A prime-boost concept using a T-cell epitope-driven DNA vaccine followed by a whole virus vaccine effectively protected pigs in the pandemic H1N1 pig challenge model

Influenza A virus (IAV) vaccines in pigs generally provide homosubtypic protection but fail to prevent heterologous infections. In this pilot study, the efficacy of an intradermal pDNA vaccine composed of conserved SLA class I and class II T cell epitopes (EPITOPE) against a homosubtypic challenge was compared to an intramuscular commercial inactivated whole virus vaccine (INACT) and a heterologous prime boost approach using both vaccines. Thirty-nine IAV-free, 3-week-old pigs were randomly assigned to one of five groups including NEG-CONTROL (unvaccinated, sham-challenged), INACT-INACT-IAV (vaccinated with FluSure XP® at 4 and 7 weeks, pH1N1 challenged), EPITOPE-INACT-IAV (vaccinated with PigMatrix EDV at 4 and FluSure XP® at 7 weeks, pH1N1 challenged), EPITOPE-EPITOPE-IAV (vaccinated with PigMatrix EDV at 4 and 7 weeks, pH1N1 challenged), and a POS-CONTROL group (unvaccinated, pH1N1 challenged). The challenge was done at 9 weeks of age and pigs were necropsied at day post challenge (dpc) 5. At the time of challenge, all INACT-INACT-IAV pigs, and by dpc 5 all EPITOPE-INACT-IAV pigs were IAV seropositive. IFNγ secreting cells, recognizing vaccine epitope-specific peptides and pH1N1 challenge virus were highest in the EPITOPE-INACT-IAV pigs at challenge. Macroscopic lung lesion scores were reduced in all EPITOPE-INACT-IAV pigs while INACT-INACT-IAV pigs exhibited a bimodal distribution of low and high scores akin to naïve challenged animals. No IAV antigen in lung tissues was detected at necropsy in the EPITOPE-INACT-IAV group, which was similar to naïve unchallenged pigs and different from all other challenged groups. Results suggest that the heterologous prime boost approach using an epitope-driven DNA vaccine followed by an inactivated vaccine was effective against a homosubtypic challenge, and further exploration of this vaccine approach as a practical control measure against heterosubtypic IAV infections is warranted.     

Heterologous prime-boost immunization of Newcastle disease virus vectored vaccines protected broiler chickens against highly pathogenic avian influenza and Newcastle disease viruses

Avian Influenza virus (AIV) is an important pathogen for both human and animal health. There is a great need to develop a safe and effective vaccine for AI infections in the field. Live-attenuated Newcastle disease virus (NDV) vectored AI vaccines have shown to be effective, but preexisting antibodies to the vaccine vector can affect the protective efficacy of the vaccine in the field. To improve the efficacy of AI vaccine, we generated a novel vectored vaccine by using a chimeric NDV vector that is serologically distant from NDV. In this study, the protective efficacy of our vaccines was evaluated by using H5N1 highly pathogenic avian influenza virus (HPAIV) strain A/Vietnam/1203/2004, a prototype strain for vaccine development. The vaccine viruses were three chimeric NDVs expressing the hemagglutinin (HA) protein in combination with the neuraminidase (NA) protein, matrix 1 protein, or nonstructural 1 protein. Comparison of their protective efficacy between a single and prime-boost immunizations indicated that prime immunization of 1-day-old SPF chicks with our vaccine viruses followed by boosting with the conventional NDV vector strain LaSota expressing the HA protein provided complete protection of chickens against mortality, clinical signs and virus shedding. Further verification of our heterologous prime-boost immunization using commercial broiler chickens suggested that a sequential immunization of chickens with chimeric NDV vector expressing the HA and NA proteins following the boost with NDV vector expressing the HA protein can be a promising strategy for the field vaccination against HPAIVs and against highly virulent NDVs.     

Development of in ovo-compatible NS1-truncated live attenuated influenza vaccines by modulation of hemagglutinin cleavage and polymerase acidic X frameshifting sites

Emerging avian influenza viruses pose a high risk to poultry production, necessitating the need for more broadly protective vaccines. Live attenuated influenza vaccines offer excellent protective efficacies but their use in poultry farms is discouraged due to safety concerns related to emergence of reassortant viruses. Vaccination of chicken embryos inside eggs (in ovo) induces early immunity in young chicks while reduces the safety concerns related to the use of live vaccines on farms. However, in ovo vaccination using influenza viruses severely affects the egg hatchability. We previously engineered a high interferon-inducing live attenuated influenza vaccine candidate with an enhanced protective efficacy in chickens. Here, we asked whether we could further modify this high interferon-inducing vaccine candidate to develop an in ovo-compatible live attenuated influenza vaccine. We first showed that the enhanced interferon responses induced by the vaccine is not enough to attenuate the virus in ovo. To reduce the pathogenicity of the virus for chicken embryos, we replaced the hemagglutinin cleavage site of the H7 vaccine virus (PENPKTR/GL) with that of the H6-subtype viruses (PQIETR/GL) and disrupted the ribosomal frameshifting site responsible for viral polymerase acidic X protein expression. In ovo vaccination of chickens with up to 10⁵ median egg infectious dose of the modified vaccine had minimal effects on hatchability while protecting the chickens against a heterologous challenge virus at two weeks of age. This study demonstrates that targeted genetic mutations can be applied to further attenuate and enhance the safety of live attenuated influenza vaccines to develop future in ovo vaccines for poultry.     

Impact of prior flavivirus vaccination on immunogenicity and efficacy of an inactivated Zika vaccine in Indian rhesus macaques

Flaviviruses are antigenically related. We evaluated the immunogenicity and efficacy of Takeda’s purified inactivated Zika vaccine (PIZV) candidate in macaques previously vaccinated with several commercially available heterologous flavivirus vaccines. Heterologous flavivirus vaccination did not elicit Zika virus (ZIKV) neutralizing antibodies and did not impact neutralizing antibody titers after one dose of PIZV. After a second PIZV dose previous vaccination with flavivirus vaccines had variable impact on ZIKV neutralizing antibody titers. However, all macaques were protected against viremia after Zika virus challenge 8–12 months post-PIZV vaccination. Therefore, vaccine-induced immunity against heterologous flavivirus vaccines does not impact PIZV efficacy in macaques.     

Single-replication BM2SR vaccine provides sterilizing immunity and cross-lineage influenza B virus protection in mice

Both influenza A and B viruses cause outbreaks of seasonal influenza resulting in significant morbidity and mortality. There are two antigenically distinct lineages of influenza B virus, Yamagata lineage (YL) and Victoria lineage (VL). Since both B lineages have been co-circulating for years, more than 70% of influenza vaccines currently manufactured are quadrivalent consisting of influenza A (H1N1), influenza A (H3N2), influenza B (YL) and influenza B (VL) antigens. Although quadrivalent influenza vaccines tend to elevate immunity to both influenza B lineages, estimated overall vaccine efficacy against influenza B is still only around 42%. Thus, a more effective influenza B vaccine is needed.To meet this need, we generated BM2-deficient, single-replication (BM2SR) influenza B vaccine viruses that encode surface antigens from influenza B/Wisconsin/01/2010 (B/WI01, YL) and B/Brisbane/60/2008 (B/Bris60, VL) viruses. The BM2SR-WI01 and BM2SR-Bris60 vaccine viruses are replication-deficient in vitro and in vivo, and can only replicate in a cell line that expresses the complementing BM2 protein. Both BM2SR viruses were non-pathogenic to mice, and vaccinated animals showed elevated mucosal and serum antibody responses to both Yamagata and Victoria lineages in addition to cellular responses. Serum antibody responses included lineage-specific hemagglutinin inhibition antibody (HAI) responses as well as responses to the stem region of the hemagglutinin (HA). BM2SR vaccine viruses provided apparent sterilizing immunity to mice against intra- and inter-lineage drifted B virus challenge. The data presented here support the feasibility of BM2SR as a platform for next-generation trivalent influenza vaccine development.     

Towards a mechanistic understanding of the synergistic response induced by bivalent Marek’s disease vaccines to prevent lymphomas

BackgroundMarek’s disease (MD) is a lymphoproliferative disease of chickens caused by Marek’s disease virus (MDV), an oncogenic α-herpesvirus. Since 1970, MD has been controlled by widespread vaccination; however, more effective MD vaccines are needed to counter more virulent MDV strains. The bivalent vaccine combination of SB-1 and herpesvirus of turkey (HVT) strain FC126 has been widely used. Nonetheless, the mechanism(s) underlying this synergistic effect has not been investigated.MethodsThree experiments were conducted where SB-1 or HVT were administered as monovalent or bivalent vaccines to newly hatched chickens, then challenged five days later with MDV. In Experiment 1, levels of MDV replication in PBMCs were measured over time, and tumor incidence and vaccinal protection determined. In Experiment 2, MDV and vaccine strains replication levels in lymphoid organs were measured at 1, 5, 10, and 14 days post-challenge (DPC). In Experiment 3, to verify that the bursa was necessary for HVT protection, a subset of chicks were bursectomized and these birds plus controls were similarly vaccinated and challenged, and the levels of vaccinal protection determined.ResultsThe efficacy of bivalent SB-1 + HVT surpasses that of either SB-1 or HVT monovalent vaccines in controlling the level of pathogenic MDV in PBMCs until the end of the study, and this correlated with the ability to inhibit tumor formation. SB-1 replication in the spleen increased from 1 to 14 DPC, while HVT replicated only in the bursa at 1 DPC. The bursa was necessary for immune protection induced by HVT vaccine.ConclusionSynergy of SB-1 and HVT vaccines is due to additive influences of the individual vaccines acting at different times and target organs. And the bursa is vital for HVT to replicate and induce immune protection.     

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.     

Identification of potent epitopes on hexon capsid protein and their evaluation as vaccine candidates against infections caused by members of Adenoviridae family

Adenoviruses cause economically important diseases in vertebrates. Effective vaccines against adenoviral diseases are currently lacking. Here, we report a highly conserved epitopic region on hexon proteins of adenoviruses that generate a strong immune response when used as a virus-like-particle (VLP) vaccine, produced by inserting the epitopic region into the core protein of hepatitis B virus. For evaluation of its protective efficacy, the epitopic region from a representative adenovirus, fowl adenovirus serotype 4 (FAdV-4), was tested as a VLP vaccine which conferred 90% protection against challenge with a virulent FAdV-4 isolate in chickens. Importantly, such a high level of protection is not achieved when the epitopic region is employed as a part of a subunit vaccine. As the sequence and the structure of the epitopic region are highly conserved in hexon proteins of adenoviruses, the epitopic region could be employed as a promising VLP vaccine candidate against adenoviral diseases, in general.     

Vaccination with a fowl adenovirus chimeric fiber protein (crecFib-4/11) simultaneously protects chickens against hepatitis-hydropericardium syndrome (HHS) and inclusion body hepatitis (IBH)

In the past decades, fowl adenovirus (FAdV)-related diseases became an increasing concern for the poultry industry worldwide. Various immunization strategies against FAdVs have been experimentally investigated, with a particular focus on subunit vaccines against hepatitis-hydropericardium syndrome (HHS), caused by FAdV serotype 4, and inclusion body hepatitis (IBH), caused by serotypes 2, 8a, 8b and 11. In this study, we extended our innovative concept of recombinant chimeric fiber proteins to design a novel chimera combining epitopes from two distinct serotypes, FAdV-4 and -11, and we investigated its efficacy to simultaneously protect chickens against HHS and IBH. Specific pathogen-free chickens were vaccinated with the novel recombinant chimeric fiber and subsequently challenged with either a HHS- or IBH-causing strain. Vaccinated/challenged birds exhibited a reduction of clinical signs, limited hepatomegaly and lower levels of AST compared to the respective challenge controls. Furthermore, the vaccine prevented atrophy of HHS-affected lymphoid organs, such as thymus and bursa of Fabricius, and viral load in the target organs was significantly reduced. Clinical protection was associated with high levels of pre-challenge antibodies measured on ELISA plates coated with the vaccination antigen. Interestingly, the development of neutralizing antibodies was limited against FAdV-11 and absent against FAdV-4, indicating that protection granted by such an antigen may be linked to different immunization pathways. In conclusion, we proved that the concept of chimeric fiber vaccines can be extended across viral species boundaries and represents the first single-component FAdV subunit vaccine providing comprehensive protection against different FAdV-associated diseases.     

Factors associated with COVID-19 vaccination during June–October 2021: A multi-site prospective study

IntroductionVaccine hesitancy presents a challenge to COVID-19 control efforts. To identify beliefs associated with delayed vaccine uptake, we developed and implemented a vaccine hesitancy survey for the COVID-19 Community Research Partnership.MethodsIn June 2021, we assessed attitudes and beliefs associated with COVID-19 vaccination using an online survey. Self-reported vaccination data were requested daily through October 2021. We compared responses between vaccinated and unvaccinated respondents using absolute standardized mean differences (ASMD). We assessed validity and reliability using exploratory factor analysis and identified latent factors associated with a subset of survey items. Cox proportional hazards models and mediation analyses assessed predictors of subsequent vaccination among those initially unvaccinated.ResultsIn June 2021, 29,522 vaccinated and 1,272 unvaccinated participants completed surveys. Among those unvaccinated in June 2021, 559 (43.9 %) became vaccinated by October 31, 2021. In June, unvaccinated participants were less likely to feel “very concerned” about getting COVID-19 than vaccinated participants (10.6 % vs. 43.3 %, ASMD 0.792). Among those initially unvaccinated, greater intent to become vaccinated was associated with getting vaccinated and shorter time to vaccination. However, even among participants who reported no intention to become vaccinated, 28.5 % reported vaccination before study end. Two latent factors predicted subsequent vaccination—being ‘more receptive’ was derived from motivation to protect one’s own or others’ health and resume usual activities; being ‘less receptive’ was derived from concerns about COVID-19 vaccines. In a Cox model, both factors were partially mediated by vaccination intention.ConclusionThis study characterizes vaccine hesitant individuals and identifies predictors of eventual COVID-19 vaccination through October 31, 2021. Even individuals with no intention to be vaccinated can shift to vaccine uptake. Our data suggest factors of perceived severity of COVID-19 disease, vaccine safety, and trust in the vaccine development process are predictive of vaccination and may be important opportunities for ongoing interventions.     

Strategic silences,eroded trust: The impact of divergent COVID-19 vaccine sentiments on healthcare workers' relations with peers and patients

BackgroundPolarized debates about Covid-19 vaccination and vaccine mandates for healthcare workers (HCWs) challenge Belgian HCWs ability to discuss Covid-19 vaccine sentiments with peers and patients. Although studies have identified drivers of HCWs vaccine hesitancy, they do not include effects of workplace interactions and have not addressed consequences beyond vaccine coverage.MethodsInterviews and focus group discussions with 74 HCWs practicing in Belgium addressed Covid-19 vaccine sentiments and experiences of discussing vaccination with peers and patients.ResultsMost participating HCWs reported difficulties discussing Covid-19 vaccination with peers and patients. Unvaccinated HCWs often feared that expressing their vaccine sentiments might upset patients or peers and that they would be suspended. Consequently, they used social cues to evaluate others’ openness to vaccine-skeptical discourses and avoided discussing vaccines. Surprisingly, some vaccine-confident HCWs hid their vaccine sentiments to avoid peer and patient conflicts. Both vaccinated and unvaccinated HCWs observed that unvaccinated patients occasionally received suboptimal care. Suboptimal care was central in unvaccinated HCW unwillingness to express their vaccine sentiments to peers. Both vaccinated and unvaccinated HCWs described loss of trust and ruptured social relations with peers and patients holding divergent vaccine sentiments.DiscussionBelgian HCW perceived Covid-19 vaccines as a risky discussion topic and engaged in “strategic silences” around vaccination to maintain functional work relationships and employment in health institutions. Loss of trust between HCW and peers or patients, along with suboptimal patient care based on vaccination status, threaten to weaken Belgium’s, and by implication, other health systems, and to catalyze preventable disease outbreaks.     

Glucopyranosyl lipid adjuvant enhances immune response to Ebola virus-like particle vaccine in mice

The identification of adjuvants that promote lasting antigen-specific immunity and augment vaccine efficacy are integral to the development of new protein-based vaccines. The Ebola virus-like particle (VLP) vaccine expressing Ebola virus glycoprotein (GP) and matrix protein (VP40) was used in this study to evaluate the ability of TLR4 agonist glucopyranosyl lipid adjuvant (GLA) formulated in a stable emulsion (SE) to enhance immunogenicity and promote durable protection against mouse-adapted Ebola virus (ma-EBOV). Antibody responses and Ebola-specific T cell responses were evaluated post vaccination. Survival analysis after lethal ma-EBOV challenge was performed 4 weeks and 22 weeks following final vaccination. GLA-SE enhanced EBOV-specific immunity and resulted in long-term protection against challenge with ma-EBOV infection in a mouse model. Specifically, GLA-SE elicited Th1-skewed antibodies and promoted the generation of EBOV GP-specific polyfunctional T cells. These results provide further support for the utility of TLR4 activating GLA-SE-adjuvanted vaccines.     

Comparison of adjuvants to optimize influenza neutralizing antibody responses

Seasonal influenza vaccines represent a positive intervention to limit the spread of the virus and protect public health. Yet continual influenza evolution and its ability to evade immunity pose a constant threat. For these reasons, vaccines with improved potency and breadth of protection remain an important need. We previously developed a next-generation influenza vaccine that displays the trimeric influenza hemagglutinin (HA) on a ferritin nanoparticle (NP) to optimize its presentation. Similar to other vaccines, HA-nanoparticle vaccine efficacy is increased by the inclusion of adjuvants during immunization. To identify the optimal adjuvants to enhance influenza immunity, we systematically analyzed TLR agonists for their ability to elicit immune responses. HA-NPs were compatible with nearly all adjuvants tested, including TLR2, TLR4, TLR7/8, and TLR9 agonists, squalene oil-in-water mixtures, and STING agonists. In addition, we chemically conjugated TLR7/8 and TLR9 ligands directly to the HA-ferritin nanoparticle. These TLR agonist-conjugated nanoparticles induced stronger antibody responses than nanoparticles alone, which allowed the use of a 5000-fold-lower dose of adjuvant than traditional admixtures. One candidate, the oil-in-water adjuvant AF03, was also tested in non-human primates and showed strong induction of neutralizing responses against both matched and heterologous H1N1 viruses. These data suggest that AF03, along with certain TLR agonists, enhance strong neutralizing antibody responses following influenza vaccination and may improve the breadth, potency, and ultimately vaccine protection in humans.     

Successful reproduction of adenoviral gizzard erosion in 20-week-old SPF layer-type chickens and efficacious prophylaxis due to live vaccination with an apathogenic fowl adenovirus serotype 1 strain (CELO)

Recently, outbreaks of adenoviral gizzard erosion (AGE) have been documented in pullets and layers housed free range and in enriched cage systems characterized by increased mortality and a negative impact on egg production. In the present study the pathogenicity of a fowl adenovirus serotype 1 (FAdV-1) field strain as well as the aetiological role of a FAdV-8a strain, both isolated from AGE affected pullets, were investigated in vivo in 20-week-old specific-pathogen-free (SPF) layer-type chickens. Furthermore, the efficacy of a single (week 17) and double (week 14 and 17) application of a live vaccine consisting of an apathogenic FAdV-1 (CELO strain) against challenge with virulent FAdV-1 was investigated.For the first time, AGE was successfully reproduced in adult birds after oral infection of 20-week-old SPF birds with a virulent FAdV-1 field isolate, characterized by pathological changes of the gizzard from 7 days post challenge onwards. In addition, a negative impact of the FAdV-1 infection on the development of the reproductive tract was observed. Thus, confirming the pathogenicity and aetiological role of FAdV-1 in the development of AGE and economic losses due to AGE in layers. In contrast, no pathological changes were observed in birds infected with FAdV-8a.Independent of a single or double application of the live FAdV-1 vaccine strain CELO, no gross pathological changes were observed in gizzards post challenge with the virulent FAdV-1, indicating that complete protection of layers against horizontal induction of AGE was achieved. Nonetheless, virulent FAdV-1 was detected in cloacal swabs and gizzards in both vaccinated groups post challenge determined by the application of an amplification refractory mutation system quantitative PCR used to differentiate between vaccine and challenge strains.     

Effectiveness of Covid-19 vaccines against symptomatic and asymptomatic SARS-CoV-2 infections in an urgent care setting

BackgroundIt is critical to monitor changes in vaccine effectiveness against COVID-19 outcomes for various vaccine products in different population subgroups.MethodsWe conducted a retrospective study in patients ≥12 years who underwent testing for SARS-CoV-2 virus from April 14 through October 25, 2021, at urgent care centers in the New York metropolitan area. Patients self-reported vaccination status at the time of testing. We used a test-negative design to estimate vaccine effectiveness (VE) by comparing odds of a positive test for SARS-CoV-2 infection among vaccinated (n = 474,805), partially vaccinated (n = 87,834), and unvaccinated (n = 369,333) patients, adjusted for demographic factors and calendar time.ResultsVE against symptomatic infection after 2 doses of mRNA vaccine was 96% (95% Confidence Interval: 95%, 97%) in the pre-delta period and reduced to 79% (95% CI: 77%, 81%) in the delta period. In the delta period, VE for 12–15-year-olds (85%; [95% CI: 81%, 88%]) was higher compared to older age groups (<65% for all other age groups). VE estimates did not differ by sex and race/ethnicity. VE against symptomatic infection was the highest for individuals with a prior infection followed by full vaccination. VE against symptomatic infection after the 2-dose mRNA-1273 vaccine (82% [95% CI: 80%, 84%]) was higher compared to the BNT162b2 vaccine (76% [95% CI: 74%, 78%]) in the delta period. VE after 1-dose of the Ad26.COV2.S vaccine was the lowest compared to other vaccines (19% [95% CI: 15%, 23%]) in the delta period.ConclusionsVE against infection after two doses of the mRNA vaccines was high initially, but significantly reduced against the delta variant for both FDA-approved vaccines.     

Inactivated whole influenza virus particle vaccines induce neutralizing antibodies with an increase in immunoglobulin gene subclones of B-lymphocytes in cynomolgus macaques

The All-Japan Influenza Vaccine Study Group has been developing a more effective vaccine than the current split vaccines for seasonal influenza virus infection. In the present study, the efficacy of formalin- and/or β-propiolactone-inactivated whole virus particle vaccines for seasonal influenza was compared to that of the current ether-treated split vaccines in a nonhuman primate model. The monovalent whole virus particle vaccines or split vaccines of influenza A virus (H1N1) and influenza B virus (Victoria lineage) were injected subcutaneously into naïve cynomolgus macaques twice. The whole virus particle vaccines induced higher titers of neutralizing antibodies against H1N1 influenza A virus and influenza B virus in the plasma of macaques than did the split vaccines. At challenge with H1N1 influenza A virus or influenza B virus, the virus titers in nasal swabs and the increases in body temperatures were lower in the macaques immunized with the whole virus particle vaccine than in those immunized with the split vaccine. Repertoire analyses of immunoglobulin heavy chain genes demonstrated that the number of B-lymphocyte subclones was increased in macaques after the 1st vaccination with the whole virus particle vaccine, but not with the split vaccine, indicating that the whole virus particle vaccine induced the activation of vaccine antigen-specific B-lymphocytes more vigorously than did the split vaccine at priming. Thus, the present findings suggest that the superior antibody induction ability of the whole virus particle vaccine as compared to the split vaccine is attributable to its stimulatory properties on the subclonal differentiation of antigen-specific B-lymphocytes.     

Vaccine protection of chickens against antigenically diverse H5 highly pathogenic avian influenza isolates with a live HVT vector vaccine expressing the influenza hemagglutinin gene derived from a clade 2.2 avian influenza virus

Vaccination is an important tool in the protection of poultry against avian influenza (AI). For field use, the overwhelming majority of AI vaccines produced are inactivated whole virus formulated into an oil emulsion. However, recombinant vectored vaccines are gaining use for their ability to induce protection against heterologous isolates and ability to overcome maternal antibody interference. In these studies, we compared protection of chickens provided by a turkey herpesvirus (HVT) vector vaccine expressing the hemagglutinin (HA) gene from a clade 2.2 H5N1 strain (A/swan/Hungary/4999/2006) against homologous H5N1 as well as heterologous H5N1 and H5N2 highly pathogenic (HP) AI challenge. The results demonstrated all vaccinated birds were protected from clinical signs of disease and mortality following homologous challenge. In addition, oral and cloacal swabs taken from challenged birds demonstrated that vaccinated birds had lower incidence and titers of viral shedding compared to sham-vaccinated birds. Following heterologous H5N1 or H5N2 HPAI challenge, 80–95% of birds receiving the HVT vector AI vaccine at day of age survived challenge with fewer birds shedding virus after challenge than sham vaccinated birds. In vitro cytotoxicity analysis demonstrated that splenic T lymphocytes from HVT-vector-AI vaccinated chickens recognized MHC-matched target cells infected with H5, as well as H6, H7, or H9 AI virus. Taken together, these studies provide support for the use of HVT vector vaccines expressing HA to protect poultry against multiple lineages of HPAI, and that both humoral and cellular immunity induced by live vaccines likely contributes to protection.     

Evaluation of five circulating strains of variant infectious bursal disease virus (varIBDV) for their immunogenicity as broiler breeder vaccines and protective efficacy in neonatal broiler chicks

The majority of infectious bursal disease virus (IBDV) strains circulating in the broiler chicken industry in Canada are variant strains (varIBDV). Despite high levels of maternally derived antibodies (MtAb), the circulating varIBDVs can establish infection and cause severe immunosuppression in broiler chicks. The objective of this study was to evaluate circulating varIBDVs as broiler breeder vaccine candidates and investigate their protective efficacy against varIBDV challenge in their progeny chicks. Six groups of breeders (20 females/group) were vaccinated with varIBDV strains, SK09, SK10, SK11, SK12, and SK13 or saline at the age of 13 weeks and antibody response was determined by ELISA at 3–7-, and 20- weeks post-vaccination. We also included commercial chicks for the comparison. Results showed that SK-09 is the most antigenic strain, followed by SK-10, SK-12, and SK-13. In contrast, SK-11 showed the lowest antibody response, and over time, antibody titers steadily decreased. Eggs from breeders were collected at 21-week post-vaccination and incubated to produce their respective progenies. The serum antibody titer in day-old chicks showed a successful MtAb transfer. Progeny chicks (n = 40/group) were orally challenged with varIBDV-SK-09 strain at 6 days of age and serum antibody titer (19 d and 35 d of age), bursa to body weight ratio (19 d and 35 d of age), bursal viral load (9 d and 19 d of age) was examined to assess the protection against IBDV. Following the challenge, we found a significant increase in the antibody titers in MtAb-free and commercial vaccine groups than in the varIBDV groups, both at 19 d and 35 d of age. The BBW ratio and viral load data indicated a significant homologous and heterologous protection against varIBDV-SK-09 challenge by SK-09 and SK-10 MtAbs, respectively. Overall, this study demonstrated the feasibility of developing breeder vaccines using circulating varIBDV as candidate vaccine antigens.     

Efficacy of recombinant Marek’s disease virus vectored vaccines with computationally optimized broadly reactive antigen (COBRA) hemagglutinin insert against genetically diverse H5 high pathogenicity avian influenza viruses

The genetic and antigenic drift associated with the high pathogenicity avian influenza (HPAI) viruses of Goose/Guangdong (Gs/GD) lineage and the emergence of vaccine-resistant field viruses underscores the need for a broadly protective H5 influenza A vaccine. Here, we tested experimental vector herpesvirus of turkey (vHVT)-H5 vaccines containing either wild-type clade 2.3.4.4A-derived H5 inserts or computationally optimized broadly reactive antigen (COBRA) inserts with challenge by homologous and genetically divergent H5 HPAI Gs/GD lineage viruses in chickens. Direct assessment of protection was confirmed for all the tested constructs, which provided clinical protection against the homologous and heterologous H5 HPAI Gs/GD challenge viruses and significantly decreased oropharyngeal shedding titers compared to the sham vaccine. The cross reactivity was assessed by hemagglutinin inhibition (HI) and focus reduction assay against a panel of phylogenetically and antigenically diverse H5 strains. The COBRA-derived H5 inserts elicited antibody responses against antigenically diverse strains, while the wild-type-derived H5 vaccines elicited protection mostly against close antigenically related clades 2.3.4.4A and 2.3.4.4D viruses. In conclusion, the HVT vector, a widely used replicating vaccine platform in poultry, with H5 insert provides clinical protection and significant reduction of viral shedding against homologous and heterologous challenge. In addition, the COBRA-derived inserts have the potential to be used against antigenically distinct co-circulating viruses and future drift variants.