Correlation between anthrax lethal toxin neutralizing antibody levels and survival in guinea pigs and nonhuman primates vaccinated with the AV7909 anthrax vaccine candidate

The anthrax vaccine candidate AV7909 is being developed as a next generation vaccine for a post-exposure prophylaxis (PEP) indication against anthrax. AV7909 consists of the Anthrax Vaccine Adsorbed (AVA, BioThrax®) bulk drug substance adjuvanted with the immunostimulatory oligodeoxynucleotide (ODN) compound, CPG 7909. The addition of CPG 7909 to AVA enhances both the magnitude and the kinetics of antibody responses in animals and human subjects, making AV7909 a suitable next-generation vaccine for use in a PEP setting. The studies described here provide initial information on AV7909-induced toxin-neutralizing antibody (TNA) levels associated with the protection of animals from lethal Bacillus anthracis challenge. Guinea pigs or nonhuman primates (NHPs) were immunized on Days 0 and 28 with various dilutions of AV7909, AVA or a saline or Alhydrogel + CPG 7909 control. Animals were challenged via the inhalational route with a lethal dose of aerosolized B. anthracis (Ames strain) spores and observed for clinical signs of disease and mortality. The relationship between pre-challenge serum TNA levels and survival following challenge was determined in order to calculate a threshold TNA level associated with protection. Immunisation with AV7909 induced a rapid, highly protective TNA response in guinea pigs and NHPs. Surprisingly, the TNA threshold associated with a 70% probability of survival for AV7909 immunized animals was substantially lower than the threshold which has been established for the licensed AVA vaccine. The results of this study suggest that the TNA threshold of protection against anthrax could be modified by the addition of an immune stimulant such as CPG 7909 and that the TNA levels associated with protection may be vaccine-specific.     

Replication-defective lymphocytic choriomeningitis virus vectors expressing guinea pig cytomegalovirus gB and pp65 homologs are protective against congenital guinea pig cytomegalovirus infection

BackgroundCongenital cytomegalovirus infection can be life-threatening and often results in significant developmental deficits and/or hearing loss. Thus, there is a critical need for an effective anti-CMV vaccine.ObjectiveTo determine the efficacy of replication-defective lymphocytic choriomeningitis virus (rLCMV) vectors expressing the guinea pig CMV (GPCMV) antigens, gB and pp65, in the guinea pig model of congenital CMV infection.MethodsFemale Hartley strain guinea pigs were divided into three groups: Buffer control group (n = 9), rLCMV-gB group (n = 11), and rLCMV-pp65 (n = 11). The vaccines were administered three times IM at 1.54 × 10⁶ FFU per dose at 21-day intervals. At two weeks after vaccination, the female guinea pigs underwent breeding. Pregnant guinea pigs were challenged SQ at ∼45–55 days of gestation with 1 × 10⁵ PFU of GPCMV. Viremia in the dams, pup survival, weights of pups at delivery, and viral load in both dam and pup tissues were determined.ResultsPup survival was significantly increased in the LCMV-gB vaccine group. There was 23% pup mortality in the gB vaccine group (p = 0.044) and 26% pup mortality in the pp65 vaccine group (p = 0.054) compared to 49% control pup mortality. The gB vaccine induced high levels of gB binding and detectable neutralizing antibodies, reduced dam viremia, and significantly reduced viral load in dam tissues compared to control dams (p < 0.03). Reduced viral load and transmission in pups born to gB-vaccinated dams was observed compared to pups from pp65-vaccinated or control dams.ConclusionsThe rLCMV-gB vaccine significantly improved pup survival and also increased pup weights and gestation time. The gB vaccine was also more effective at decreasing viral load in dams and pups and limiting congenital transmission. Thus, rLCMV vectors that express CMV antigens may be an effective vaccine strategy for congenital CMV infection.     

Development of a dual vaccine for prevention of Brucella abortus infection and Escherichia coli O157:H7 intestinal colonization

Zoonoses that affect human and animal health have an important economic impact. In the study now presented, a bivalent vaccine has been developed that has the potential for preventing the transmission from cattle to humans of two bacterial pathogens: Brucella abortus and Shiga toxin-producing Escherichia coli (STEC). A 66 kDa chimeric antigen, composed by EspA, Intimin, Tir, and H7 flagellin (EITH₇) from STEC, was constructed and expressed in B. abortus Δpgm vaccine strain (BabΔpgm). Mice orally immunized with BabΔpgm(EITH₇) elicited an immune response with the induction of anti-EITH₇ antibodies (IgA) that clears an intestinal infection of E. coli O157:H7 three times faster (t = 4 days) than mice immunized with BabΔpgm carrier strain (t = 12 days). As expected, mice immunized with BabΔpgm(EITH₇) strain also elicited a protective immune response against B. abortus infection. A Brucella-based vaccine platform is described capable of eliciting a combined protective immune response against two bacterial pathogens with diverse lifestyles—the intracellular pathogen B. abortus and the intestinal extracellular pathogen STEC.     

Cross-species prediction of human survival probabilities for accelerated anthrax vaccine absorbed (AVA) regimens and the potential for vaccine and antibiotic dose sparing

Anthrax vaccine adsorbed (AVA, BioThrax) was recently approved by the Food and Drug Administration (FDA) for a post-exposure prophylaxis (PEP) indication in adults 18–65 years of age. The schedule is three doses administered subcutaneous (SC) at 2-week intervals (0, 2, and 4 weeks), in conjunction with a 60-day course of antimicrobials. The Public Health Emergency Medical Countermeasures Enterprise (PHEMCE) developed an animal model to support assessment of a shortened antimicrobial PEP duration following Bacillus anthracis exposure. A nonhuman primate (NHP) study was completed to evaluate the efficacy of a two dose anthrax vaccine absorbed (AVA) schedule (0, 2 weeks) aerosol challenged with high levels of B. anthracis spores at week 4– the time point at which humans would receive the third vaccination of the approved PEP schedule. Here we use logistic regression models to combine the survival data from the NHP study along with serum anthrax lethal toxin neutralizing activity (TNA) and anti-PA IgG measured by enzyme linked immunosorbent assay (ELISA) data to perform a cross-species analysis to estimate survival probabilities in vaccinated human populations at this time interval (week 4 of the PEP schedule). The bridging analysis demonstrated that high levels of NHP protection also yield high predicted probability of human survival just 2 weeks after the second dose of vaccine with the full or half antigen dose regimen. The absolute difference in probability of human survival between the full and half antigen dose was estimated to be at most approximately 20%, indicating that more investigation of the half-antigen dose for vaccine dose sparing strategies may be warranted.     

Development of a DNA vaccine for chicken infectious anemia and its immunogenicity studies using high mobility group box 1 protein as a novel immunoadjuvant indicated induction of promising protective immune responses

Chicken infectious anaemia (CIA) is an economically important and emerging poultry disease reported worldwide. Current CIA vaccines have limitations like, the inability of the virus to grow to high titres in embryos/cell cultures, possession of residual pathogenicity and a risk of reversion to virulence. In the present study, a DNA vaccine, encoding chicken infectious anaemia virus (CIAV) VP1 and VP2 genes, was developed and co-administered with truncated chicken high mobility group box 1 (HMGB1ΔC) protein in young chicks for the evaluation of vaccine immune response. CIAV VP1 and VP2 genes were cloned in pTARGET while HMGB1ΔC in PET32b vector. In vitro expression of these gene constructs was evaluated by Western blotting. Further, recombinant HMGB1ΔC was evaluated for its biological activity. The CIAV DNA vaccine administration in specific pathogen free chicks resulted in moderately protective ELISA antibody titres in the range of 4322.87 ± 359.72 to 8288.19 ± 136.38, increased CD8⁺ cells, and a higher titre was observed by co-administration of novel adjuvant (HMGB1ΔC) and booster immunizations. The use of vaccine with adjuvant showed achieving antibody titres nearly 8500, titre considered as highly protective, which indicates that co-immunization of HMGB1ΔC may have a strong adjuvant activity on CIAV DNA vaccine induced immune responses. The able potential of HMGB1 protein holding strong adjuvant activity could be exploited further with trials with vaccines for other important pathogens for achieving the required protective immune responses.     

Safety and immunogenicity of Px563L,a recombinant anthrax vaccine candidate,in a two-dose regimen for post-exposure prophylaxis in healthy adults

Px563L is a next-generation anthrax vaccine candidate consisting of a protein subunit, mutant recombinant protective antigen SNKE167-ΔFF-315-E308D (mrPA), and liposome-embedded monophosphoryl lipid A (MPLA) adjuvant. Px563L has the potential to deliver an improved safety and immunogenicity profile relative to the currently licensed vaccine, which is produced from filtered B. anthracis culture supernatants.We conducted a Phase 1, double–blind, placebo–controlled, dose–escalation study in 54 healthy subjects to evaluate Px563L at 3 dose levels of mrPA (10, 50, and 80 mcg). For each dose level, 18 subjects were randomized in an 8:8:2 ratio to Px563L (mrPA with adjuvant), RPA563 (mrPA only) or placebo (saline). Each subject received an intramuscular (IM) injection on Day 0 and Day 28. Primary safety and immunogenicity analysis was conducted after all subjects completed the Day 70 visit, a duration deemed clinically relevant for post-exposure prophylaxis. Long-term safety was assessed through Day 393.Vaccinations with Px563L at all dose levels were well-tolerated. There were no serious adverse events or adverse events (AE) leading to early withdrawal. In all treatment groups, most AEs were due to injection site reactions, and all AEs at the 10 and 50 mcg dose levels were mild. For the primary immunogenicity endpoint (protective toxin neutralizing antibody 50% neutralization factor [TNA NF₅₀]), titers started to increase significantly after the second administration of Px563L, from Day 35 through Day 70, with the geometric mean and lower bound of the 95% confidence interval exceeding 0.56, a threshold correlating with significant survival in animal models of anthrax exposure.In conclusion, Px563L, administered as two IM doses 28 days apart, was well-tolerated and elicited a protective antibody response starting at seven days after the second vaccination. These findings support the continued development of Px563L in a two-dose regimen for anthrax post-exposure prophylaxis. ClinicalTrials.gov identifier NCT02655549.     

Evaluation of the protective efficacy of recombinant protective antigen vaccine (GC1109)-immunized human sera using passive immunization in a mouse model

The protective efficacy of human sera from vaccinated individuals with a new recombinant protective antigen anthrax vaccine (GC1109) against lethal spore challenge was evaluated in a mouse model. Eighteen human sera were selected from the vaccinated individuals based on their toxin neutralizing assay (TNA) titer (ED₅₀ of 55 to 668). The selected sera were diluted and passively transferred to A/J mice and the mice were subsequently challenged with 100 × LD₅₀ of Bacillus anthracis Sterne spores. The correlation between the survival rate of passively immunized mice and the TNA ED₅₀ of transferred sera was presented (r = 0.873, P-value < 0.001). The estimated TNA titer for 50% survival rate against lethal challenge was 197 (95% confidence interval of 149 and 260). The result suggest that GC1109 is protective against exposure to B. anthracis and the TNA titer of vaccinated serum can be an indicator for protective efficacy.     

Cross-protective efficacy of engineering serotype A foot-and-mouth disease virus vaccine against the two pandemic strains in swine

Foot-and-mouth disease (FMD) is a highly contagious vesicular disease that affects domestic and wild cloven-hoofed animals worldwide. Recently, a series of outbreaks of type A FMDV occurred in Southeast Asian countries, China, the Russia Federation, Mongolia, Kazakhstan and South Korea. The FMD virus (A/GDMM/CHA/2013) from China's Guangdong province (2013) is representative of those responsible for the latest epidemic, and has low amino acid identity (93.9%) in VP1 protein with the epidemic strain A/WH/CHA/09 from Wuhan, China in 2009. Both of isolates belong to the Sea-97 genotype of ASIA topotype. Therefore, the application of a new vaccine strain with cross-protective efficacy is of fundamental importance to control the spread of the two described pandemic strains. A chimeric strain rA/P1-FMDV constructed by our lab previously through replacing the P1 gene in the vaccine strain O/CHA/99 with that from the epidemic stain A/WH/CHA/09, has been demonstrated to exhibit good growth characteristics in culture, and the rA/P1-FMDV inactivated vaccine can provide protection against epidemic strain A/WH/CHA/09 in cattle. However, it is still unclear whether the vaccine produces efficient protection against the new pandemic strain (A/GDMM/CHA/2013). Here, vaccine matching and pig 50% protective dose (PD₅₀) tests were performed to assess the vaccine potency. The vaccine matching test showed cross-reactivity of sera from full dose vaccine vaccinated pigs with A/WH/CHA/09 and A/GDMM/CHA/2013 isolates, with average r₁ values of 0.94 ± 0.12 and 0.68 ± 0.06 (r₁ ≥ 0.3), which indicates that the rA/P1-FMDV vaccine is likely to confer good cross-protection against the two isolates. When challenged with two pandemic isolates A/WH/CHA/09 and A/GDMM/CHA/2013 strain, the vaccine achieved 12.51 PD₅₀ and 10.05 PD₅₀ per dose (2.8 μg), respectively. The results indicated that the rA/P1-FMDV inactivated vaccine could protect pigs against both A/WH/CHA/09 and A/GDMM/CHA/2013 pandemic isolates.     

Lethal factor antibodies contribute to lethal toxin neutralization in recipients of anthrax vaccine precipitated

A major difference between two currently licensed anthrax vaccines is presence (United Kingdom Anthrax Vaccine Precipitated, AVP) or absence (United States Anthrax Vaccine Adsorbed, AVA) of quantifiable amounts of the Lethal Toxin (LT) component Lethal Factor (LF). The primary immunogen in both vaccine formulations is Protective Antigen (PA), and LT-neutralizing antibodies directed to PA are an accepted correlate of vaccine efficacy; however, vaccination studies in animal models have demonstrated that LF antibodies can be protective. In this report we compared humoral immune responses in cohorts of AVP (n = 39) and AVA recipients (n = 78) matched 1:2 for number of vaccinations and time post-vaccination, and evaluated whether the LF response contributes to LT neutralization in human recipients of AVP. PA response rates (≥95%) and PA IgG concentrations were similar in both groups; however, AVP recipients exhibited higher LT neutralization ED₅₀ values (AVP: 1464.0 ± 214.7, AVA: 544.9 ± 83.2, p < 0.0001) and had higher rates of LF IgG positivity (95%) compared to matched AVA vaccinees (1%). Multiple regression analysis revealed that LF IgG makes an independent and additive contribution to the LT neutralization response in the AVP group. Affinity purified LF antibodies from two independent AVP recipients neutralized LT and bound to LF Domain 1, confirming contribution of LF antibodies to LT neutralization. This study documents the benefit of including an LF component to PA-based anthrax vaccines.     

The protective effect of a Schistosoma japonicum Chinese strain 23 kDa plasmid DNA vaccine in pigs is enhanced with IL-12

The schistosome integral membrane protein Sm/Sj23 was initially shown to induce protection in mice as a synthetic peptide vaccine and further, as a plasmid DNA vaccine to induce protection in mice, sheep and water buffalo. In this study we asked if we could induce protection against challenge infection in pigs against Schistosoma japonicum by vaccinating them with a plasmid DNA vaccine encoding the S. japonicum Chinese strain 23 kDa membrane protein. Further, we asked if we could enhance protective efficacy of this vaccine by the addition of IL-12. We compared vaccination with SjC23 plasmid DNA alone or with IL-12 plasmid DNA in pigs. Pigs were immunized three times at three weekly intervals. Thirty Chinese Songjang native pigs were divided into three groups. In group A, each pig was immunized with 500 μg of SjC23 plasmid DNA by intramuscular (i.m.) injection in both buttocks. In group B each pig was immunized with 500 μg of SjC23 plasmid DNA, and 500 μg of each of pcDNA3.1-p35 and 500 μg of pcDNA3.1-p40 DNA by i.m. injection. In group C each pig was immunized with 500 μg of pcDNA3.1 as the control. Thirty days post-vaccination, pigs were challenged with S. japonicum cercariae and adult and egg burdens and granuloma size determined 45 days post-challenge. The results showed that worm reduction rates in SjC23 group compared with control group were 29.2% and in the SjC23 + IL-12 group reduced 58.6%. Similarly the female worm reduction rates were 50.8 and 58.8%, the hepatic egg reduction rates were 48.2 and 56.4%, and the mean square measure reduction rates of hepatic egg granulomas were 48.6 and 44.4%, the mean diameter reduction rates of granulomas were 27.6 and 22.8% in pigs vaccinated with SjC23 or SjC23 + IL-12 compared to plasmid vaccinated pigs, respectively. Analysis of sera from pigs vaccinated with SjC23 showed that 4 of 10 pigs had anti-Sj23 antibody responses; with 5 of 10 pigs positive for anti-Sj23 in the SjC23+IL-12 group. These results suggest that vaccination with Sj23 DNA vaccine induces not only a significant reduction in worm and egg burdens, but also significantly reduces the size of egg granulomas, thus is also anti-pathology.     

Modeling maternal fetal RSV F vaccine induced antibody transfer in guinea pigs

BackgroundProtection of newborns and young infants against RSV disease via maternal immunization mediated by transplacental transfer of antibodies is under evaluation in third-trimester pregnant women with the RSV recombinant F nanoparticle vaccine (RSV F vaccine). Since the hemichorial placental architecture in guinea pigs and humans is similar, the guinea pig model was employed to assess RSV F vaccine immunogenicity in pregnant sows and to compare RSV-specific maternal antibody levels in their pups.MethodsThirty (30) presumptive pregnant guinea pigs were immunized on gestational day 25 and 46 with placebo (PBS), 30 μg RSV F, or 30 μg RSV F + 400 μg aluminum phosphate. Sera at delivery/birth (sows/pups) and 15 and 30 days post-partum (pups) were analyzed for the presence of anti-F IgG, palivizumab-competitive antibody (PCA) and RSV/A microneutralization (MN).ResultsThe rates of pregnancy and stillbirth were similar between controls and vaccinees. The vaccine induced high levels of anti-F IgG, PCA and MN in sows, with the highest levels observed in adjuvanted vaccinees. Placental transfer to pups was proportional to the maternal antibody levels, with concentration effects observed for all immune measures.ConclusionsThe RSV F vaccine was safe and immunogenic in pregnant guinea pigs and supported robust transplacental antibody transfer to their pups. Relative concentration of antibodies in the pups was observed even in the presence of high levels of maternal antibody. Guinea pigs may be an important safety and immunogenicity model for preclinical assessment of candidate vaccines for maternal immunization.     

Brucella abortus S19 and RB51 vaccine immunogenicity test: Evaluation of three mice (BALB/c,Swiss and CD-1®) and two challenge strains (544 and 2308)

The aim of the present study was to evaluate the use of different mouse strains (BALB/c, Swiss and CD-1^®) and different challenge strains (Brucella abortus 544 and 2308) in the study of B. abortus vaccine (S19 and RB51) immunogenicity test in the murine model. No significant difference in B. abortus vaccine potency assay was found with the use of B. abortus 544 or B. abortus 2308 as challenge strain. Results of variance analysis showed an interaction between treatment and mouse strain; therefore these parameters could not be compared separately. When CD-1^® groups were compared, those vaccinated showed significantly lower counts than non-vaccinated ones (P < 0.05), independently of the vaccine received (S19 or RB51). Similar results were observed on BALB/c groups. However, in Swiss mouse groups, S19 was more protective than RB51 (P  <0.05), which showed protection when compared to the non-vaccinated group (P < 0.05). In summary, data from the present study showed that CD-1^®, BALB/c and Swiss mice strains, as well as both challenge strains, B. abortus strains 544 and 2308, can be used in immunogenicity tests of S19 and RB51 vaccines.     

Preclinical identification of vaccine induced protective correlates in human leukocyte antigen expressing transgenic mice infected with Coccidioides posadasii

There is an emerging interest to develop human vaccines against medically-important fungal pathogens and a need for a preclinical animal model to assess vaccine efficacies and protective correlates. HLA-DR4 (DRB110401 allele) transgenic mice express a human major histocompatibility complex class II (MHC II) receptor in such a way that CD4⁺ T-cell response is solely restricted by this human molecule. In this study HLA-DR4 transgenic mice were immunized with a live-attenuated vaccine (ΔT) and challenged by the intranasal route with 50–70 Coccidioides posadasii spores, a potentially lethal dose. The same vaccination regimen offers 100% survival for C57BL/6 mice. Conversely, ΔT-vaccinated HLA-DR4 mice displayed 3 distinct manifestations of Coccidioides infection including 40% fatal acute (FAD), 30% disseminated (DD) and 30% pulmonary disease (PD). The latter 2 groups of mice had reduced loss of body weight and survived to at least 50 days postchallenge (dpc). These results suggest that ΔT vaccinated HLA-DR4 mice activated heterogeneous immunity against pulmonary Coccidioides infection. Vaccinated HLA-DR4 mice displayed early expansion of Th1 and Th17 cells and recruitment of inflammatory innate cells into Coccidioides-infected lungs during the first 9 dpc. While contraction rates of Th cells and the inflammatory response during 14–35 dpc significantly differed among the 3 groups of vaccinated HLA-DR4 mice. The FAD group displayed a sharply reduced Th1 and Th17 response, while overwhelmingly recruiting neutrophils into lungs during 9–14 days. The FAD group approached moribund by 14 dpc. In contrast, vaccinated HLA-DR4 survivors gradually contracted Th cells and inflammatory response with the greatest rate in the PD group. While vaccinated HLA-DR4 mice are susceptible to Coccidioides infection, they are useful for evaluation of vaccine efficacy and identification of immunological correlates against this mycosis.     

Development of a subunit vaccine containing recombinant Riemerella anatipestifer outer membrane protein A and CpG ODN adjuvant

Riemerella anatipestifer, a Gram-negative bacillus, causes septicemia that can result in high mortality for ducklings. In this study, we evaluated the immune response and protective efficacy provided by a subunit vaccine containing recombinant outer membrane protein A (rOmpA) and plasmid constructs containing CpG oligodeoxynucleotides (ODN). Results showed that CpG ODN enhanced both humoral and cell-mediated immunity elicited by rOmpA as early as two weeks after primary immunization. When compared to ducks immunized with rOmpA, ducks immunized with rOmpA + CpG ODN showed higher levels (p < 0.05) of antibody titer, T cell proliferation, and percentages of CD4⁺ and CD8⁺ T cell in peripheral blood mononuclear cells (PBMCs). The relative fold inductions of mRNA expression of Th1-type (IFN-γ and IL-12), and Th2-type (IL-6) cytokines in PBMCs isolated from ducks immunized with rOmpA + CpG ODN were significantly higher than those of the rOmpA group. Homologous challenge result showed that the rOmpA + CpG ODN vaccine reduced the pathological score by 90% in comparison with the saline control. In conclusion, our study found that CpG ODN can enhance both humoral and cellular immunity elicited by a rOmpA vaccine. The rOmpA + CpG ODN vaccine can be further developed as a subunit vaccine against R. anatipestifer.     

Regulated expression of virulence gene mviN provides protective immunity and colonization control of Salmonella in poultry

Current live attenuated vaccines for control of Salmonella in poultry persist in the ceca and may persist in the environment. In this paper we report the construction and characterization of the vaccine efficacy of a Salmonella mutant strain with inducible mviN expression and rapid clearance from the host. The mutant was effective in oral immunization of the broiler chicken host against a virulent Salmonella oral challenge strain, having a mean 7 × 10⁶ CFU/g in the ceca of unvaccinated controls compared to a mean 2 × 10³ CFU/g in the ceca of vaccinated chickens at 4 weeks post-challenge (6 weeks of age). The mutant strain also demonstrated immunogenicity, reduced organ colonization, and rapid clearance in broiler chickens within 3 weeks of inoculation.     

Efficacy and safety of high-dose influenza vaccine in elderly adults: A systematic review and meta-analysis

IntroductionOlder adults are prioritized for influenza vaccination but also have lowered antibody responses to the vaccine. Higher-doses of influenza antigen may increase immune response and thus be more effective. Our objectives were to compare the efficacy and safety of the high-dose influenza vaccine to the standard-dose influenza vaccine in the elderly (age > 65).MethodsData sources: Randomized trials (RCTs) from Medline (Ovid), EMBASE (Ovid), Cochrane Library (Wiley), ClinicalTrials.gov, reference lists of relevant articles, and gray literature.Study selection: Two reviewers independently identified RCTs comparing high-dose influenza vaccine (60 μg of hemagglutinin per strain) to standard-dose influenza vaccine (15 μg of hemagglutinin per strain) in adults over the age of 65 years.Data extraction: Two reviewers independently extracted trial-level data including population characteristics, interventions, outcomes, and funding sources. Risk of bias was assessed using the Cochrane Risk of Bias tool.ResultsWe included seven eligible trials; all were categorized as having a low (n = 3) or unclear (n = 4) risk of bias. Patients receiving the high-dose vaccine had significantly less risk of developing laboratory-confirmed influenza infections (Relative Risk 0.76, 95%CI 0.65 to 0.90; I² 0%, 2 trials, 41,141 patients). Post-vaccination geometric mean titres and seroprotection rates were also higher in high-dose vaccine recipients. There were no protocol-defined serious adverse events in the included trials in either group.ConclusionsIn elderly adults, the high-dose influenza vaccine was well-tolerated, more immunogenic, and more efficacious in preventing influenza infections than the standard-dose vaccine. Further pragmatic trials are needed to determine if the higher efficacy translates into higher vaccine effectiveness in adults over the age of 65.     

Adjuvant potential of resiquimod with inactivated Newcastle disease vaccine and its mechanism of action in chicken

Resiquimod (R-848), an imidazoquinoline compound, is a potent synthetic Toll-like receptor (TLR) 7 agonist. Although the solitary adjuvant potential of R-848 is well established in mammals, such reports are not available in avian species hitherto. Hence, the adjuvant potential of R-848 was tested in SPF chicken in this study. Two week old chicks were divided into four groups (10 birds/group) viz., control (A), inactivated Newcastle disease virus (NDV) vaccine prepared from velogenic strain (B), commercial oil adjuvanted inactivated NDV vaccine prepared from lentogenic strain (C) and inactivated NDV vaccine prepared from velogenic strain with R-848 (D). Booster was given two weeks post primary vaccination. Humoral immune response was assessed by haemagglutination inhibition (HI) test and ELISA while the cellular immune response was quantified by lymphocyte transformation test (LTT) and flow cytometry post-vaccination. Entire experiment was repeated twice to check the reproducibility. Highest HI titre was observed in group D at post booster weeks 1 and 2 that corresponds to mean log₂ HI titre of 6.4 ± 0.16 and 6.8 ± 0.13, respectively. The response was significantly higher than that of group B or C (P < 0.01). LTT stimulation index (P ≤ 0.01) as well as CD4⁺ and CD8⁺ cells in flow cytometry (P < 0.05) were significantly high and maximum in group D. Group D conferred complete protection against virulent NDV challenge, while it was only 80% in group B and C. To understand the effects of R-848, the kinetics of immune response genes in spleen were analyzed using quantitative real-time PCR after R-848 administration (50 μg/bird, i.m. route). Resiquimod significantly up-regulated the expression of IFN-α, IFN-β, IFN-γ, IL-1β, IL-4, iNOS and MHC-II genes (P < 0.01). In conclusion, the study demonstrated the adjuvant potential of R-848 when co-administered with inactivated NDV vaccine in SPF chicken which is likely due to the up-regulation of immune response genes.     

A novel gE-deleted pseudorabies virus (PRV) provides rapid and complete protection from lethal challenge with the PRV variant emerging in Bartha-K61-vaccinated swine population in China

The currently used Bartha-K61 strain is a very safe and effective vaccine against pseudorabies (PR) and has played a critical role in the control and eradication of PR worldwide. Since late 2011, however, PR reemerged among Bartha-K61-vaccinated pig population in many regions in China. Our previous studies demonstrated that the Bartha-K61 vaccine was unable to provide complete protection from the challenge with the PRV TJ strain (PRVTJ), a representative emerging PRV variant that was isolated from a Bartha-K61-immunized pig farm in Tianjin, China. Here, we generated a gE-deleted PRV, named as rPRVTJ-delgE, based on PRVTJ and evaluated its safety and immunogenicity in pigs. Our results showed that groups of piglets (n = 5) immunized with 10³, 10⁴ or 10⁵ TCID₅₀ rPRVTJ-delgE did not exhibit clinical signs following immunization and challenge and were protected clinically and virologically from the lethal challenge with PRVTJ as early as 1 week post-immunization, in contrast with the incomplete protection provided by the Bartha-K61 vaccine. These indicate that rPRVTJ-delgE is a promising candidate vaccine for updating Bartha-K61 for the control of the currently epidemic PR in China.     

Salmonella Enteritidis with double deletion in phoP fliC and a competitive exclusion culture elicit substantial additive protective effects against Salmonella exposure in newly hatched chicks

A live Salmonella Enteritidis vaccine (SE 147N ΔphoP fliC), able to express both a homologous intestinal colonisation-inhibition effect and a systemic invasion-inhibition effect, was tested for its potential to generate a postulated additive protective effect in case of combined application with a competitive exclusion (CE) culture against Salmonella exposure in very young chicks. Both, SE 147N ΔphoP fliC and the CE culture alone were highly protective against systemic and intestinal colonisation of the challenge strain in case of moderate Salmonella exposure, consequently, additive protective effects in combined use could not be detected. However, in case of high Salmonella Enteritidis challenge with 10⁶ cfu/bird at day 3 of life the combination of the ΔphoP fliC vaccine and the CE culture resulted in a protective effect much more pronounced than either of the single preparations and most substantial compared to untreated control birds. The term additive protective effects reflects the recognition that exclusion effects by gut flora cultures and inhibition effects by Salmonella vaccines are caused by different mechanisms.     

Bartha-k61 vaccine protects growing pigs against challenge with an emerging variant pseudorabies virus

Since late 2011, pseudorabies (PR) has resurfaced in many large pig farms, causing great economic loss for the swine industry in China. The PRV variant strain with high virulence and antigenic variation has been considered to be the main cause, and much attention has been focused on how to prevent and control the reoccurrence of this disease in China. In this study, two kinds of vaccination strategy were employed to evaluate the protective effects of Bartha-k61vaccine against both variant PRV (XJ5) and classical PRV (Ra) strain challenge. Humoral immunity response, clinical signs, survival rate, body weight, virus shedding and pathology were assessed in commercial pigs. The results showed that Bartha-k61vaccine, administered either once or twice, was effective against the PRV variant (XJ5) challenge, while no significant differences were observed between single and prime-boost vaccinated pigs. However, pigs vaccinated twice had better body weight gains than those vaccinated once, following challenge with the classical PRV strain (Ra) (p < 0.01). Therefore, the Bartha-k61 vaccine appears to be an effective vaccine to control the spread of PRV variants in China in the absence of new powerful candidate vaccines specific to these PRV strains.