Haemagglutinin and nucleoprotein replicon particle vaccination of swine protects against the pandemic H1N1 2009 virus

Detection and Characterization of Influenza A Virus Endemic Circulation in Suckling and Nursery Pigs Originating from Vaccinated Farms in the Same Production System

Inactivated influenza A virus (IAV) vaccines help reduce clinical disease in suckling piglets, although endemic infections still exist. The objective of this study was to evaluate the detection of IAV in suckling and nursery piglets from IAV-vaccinated sows from farms with endemic IAV infections. Eight nasal swab collections were obtained from 135 two-week-old suckling piglets from four farms every other week from March to September 2013. Oral fluid samples were collected from the same group of nursery piglets. IAV RNA was detected in 1.64% and 31.01% of individual nasal swabs and oral fluids, respectively. H1N2 was detected most often, with sporadic detection of H1N1 and H3N2. Whole-genome sequences of IAV isolated from suckling piglets revealed an H1 hemagglutinin (HA) from the 1B.2.2.2 clade and N2 neuraminidase (NA) from the 2002A clade. The internal gene constellation of the endemic H1N2 was TTTTPT with a pandemic lineage matrix. The HA gene had 97.59% and 97.52% nucleotide and amino acid identities, respectively, to the H1 1B.2.2.2 used in the farm-specific vaccine. A similar H1 1B.2.2.2 was detected in the downstream nursery. These data demonstrate the low frequency of IAV detection in suckling piglets and downstream nurseries from farms with endemic infections in spite of using farm-specific IAV vaccines in sows.

Swine influenza A virus: challenges and novel vaccine strategies

Swine Influenza A Virus (IAV-S) imposes a significant impact on the pork industry and has been deemed a significant threat to global public health due to its zoonotic potential. The most effective method of preventing IAV-S is vaccination. While there are tremendous efforts to control and prevent IAV-S in vulnerable swine populations, there are considerable challenges in developing a broadly protective vaccine against IAV-S. These challenges include the consistent diversification of IAV-S, increasing the strength and breadth of adaptive immune responses elicited by vaccination, interfering maternal antibody responses, and the induction of vaccine-associated enhanced respiratory disease after vaccination. Current vaccination strategies are often not updated frequently enough to address the continuously evolving nature of IAV-S, fail to induce broadly cross-reactive responses, are susceptible to interference, may enhance respiratory disease, and can be expensive to produce. Here, we review the challenges and current status of universal IAV-S vaccine research. We also detail the current standard of licensed vaccines and their limitations in the field. Finally, we review recently described novel vaccines and vaccine platforms that may improve upon current methods of IAV-S control.

An Update in Knowledge of Pigs as the Source of Zoonotic Pathogens

The available data indicate that the human world population will constantly grow in the subsequent decades. This constant increase in the number of people on the Earth will lead to growth in food demand, especially in food of high nutritional value. Therefore, it is expected that the world livestock population will also increase. Such a phenomenon enhances the risk of transmitting pathogens to humans. As pig production is one of the most significant branches of the world's livestock production, zoonoses of porcine origins seem to be of particular importance. Therefore, in this review, we aim to introduce the latest data concerning, among other things, epidemiology and available preventive measures to control the most significant porcine zoonoses of viral, bacterial, and parasitic origin.

Inflammation and Microbiota Regulation Potentiate Pneumonia Therapy by Biomimetic Bacteria and Macrophage Membrane Nanosystem

While conventional nanosystems can target infected lung tissue, they cannot achieve precise cellular targeting and enhanced therapy by modulating inflammation and microbiota for effective therapy. Here, we designed a nucleus-targeted nanosystem with adenosine triphosphate (ATP) and reactive oxygen species stimuli-response to treat pneumonia coinfected with bacteria and virus that is enhanced through inflammation and microbiota regulation. The nucleus-targeted biomimetic nanosystem was prepared through the combined bacteria-macrophage membrane and loaded hypericin and ATP-responsive dibenzyl oxalate (MMHP) subsequently. The MMHP despoiled the Mg2+ of intracellular cytoplasm in bacteria to achieve an effective bactericidal performance. Meanwhile, MMHP can target the cell nucleus and inhibit the H1N1 virus duplication by inhibiting the activity of nucleoprotein. MMHP possessed an immunomodulatory ability to reduce the inflammatory response and activate CD8+ T cells for assisted infection elimination. During the mice model, the MMHP effectively treated pneumonia coinfected with Staphylococcus aureus and H1N1 virus. Meanwhile, MMHP mediated the composition of gut microbiota to enhance the pneumonia therapy. Therefore, the dual stimuli-responsive MMHP possessed promising clinical translational potential to therapy infectious pneumonia.

Vincent Baker A, Wang X, Zhu Z, Berg E, Trevisan G, Zhang J, Jayaraman S, Linhares DCL, Gauger PC, S. Silva G. Veterinarian perceptions and practices in prevention and control of influenza virus in the Midwest United States swine farms

Influenza A virus (IAV) is an endemic respiratory pathogen affecting swine worldwide and is a public health concern as a zoonotic pathogen. Veterinarians may respond to IAV infection in swine with varied approaches depending on their perception of its economic impact on human and animal health. This study considered three primary veterinary practice categories: swine exclusive veterinary practitioner, large animal practitioner, which corresponds to veterinarians that work predominantly with food animals including but not exclusively porcine, and mixed animal practitioner, which corresponds to veterinarians working with companion and food animals. This survey aimed to assess U.S. veterinarian perceptions, biosecurity practices, and control methods for IAV in swine. In this study, 54.5% (188/345) of the veterinarians that were targeted responded to all portions of the survey. The study results presented different perceptions regarding IAV among veterinarians in different types of veterinary practices and the current IAV mitigation practices implemented in swine farms based on strategic decisions. Collectively, this study also revealed the veterinarians' perceptions that IAV as a health problem in swine is increasing, IAV has a moderate economic impact, and there is a high level of concern regarding IAV circulating in swine. These findings highlight the need for IAV surveillance data, improved vaccine strategies, as well as important opportunities regarding methods of control and biosecurity. Additionally, results of this survey suggest biosecurity practices associated with the veterinarian's swine operations and prevention of zoonotic diseases can be strengthened through annual IAV vaccination of humans and support of sick leave policies for farm workers.

Bivalent hemagglutinin and neuraminidase influenza replicon particle vaccines protect pigs against influenza a virus without causing vaccine associated enhanced respiratory disease

Alphavirus-derived RNA replicon particle (RP) vaccines represent the next generation of swine influenza A virus (IAV) vaccines, as they were shown to be safe, effective, and offer advantages over traditional vaccine platforms. IAV is a significant respiratory pathogen of swine and there is a critical need to improve current commercial swine IAV vaccine platforms. Adjuvanted whole inactivated virus (WIV) IAV swine vaccines provide limited heterologous protection and may lead to vaccine-associated enhanced respiratory disease (VAERD). This study investigated the ability of RP IAV hemagglutinin (HA) vaccines to avoid VAERD and evaluated experimental multivalent HA and neuraminidase (NA) RP vaccines. RP vaccines were formulated with HA or NA heterologous or homologous to the challenge virus in monovalent HA or HA and NA bivalent combinations (HA/NA bivalent). Pigs were vaccinated with an HA RP, HA/NA bivalent RP, or heterologous HA WIV, followed by IAV challenge and necropsy 5 days post infection. RP vaccines provided homologous protection from challenge and induced robust peripheral and local antibody responses. The RP vaccine did not induce VAERD after challenge with a virus containing the heterologous HA, in contrast to the traditional WIV vaccine. The HA monovalent and HA/NA bivalent RP vaccines showed superior protection compared to traditional WIV. Additionally, the RP platform allows greater flexibility to adjust HA and NA content to reflect circulating IAV in swine antigenic diversity.

Bat influenza vectored NS1-truncated live vaccine protects pigs against heterologous virus challenge

Swine influenza is an important disease for the swine industry. Currently used whole inactivated virus (WIV) vaccines can induce vaccine-associated enhanced respiratory disease (VAERD) in pigs when the vaccine strains mismatch with the infected viruses. Live attenuated influenza virus vaccine (LAIV) is effective to protect pigs against homologous and heterologous swine influenza virus infections without inducing VAERD but has safety concerns due to potential reassortment with circulating viruses. Herein, we used a chimeric bat influenza Bat09:mH3mN2 virus, which contains both surface HA and NA gene open reading frames of the A/swine/Texas/4199-2/1998 (H3N2) and six internal genes from the novel bat H17N10 virus, to develop modified live-attenuated viruses (MLVs) as vaccine candidates which cannot reassort with canonical influenza A viruses by co-infection. Two attenuated MLV vaccine candidates including the virus that expresses a truncated NS1 (Bat09:mH3mN2-NS1-128, MLV1) or expresses both a truncated NS1 and the swine IL-18 (Bat09:mH3mN2-NS1-128-IL-18, MLV2) were generated and evaluated in pigs against a heterologous H3N2 virus using the WIV vaccine as a control. Compared to the WIV vaccine, both MLV vaccines were able to reduce lesions and virus replication in lungs and limit nasal virus shedding without VAERD, also induced significantly higher levels of mucosal IgA response in lungs and significantly increased numbers of antigen-specific IFN-γ secreting cells against the challenge virus. However, no significant difference was observed in efficacy between the MLV1 and MLV2. These results indicate that bat influenza vectored MLV vaccines can be used as a safe live vaccine to prevent swine influenza.

Swine Influenza A Viruses and the Tangled Relationship with Humans

Influenza A viruses (IAVs) are the causative agents of one of the most important viral respiratory diseases in pigs and humans. Human and swine IAV are prone to interspecies transmission, leading to regular incursions from human to pig and vice versa. This bidirectional transmission of IAV has heavily influenced the evolutionary history of IAV in both species. Transmission of distinct human seasonal lineages to pigs, followed by sustained within-host transmission and rapid adaptation and evolution, represent a considerable challenge for pig health and production. Consequently, although only subtypes of H1N1, H1N2, and H3N2 are endemic in swine around the world, extensive diversity can be found in the hemagglutinin (HA) and neuraminidase (NA) genes, as well as the remaining six genes. We review the complicated global epidemiology of IAV in swine and the inextricably entangled implications for public health and influenza pandemic planning.

Current and prospective control strategies of influenza A virus in swine

BACKGROUND

Influenza A Viruses (IAV) are endemic pathogens of significant concern in humans and multiple keystone livestock species. Widespread morbidity in swine herds negatively impacts animal welfare standards and economic performance whilst human IAV pandemics have emerged from pigs on multiple occasions. To combat the rising prevalence of swine IAV there must be effective control strategies available.

MAIN BODY

The most basic form of IAV control on swine farms is through good animal husbandry practices and high animal welfare standards. To control inter-herd transmission, biosecurity considerations such as quarantining of pigs and implementing robust health and safety systems for workers help to reduce the likelihood of swine IAV becoming endemic. Closely complementing the physical on-farm practices are IAV surveillance programs. Epidemiological data is critical in understanding regional distribution and variation to assist in determining an appropriate response to outbreaks and understanding the nature of historical swine IAV epidemics and zoonoses. Medical intervention in pigs is restricted to vaccination, a measure fraught with the intrinsic difficulties of mounting an immune response against a highly mutable virus. It is the best available tool for controlling IAV in swine but is far from being a perfect solution due to its unreliable efficacy and association with an enhanced respiratory disease. Because IAV generally has low mortality rates there is a reticence in the uptake of vaccination. Novel genetic technologies could be a complementary strategy for IAV control in pigs that confers broad-acting resistance. Transgenic pigs with IAV resistance are useful as models, however the complexity of these reaching the consumer market limits them to research models. More promising are gene-editing approaches to prevent viral exploitation of host proteins and modern vaccine technologies that surpass those currently available.

CONCLUSION

Using the suite of IAV control measures that are available for pigs effectively we can improve the economic productivity of pig farming whilst improving on-farm animal welfare standards and avoid facing the extensive social and financial costs of a pandemic. Fighting 'Flu in pigs will help mitigate the very real threat of a human pandemic emerging, increase security of the global food system and lead to healthier pigs.

Next-generation influenza vaccines: opportunities and challenges

Seasonal influenza vaccines lack efficacy against drifted or pandemic influenza strains. Developing improved vaccines that elicit broader immunity remains a public health priority. Immune responses to current vaccines focus on the haemagglutinin head domain, whereas next-generation vaccines target less variable virus structures, including the haemagglutinin stem. Strategies employed to improve vaccine efficacy involve using structure-based design and nanoparticle display to optimize the antigenicity and immunogenicity of target antigens; increasing the antigen dose; using novel adjuvants; stimulating cellular immunity; and targeting other viral proteins, including neuraminidase, matrix protein 2 or nucleoprotein. Improved understanding of influenza antigen structure and immunobiology is advancing novel vaccine candidates into human trials.

A Brief Introduction to Influenza A Virus in Swine

Influenza A viruses (IAVs) of the Orthomyxoviridae virus family cause one of the most important respiratory diseases in pigs and humans. Repeated outbreaks and rapid spread of genetically and antigenically distinct IAVs represent a considerable challenge for animal production and public health. Bidirection transmission of IAV between pigs and people has altered the evolutionary dynamics of IAV, and a "One Health" approach is required to ameliorate morbidity and mortality in both hosts and improve control strategies. Although only subtypes of H1N1, H1N2, and H3N2 are endemic in swine around the world, considerable diversity can be found not only in the hemagglutinin (HA) and neuraminidase (NA) genes but in the remaining six genes as well. Human and swine IAVs have demonstrated a particular propensity for interspecies transmission, leading to regular and sometimes sustained incursions from man to pig and vice versa. The diversity of IAVs in swine remains a critical challenge in the diagnosis and control of this important pathogen for swine health and in turn contributes to a significant public health risk.

Protection of White Leghorn chickens by recombinant fowlpox vector vaccine with an updated H5 insert against Mexican H5N2 avian influenza viruses

Despite decades of vaccination, surveillance, and biosecurity measures, H5N2 low pathogenicity avian influenza (LPAI) virus infections continue in Mexico and neighboring countries. One explanation for tenacity of H5N2 LPAI in Mexico is the antigenic divergence of circulating field viruses compared to licensed vaccines due to antigenic drift. Our phylogenetic analysis indicates that the H5N2 LPAI viruses circulating in Mexico and neighboring countries since 1994 have undergone antigenic drift away from vaccine seed strains. Here we evaluated the efficacy of a new recombinant fowlpox virus vector containing an updated H5 insert (rFPV-H5/2016), more relevant to the current strains circulating in Mexico. We tested the vaccine efficacy against a closely related subcluster 4 Mexican H5N2 LPAI (2010 H5/LP) virus and the historic H5N2 HPAI (1995 H5/HP) virus in White Leghorn chickens. The rFPV-H5/2016 vaccine provided hemagglutinin inhibition (HI) titers pre-challenge against viral antigens from both challenge viruses in almost 100% of the immunized birds, with no differences in number of birds seroconverting or HI titers among all tested doses (1.5, 2.0, and 3.1 log₁₀ mean tissue culture infectious doses/bird). The vaccine conferred 100% clinical protection and a significant decrease in oral and cloacal virus shedding from 1995 H5/HP virus challenged birds when compared to the sham controls at all tested doses. Virus shedding titers from vaccinated 2010 H5/LP virus challenged birds significantly decreased compared to sham birds especially at earlier time points. Our results confirm the efficacy of the new rFPV-H5/2016 against antigenic drift of LPAI virus in Mexico and suggest that this vaccine would be a good candidate, likely as a primer in a prime-boost vaccination program.

Efficacy of novel recombinant fowlpox vaccine against recent Mexican H7N3 highly pathogenic avian influenza virus

Since 2012, H7N3 highly pathogenic avian influenza (HPAI) has produced negative economic and animal welfare impacts on poultry in central Mexico. In the present study, chickens were vaccinated with two different recombinant fowlpox virus vaccines (rFPV-H7/3002 with 2015 H7 hemagglutinin [HA] gene insert, and rFPV-H7/2155 with 2002 H7 HA gene insert), and were then challenged three weeks later with H7N3 HPAI virus (A/chicken/Jalisco/CPA-37905/2015). The rFPV-H7/3002 vaccine conferred 100% protection against mortality and morbidity, and significantly reduced virus shed titers from the respiratory and gastrointestinal tracts. In contrast, 100% of sham and rFPV-H7/2155 vaccinated birds shed virus at higher titers and died within 4 days. Pre- (15/20) and post- (20/20) challenge serum of birds vaccinated with rFPV-H7/3002 had antibodies detectable by hemagglutination inhibition (HI) assay using challenge virus antigen. However, only a few birds (3/20) in the rFPV-H7/2155 vaccinated group had antibodies that reacted against the challenge strain but all birds had antibodies that reacted against the homologous vaccine antigen (A/turkey/Virginia/SEP-66/2002) (20/20). One possible explanation for differences in vaccines efficacy is the antigenic drift between circulating viruses and vaccines. Molecular analysis demonstrated that the Mexican H7N3 strains have continued to rapidly evolve since 2012. In addition, we identified in silico three potential new N-glycosylation sites on the globular head of the H7 HA of A/chicken/Jalisco/CPA-37905/2015 challenge virus, which were absent in 2012 H7N3 outbreak virus. Our results suggested that mutations in the HA antigenic sites including increased glycosylation sites, accumulated in the new circulating Mexican H7 HPAIV strains, altered the recognition of neutralizing antibodies from the older vaccine strain rFPV-H7/2155. Therefore, the protective efficacy of novel rFPV-H7/3002 against recent outbreak Mexican H7N3 HPAIV confirms the importance of frequent updating of vaccines seed strains for long-term effective control of H7 HPAI virus.

Alphavirus-vectored hemagglutinin subunit vaccine provides partial protection against heterologous challenge in pigs

Influenza A virus in swine (IAV-S) is an important pathogen in pigs in the United States, in addition to posing a potential risk to humans through zoonotic events. Intervention strategies continue to be explored to better control virus circulation. Improved surveillance efforts has led to significantly increased sequence data available on circulating strains, vastly improving our understanding of the genetic and antigenic diversity of IAV-S. IAV-S in North America is characterized by repeated spillover events of human viruses into pigs followed by genetic and antigenic diversification. An important gap that needs to be addressed is our understanding of the role that various vaccine platforms have on efficacy against antigenically heterologous challenge. Currently licensed vaccines often update their components to adapt to a dynamic antigenic landscape and newly developed technologies continue to be approved. Hence, it remains critical to test the performance of vaccines against challenge with antigenically distinct viruses. We tested the level of protection conferred by an alphavirus-vectored hemagglutinin (HA) subunit vaccine, delivered as a monovalent or bivalent formulation, against challenge with IAV-S. Monovalent alphavirus-vectored HA vaccines provided efficient protection against challenge with viruses with matched and mismatched HA, although in one mismatched HA challenge group there was a trend for reduced protection. A bivalent vaccine, in which two HA's were simultaneously delivered, was effective in producing antibody response against both antigens and provided protection against challenge. The alphavirus platform is a promising new technology available to swine producers to help reduce the burden of disease caused by IAV-S.

Evaluation of an African swine fever (ASF) vaccine strategy incorporating priming with an alphavirus-expressed antigen followed by boosting with attenuated ASF virus

In this study, an alphavirus vector platform was used to deliver replicon particles (RPs) expressing African swine fever virus (ASFV) antigens to swine. Alphavirus RPs expressing ASFV p30 (RP-30), p54 (RP-54) or pHA-72 (RP-sHA-p72) antigens were constructed and tested for expression in Vero cells and for immunogenicity in pigs. RP-30 showed the highest expression in Vero cells and was the most immunogenic in pigs, followed by RP-54 and RP-sHA-p72. Pigs primed with two doses of the RP-30 construct were then boosted with a naturally attenuated ASFV isolate, OURT88/3. Mapping of p30 identified an immunodominant region within the amino acid residues 111-130. However, the principal effect of the prime-boost was enhanced recognition of an epitope covered by the peptide sequence 61-110. The results suggest that a strategy incorporating priming with a vector-expressed antigen followed by boosting with an attenuated live virus may broaden the recognition of ASFV epitopes.

The type of adjuvant in whole inactivated influenza a virus vaccines impacts vaccine-associated enhanced respiratory disease

Influenza A virus (IAV) causes a disease burden in the swine industry in the US and is a challenge to prevent due to substantial genetic and antigenic diversity of IAV that circulate in pig populations. Whole inactivated virus (WIV) vaccines formulated with oil-in-water (OW) adjuvant are commonly used in swine. However, WIV-OW are associated with vaccine-associated enhanced respiratory disease (VAERD) when the hemagglutinin and neuraminidase of the vaccine strain are mismatched with the challenge virus. Here, we assessed if different types of adjuvant in WIV vaccine formulations impacted VAERD outcome. WIV vaccines with a swine δ1-H1N2 were formulated with different commercial adjuvants: OW1, OW2, nano-emulsion squalene-based (NE) and gel polymer (GP). Pigs were vaccinated twice by the intramuscular route, 3 weeks apart, then challenged with an H1N1pdm09 three weeks post-boost and necropsied at 5 days post infection. All WIV vaccines elicited antibodies detected using the hemagglutination inhibition (HI) assay against the homologous vaccine virus, but not against the heterologous challenge virus; in contrast, all vaccinated groups had cross-reactive IgG antibody and IFN-γ responses against H1N1pdm09, with a higher magnitude observed in OW groups. Both OW groups demonstrated robust homologous HI titers and cross-reactivity against heterologous H1 viruses in the same genetic lineage. However, both OW groups had severe immunopathology consistent with VAERD after challenge when compared to NE, GP, and non-vaccinated challenge controls. None of the WIV formulations protected pigs from heterologous virus replication in the lungs or nasal cavity. Thus, although the type of adjuvant in the WIV formulation played a significant role in the magnitude of immune response to homologous and antigenically similar H1, none tested here increased the breadth of protection against the antigenically-distinct challenge virus, and some impacted immunopathology after challenge.

Universal Vaccines and Vaccine Platforms to Protect against Influenza Viruses in Humans and Agriculture

Influenza virus infections pose a significant threat to public health due to annual seasonal epidemics and occasional pandemics. Influenza is also associated with significant economic losses in animal production. The most effective way to prevent influenza infections is through vaccination. Current vaccine programs rely heavily on the vaccine's ability to stimulate neutralizing antibody responses to the hemagglutinin (HA) protein. One of the biggest challenges to an effective vaccination program lies on the fact that influenza viruses are ever-changing, leading to antigenic drift that results in escape from earlier immune responses. Efforts toward overcoming these challenges aim at improving the strength and/or breadth of the immune response. Novel vaccine technologies, the so-called universal vaccines, focus on stimulating better cross-protection against many or all influenza strains. However, vaccine platforms or manufacturing technologies being tested to improve vaccine efficacy are heterogeneous between different species and/or either tailored for epidemic or pandemic influenza. Here, we discuss current vaccines to protect humans and animals against influenza, highlighting challenges faced to effective and uniform novel vaccination strategies and approaches.

Virus replicon particle vaccines expressing nucleoprotein of influenza A virus mediate enhanced inflammatory responses in pigs

Studies in the mouse model indicate that the nucleoprotein of influenza A virus represents an interesting vaccine antigen being well conserved across subtypes of influenza virus but still able to induce protective immune responses. Here we show that immunizations of pigs with vesicular stomatitis virus- and classical swine fever virus-derived replicon (VRP) particles expressing the nucleoprotein (NP) of H1N1 A/swine/Belzig/2/01 induced potent antibody and T-cell responses against influenza A virus. In contrast to a conventional whole inactivated virus vaccine, the VRP vaccines induced both NP-specific CD4 and CD8 T cells responses, including interferon-γ and tumor-necrosis-factor dual-secreting cell. Although T-cells and antibody responses were cross-reactive with the heterologous H1N2 A/swine/Bakum/R757/2010 challenge virus, they did not provide protection against infection. Surprisingly, vaccinated pigs showed enhanced virus shedding, lung inflammation and increased levels of systemic and lung interferon-α as well as elevated lung interleukin-6. In conclusion, our study shows that NP, although efficacious in the mouse model, appears not to be a promising stand-alone vaccine antigen for pigs.

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.

Viral vector-based influenza vaccines

Antigenic drift of seasonal influenza viruses and the occasional introduction of influenza viruses of novel subtypes into the human population complicate the timely production of effective vaccines that antigenically match the virus strains that cause epidemic or pandemic outbreaks. The development of game-changing vaccines that induce broadly protective immunity against a wide variety of influenza viruses is an unmet need, in which recombinant viral vectors may provide. Use of viral vectors allows the delivery of any influenza virus antigen, or derivative thereof, to the immune system, resulting in the optimal induction of virus-specific B- and T-cell responses against this antigen of choice. This systematic review discusses results obtained with vectored influenza virus vaccines and advantages and disadvantages of the currently available viral vectors.

Expression of H3N2 nucleoprotein in maize seeds and immunogenicity in mice

Oral administration of maize-expressed H3N2 nucleoprotein induced antibody responses in mice showing the immunogenicity of plant-derived antigen and its potential to be utilized as a universal flu vaccine. Influenza A viruses cause influenza epidemics that are devastating to humans and livestock. The vaccine for influenza needs to be reformulated every year to match the circulating strains due to virus mutation. Influenza virus nucleoprotein (NP) is a multifunctional RNA-binding protein that is highly conserved among strains, making it a potential candidate for a universal vaccine. In this study, the NP gene of H3N2 swine origin influenza virus was expressed in maize endosperm. Twelve transgenic maize lines were generated and analyzed for recombinant NP (rNP) expression. Transcript analysis showed the main accumulation of rNP in seed. Protein level of rNP in T1 transgenic maize seeds ranged from 8.0 to 35 µg of NP/g of corn seed. The level increased up to 70 µg of NP/g in T3 seeds. A mouse study was performed to test the immunogenicity of one line of maize-derived rNP (MNP). Mice were immunized with MNP in a prime-boost design. Oral gavage administration showed that a humoral immune response was elicited in the mice treated with MNP indicating the immunogenicity of MNP. NP-specific antibody responses in the MNP group showed comparable antibody titer with the groups receiving positive controls such as Vero cell-derived NP (VNP) or alphavirus replicon particle-derived NP (ANP). Cytokine analysis showed antigen-specific stimulation of IL-4 cytokine elicited in splenocytes from mice treated with MNP further confirming a TH2 humoral immune response induced by MNP administration.

Vaccines against influenza A viruses in poultry and swine: Status and future developments

Influenza A viruses are important pathogens with a very broad host spectrum including domestic poultry and swine. For preventing clinical disease and controlling the spread, vaccination is one of the most efficient tools. Classical influenza vaccines for domestic poultry and swine are conventional inactivated preparations. However, a very broad range of novel vaccine types ranging from (i) nucleic acid-based vaccines, (ii) replicon particles, (iii) subunits and virus-like particles, (iv) vectored vaccines, or (v) live-attenuated vaccines has been described, and some of them are now also used in the field. The different novel approaches for vaccines against avian and swine influenza virus infections are reviewed, and additional features like universal vaccines, novel application approaches and the "differentiating infected from vaccinated animals" (DIVA)-strategy are summarized.

RNA-based viral vectors

The advent of reverse genetic approaches to manipulate the genomes of both positive (+) and negative (-) sense RNA viruses allowed researchers to harness these genomes for basic research. Manipulation of positive sense RNA virus genomes occurred first largely because infectious RNA could be transcribed directly from cDNA versions of the RNA genomes. Manipulation of negative strand RNA virus genomes rapidly followed as more sophisticated approaches to provide RNA-dependent RNA polymerase complexes coupled with negative-strand RNA templates were developed. These advances have driven an explosion of RNA virus vaccine vector development. That is, development of approaches to exploit the basic replication and expression strategies of RNA viruses to produce vaccine antigens that have been engineered into their genomes. This study has led to significant preclinical testing of many RNA virus vectors against a wide range of pathogens as well as cancer targets. Multiple RNA virus vectors have advanced through preclinical testing to human clinical evaluation. This review will focus on RNA virus vectors designed to express heterologous genes that are packaged into viral particles and have progressed to clinical testing.

Pathogenesis and vaccination of influenza A virus in swine

Swine influenza is an acute respiratory disease of pigs caused by influenza A virus (IAV) and characterized by fever followed by lethargy, anorexia, and serous nasal discharge. The disease progresses rapidly and may be complicated when associated with other respiratory pathogens. IAV is one of the most prevalent respiratory pathogens of swine, resulting in substantial economic burden to pork producers. In the past 10-15 years, a dramatic evolution of the IAV in U.S. swine has occurred, resulting in the co-circulation of many antigenically distinct IAV strains, derived from 13 phylogenetically distinct hemagglutinin clusters of H1 and H3 viruses. Vaccination is the most common strategy to prevent influenza in pigs, however, the current diverse IAV epidemiology poses a challenge for the production of efficacious and protective vaccines. A concern regarding the use of traditional inactivated vaccines is the possibility of inducing vaccine-associated enhanced respiratory disease (VAERD) when vaccine virus strains are mismatched with the infecting strain. In this review, we discuss the current epidemiology and pathogenesis of swine influenza in the United States, different vaccines platforms with potential to control influenza in pigs, and the factors associated with vaccine-associated disease enhancement.