in mammals, humans, and poultry. Bivalent NDV-vectored vaccines against pathogens of economic importance to the poultry industry have been developed. These bivalent vaccines confer solid protective immunity against NDV and other foreign antigens. In most cases, NDV-vectored vaccines induce strong local and systemic immune responses against the target foreign antigen. This review summarizes the development of NDV-vectored vaccines and their potential use as a base for designing other effective vaccines for veterinary and human use.

Protection of White Leghorn chickens by U.S. emergency H5 vaccination against clade 2.3.4.4 H5N2 high pathogenicity avian influenza virus

During December 2014-June 2015, the U.S. experienced a high pathogenicity avian influenza (HPAI) outbreak caused by clade 2.3.4.4 H5Nx Goose/Guangdong lineage viruses with devastating consequences for the poultry industry. Three vaccines, developed based on updating existing registered vaccines or currently licensed technologies, were evaluated for possible use: an inactivated reverse genetics H5N1 vaccine (rgH5N1) and an RNA particle vaccine (RP-H5), both containing the hemagglutinin gene of clade 2.3.4.4 strain, and a recombinant herpesvirus turkey vectored vaccine (rHVT-H5) containing the hemagglutinin gene of clade 2.2 strain. The efficacy of the three vaccines, alone or in combination, was assessed in White Leghorn chickens against clade 2.3.4.4 H5N2 HPAI virus challenge. In Study 1, single (rHVT-H5) and prime-boost (rHVT-H5+rgH5N1 or rHVT-H5+RP-H5) vaccination strategies protected chickens with high levels of protective immunity and significantly reduced virus shedding. In Study 2, single vaccination with either rgH5N1 or RP-H5 vaccines provided clinical protection in adult chickens and significantly reduced virus shedding. In Study 3, double rgH5N1 vaccination protected adult chickens from clinical signs and mortality when challenged 20weeks post-boost, with high levels of long-lasting protective immunity and significantly reduced virus shedding. These studies support the use of genetically related vaccines, possibly in combination with a broad protective priming vaccine, for emergency vaccination programs against clade 2.3.4.4 H5Nx HPAI virus in young and adult layer chickens.

Swine and Avian Influenza Outbreaks in Recent Times

Influenza A is a zoonotic virus and wild waterfowls are the main reservoir of avian influenza viruses, which are precursors of human influenza A viruses. Through mutations and gene reassortment, some strains of avian influenza viruses establish stable lineages in poultry species, pigs, horses, and humans. The first zoonotic influenza pandemic of the twenty-first century, the swine H1N1 pandemic of 2009, originated from Mexico, and fortunately the virus was only of modest virulence. However, lessons have been learned on the shortcomings of the global preparedness for influenza pandemic, and this should be considered as a valuable experience for the preparation of the next major outbreak. Of more concern is the emergence of the highly pathogenic avian influenza A [H5N1], ongoing since 1996, and the low pathogenic avian influenza A [H7N9], since 2013, which have crossed the species barrier to humans in China. Risks of a H5N1 pandemic appear to be receding with declining human cases, and the H7N9 influenza virus is now the leading candidate as the next pandemic influenza virus. However, influenza pandemics are unpredictable in their timing, specific strain of virus, and origin. Most experts predict that the next influenza pandemic will arise from Asia, especially China, and will be directly of avian origin. Continued influenza surveillance in animals and humans globally with prompt reporting to the WHO and the World Animal Health Organization with sharing of data promptly between countries is essential. Long-term solutions to prevent cross-species transmission of zoonotic influenza viruses to humans and development of more effective, longer-lasting vaccines against emerging avian influenza viruses are needed. Currently there is no evidence of an impending zoonotic or avian influenza pandemic, and the viruses of interest, H5N1 and H7N9 avian influenza A viruses, have not mutated to allow for easy transmission to humans nor human to human.

Presence of Vaccine-Derived Newcastle Disease Viruses in Wild Birds

Our study demonstrates the repeated isolation of vaccine-derived Newcastle disease viruses from different species of wild birds across four continents from 1997 through 2014. The data indicate that at least 17 species from ten avian orders occupying different habitats excrete vaccine-derived Newcastle disease viruses. The most frequently reported isolates were detected among individuals in the order Columbiformes (n = 23), followed in frequency by the order Anseriformes (n = 13). Samples were isolated from both free-ranging (n = 47) and wild birds kept in captivity (n = 7). The number of recovered vaccine-derived viruses corresponded with the most widely utilized vaccines, LaSota (n = 28) and Hitchner B1 (n = 19). Other detected vaccine-derived viruses resembled the PHY-LMV2 and V4 vaccines, with five and two cases, respectively. These results and the ubiquitous and synanthropic nature of wild pigeons highlight their potential role as indicator species for the presence of Newcastle disease virus of low virulence in the environment. The reverse spillover of live agents from domestic animals to wildlife as a result of the expansion of livestock industries employing massive amounts of live virus vaccines represent an underappreciated and poorly studied effect of human activity on wildlife.

Impacts of poultry vaccination on viruses of wild bird

Spillover of viruses from farmed poultry into wild birds is a relatively new area of study at the livestock-wildlife interface. These transmission events can threaten the health of wild birds. There is growing evidence of transmission of vaccine viruses from poultry to wild birds, including attenuated vaccine strains of Newcastle disease virus and infectious bronchitis virus, and also spread of virulent viruses that may have evolved under the pressure of vaccine use, such as Marek's disease virus. Viral contaminants of poultry vaccines, including reticuloendotheliosis virus, may also be transmitted to wild birds and result in disease. New, vectored vaccines are less likely to directly spread to wild birds but this risk may rise as a result of recombination.