Influenza virus: immunity and vaccination strategies. Comparison of the immune response to inactivated and live, attenuated influenza vaccines

Consumption of gold kiwifruit reduces severity and duration of selected upper respiratory tract infection symptoms and increases plasma vitamin C concentration in healthy older adults

In the elderly, immunosenescence and malnourishment can contribute to increased risk and severity of upper respiratory tract infections (URTI). Gold kiwifruit (Actinidia chinensis 'Hort16A') contains nutrients important for immune function and mitigation of symptoms of infection, including vitamins C and E, folate, polyphenols and carotenoids. The objective of the present study was to evaluate whether regular consumption of gold kiwifruit reduces symptoms of URTI in older people, and determine the effect it has on plasma antioxidants, and markers of oxidative stress, inflammation and immune function. A total of thirty-two community-dwelling people (≥65 years) participated in a randomised crossover study, consuming the equivalent of four kiwifruit or two bananas daily for 4 weeks, with treatments separated by a 4-week washout period. Participants completed the Wisconsin Upper Respiratory Symptom Survey-21 daily, and blood samples were collected at baseline and at the end of each treatment and washout period. Gold kiwifruit did not significantly reduce the overall incidence of URTI compared with banana, but significantly reduced the severity and duration of head congestion, and the duration of sore throat. Gold kiwifruit significantly increased plasma vitamin C, α-tocopherol and lutein/zeaxanthin concentrations, and erythrocyte folate concentrations, and significantly reduced plasma lipid peroxidation. No changes to innate immune function (natural killer cell activity, phagocytosis) or inflammation markers (high-sensitivity C-reactive protein, homocysteine) were detected. Consumption of gold kiwifruit enhanced the concentrations of several dietary plasma analytes, which may contribute to reduced duration and severity of selected URTI symptoms, offering a novel tool for reducing the burden of URTI in older individuals.

Vaccination with M2e-based multiple antigenic peptides: characterization of the B cell response and protection efficacy in inbred and outbred mice

Background

The extracellular domain of the influenza A virus protein matrix protein 2 (M2e) is remarkably conserved between various human isolates and thus is a viable target antigen for a universal influenza vaccine. With the goal of inducing protection in multiple mouse haplotypes, M2e-based multiple antigenic peptides (M2e-MAP) were synthesized to contain promiscuous T helper determinants from the Plasmodium falciparum circumsporozoite protein, the hepatitis B virus antigen and the influenza virus hemagglutinin. Here, we investigated the nature of the M2e-MAP-induced B cell response in terms of the distribution of antibody (Ab) secreting cells (ASCs) and Ab isotypes, and tested the protective efficacy in various mouse strains.

Methodology/Principal Findings

Immunization of BALB/c mice with M2e-MAPs together with potent adjuvants, CpG 1826 oligonucleotides (ODN) and cholera toxin (CT) elicited high M2e-specific serum Ab titers that protected mice against viral challenge. Subcutaneous (s.c.) and intranasal (i.n.) delivery of M2e-MAPs resulted in the induction of IgG in serum and airway secretions, however only i.n. immunization induced anti-M2e IgA ASCs locally in the lungs, correlating with M2-specific IgA in the bronchio-alveolar lavage (BAL). Interestingly, both routes of vaccination resulted in equal protection against viral challenge. Moreover, M2e-MAPs induced cross-reactive and protective responses to diverse M2e peptides and variant influenza viruses. However, in contrast to BALB/c mice, immunization of other inbred and outbred mouse strains did not induce protective Abs. This correlated with a defect in T cell but not B cell responsiveness to the M2e-MAPs.

Conclusion/Significance

Anti-M2e Abs induced by M2e-MAPs are highly cross-reactive and can mediate protection to variant viruses. Although synthetic MAPs are promising designs for vaccines, future constructs will need to be optimized for use in the genetically heterogeneous human population.

Evaluation of the seroprevalence of influenza A(H1N1) 2009 on a university campus: a cross-sectional study

BACKGROUND

Human infection with influenza A(H1N1) 2009 was first identified in the United States on 15 April 2009 and on 11 June 2009, WHO declared that the rapidly spreading swine-origin influenza virus constituted a global pandemic. We evaluated the seroprevalence of influenza A(H1N1) 2009 virus on a large public University campus, as well as disparities in demographic, symptomatic and vaccination characteristics of participants.

METHODS

Using a cross-sectional study design, sera was collected from volunteers and then tested for the presence of antibodies to the virus using a ≥ 1:40 dilution cut-off by hemagglutination inhibition assay. In conjunction, participants were asked to complete a questionnaire allowing us to estimate risk factors for infection in this population, as well as distinguish artificially derived antibodies from naturally derived antibodies.

RESULTS

300 total participants were recruited and tested. 158 (52.6%) tested positive for influenza A(H1N1) 2009 via hemagglutination inhibition assay using a ≥ 1:40 dilution cut-off. 86 people (54.4%) tested positive for H1N1 but did not report experiencing symptoms during the pandemic meeting the May 2010 CDC definition of influenza-like illness. Furthermore, of those individuals who reported that they had received the H1N1 vaccine, 16% did not test positive.

CONCLUSIONS

Overall, 52.7% of the total study population tested positive for influenza A(H1N1) 2009. 54.4% of those who tested positive for influenza A(H1N1) 2009 using the ≥ 1:40 dilution cut-off on the hemagglutination inhibition assay in this study population did not report experiencing symptoms during the pandemic meeting the May 2010 CDC definition of influenza-like illness. 16% of those who reported receiving the H1N1 vaccine did not test positive by HAI. We also found that vaccination coverage for H1N1 vaccine was poor among Blacks and Latinos, despite the fact that vaccine was readily available at no cost.

Vaccine design of hemagglutinin glycoprotein against influenza

Influenza viruses continue to cause annual epidemics and pose the threat of a deadly global pandemic. Vaccination has remained the best approach for prevention and control of influenza infection. However, current influenza vaccines are only effective against closely-matched circulating strains, and therefore must be updated and administered every year. In this review, we discuss recent developments in the search for better influenza vaccines, especially using the major virus surface glycoprotein hemagglutinins (HAs). Understanding how glycans on HAs affect the immune response and knowledge of how broadly neutralizing antibodies are induced will pave the way for a cross-protective influenza vaccine that does not require frequent updates or annual immunizations.

Mucosal immunoglobulins and B cells of teleost fish

As physical barriers that separate teleost fish from the external environment, mucosae are also active immunological sites that protect them against exposure to microbes and stressors. In mammals, the sites where antigens are sampled from mucosal surfaces and where stimulation of naïve T and B lymphocytes occurs are known as inductive sites and are constituted by mucosa-associated lymphoid tissue (MALT). According to anatomical location, the MALT in teleost fish is subdivided into gut-associated lymphoid tissue (GALT), skin-associated lymphoid tissue (SALT), and gill-associated lymphoid tissue (GIALT). All MALT contain a variety of leukocytes, including, but not limited to, T cells, B cells, plasma cells, macrophages and granulocytes. Secretory immunoglobulins are produced mainly by plasmablasts and plasma cells, and play key roles in the maintenance of mucosal homeostasis. Until recently, teleost fish B cells were thought to express only two classes of immunoglobulins, IgM and IgD, in which IgM was thought to be the only one responding to pathogens both in systemic and mucosal compartments. However, a third teleost immunoglobulin class, IgT/IgZ, was discovered in 2005, and it has recently been shown to behave as the prevalent immunoglobulin in gut mucosal immune responses. The purpose of this review is to summarise the current knowledge of mucosal immunoglobulins and B cells of fish MALT. Moreover, we attempt to integrate the existing knowledge on both basic and applied research findings on fish mucosal immune responses, with the goal to provide new directions that may facilitate the development of novel vaccination strategies that stimulate not only systemic, but also mucosal immunity.

Oral vaccination with inactivated influenza vaccine induces cross-protective immunity

Oral vaccination would provide an easy and safe measure to prevent infectious diseases by facilitating mass immunization. We investigated the feasibility of oral vaccination with inactivated whole influenza virus (A/PR8/34). Oral vaccination of mice induced high levels of serum IgG and IgA antibodies specific to the homologous virus (A/PR8) as well as cross reactive to heterologous (A/California/04/09) and heterosubtypic viruses (A/Philippines/2/82). IgG1 isotype antibodies were found to be induced at significantly higher levels than IgG2a antibodies. These antibodies induced by oral vaccination exhibited hemagglutination inhibition activities. High levels of both IgG and IgA antibodies were induced in vagina and lungs. Mucosal IgA antibodies were also elicited in other sites including saliva, urine, and fecal samples. Orally vaccinated mice were completely protected against challenge with homologous or heterologous viruses, and partially protected against heterosubtypic virus. Importantly, high recall antibody secreting cell (ASC) responses were induced in spleen, indicating the generation of memory B cells by oral vaccination. The present study therefore presents new findings of cross-reactive antibodies at systemic and diverse mucosal sites, recall antibody responses, and cross-protective efficacies by oral vaccination, thus supporting a proof-of-concept that oral delivery of vaccines can be developed as an effective vaccination route.

New insights in mucosal vaccine development

Mucosal surfaces are the major entrance for infectious pathogens and therefore mucosal immune responses serve as a first line of defence. Most current immunization procedures are obtained by parenteral injection and only few vaccines are administered by mucosal route, because of its low efficiency. However, targeting of mucosal compartments to induce protective immunity at both mucosal sites and systemic level represents a great challenge. Major efforts are made to develop new mucosal candidate vaccines by selecting appropriate antigens with high immunogenicity, designing new mucosal routes of administration and selecting immune-stimulatory adjuvant molecules. The aim of mucosal vaccines is to induce broad potent protective immunity by specific neutralizing antibodies at mucosal surfaces and by induction of cellular immunity. Moreover, an efficient mucosal vaccine would make immunization procedures easier and be better suited for mass administration. This review focuses on contemporary developments of mucosal vaccination approaches using different routes of administration.

Evaluation of immune responses to seasonal influenza vaccination in healthy volunteers in South Apulia, Italy: a pilot study

BACKGROUND

The aim of our pilot study is to investigate different components of the immune response to influenza vaccination in a group of healthy volunteers. We evaluated the cellular immune response (CD4(+) T lymphocytes) by flow cytometry. The humoral immune response was assessed by measuring the serum haemagglutination inhibition antibody response.

METHODS

Healthy adult donors (n = 18), were vaccinated with a commercially influenza virus vaccine (FLUARIX® GlaxoSmithKline S.p.a. Verona, Italy), peripheral blood was drawn the same day as influenza virus vaccination and one month later in order to enumerate the antigen-specific CD4(+) T lymphocytes. Hemagglutination inhibition assay was performed to enumerate the titer of neutralizing antibodies. Samples of nasal-pharyngeal secretions were taken by swabbing, from ILI (Influenza like Illness) subjects among the studied group, in order to verify influenza infections and eventually identify viruses using Real Time PCR.

RESULTS AND CONCLUSIONS

Parenteral influenza vaccination results in significant increase in the CD4(+) Th cell population after vaccination. The number of pre-vaccination CD4(+) T cells was 0.018 [the results are presented as number of percent fluorescent cells per 10 000 lymphocytes (fixed cells)], while there was a significantly higher number of CD4(+) Th cells one month after vaccination (statistical significance was set at the level of α = 0.01). Twenty-two percent of patients demonstrated protective antibody levels to influenza A H1/N1 serotype. None was diagnosed with influenza type A or B.

KEYWORDS

T cells; Flow cytometry; Influenza virus; Influenza vaccine.

Nebulized live-attenuated influenza vaccine provides protection in ferrets at a reduced dose

Live-attenuated influenza vaccine (LAIV) is delivered to vaccine recipients using a nasal spray syringe. LAIV delivered by this method is immunogenic at current doses; however, improvements in nasal delivery might allow for significant dose reduction. We investigated LAIV vaccination in ferrets using a high efficiency nebulizer designed for nasal delivery. LAIV nasal aerosol elicited high levels of serum neutralizing antibodies and protected ferrets from homologous virus challenge at conventional (10(7)TCID(50)) and significantly reduced (10(3)TCID(50)) doses. Aerosol LAIV also provided a significant level of subtype-specific cross-protection. These results demonstrate the dose-sparing potential of nebulizer-based nasal aerosol LAIV delivery.

Intranasal administration of a flagellin-adjuvanted inactivated influenza vaccine enhances mucosal immune responses to protect mice against lethal infection

The influenza virus, a mucosal pathogen that infects the respiratory tract, is a major global health issue. There have been attempts to mucosally administer inactivated influenza vaccines to induce both mucosal and systemic immune responses. However, mucosally administered inactivated influenza vaccine has low immunogenicity, which is partially due to the lack of an effective mucosal adjuvant. The development of a safe and effective mucosal adjuvant is a prerequisite to the practical use of a mucosal inactivated influenza vaccine. We have previously demonstrated that a bacterial flagellin, Vibrio vulnificus FlaB, when mixed with antigen and administered intranasally, exerts a strong mucosal adjuvant activity by stimulating the Toll-like receptor 5 (TLR5). In this study, we tested whether the FlaB protein could serve as an effective mucosal adjuvant for an inactivated trivalent influenza vaccine (TIV) manufactured for humans; in a murine vaccination model, this vaccine consists of A/Brisbane/59/07 (H1N1 subtype), A/Uruguay/716/07 (H3N2 subtype), and B/Florida/4/06 (B type). Intranasal co-administration of the TIV with FlaB induced prominent humoral responses as demonstrated by high influenza-specific IgA levels in both the mucosal secretions and serum and significant specific IgG induction in the systemic compartment. The FlaB protein significantly potentiated influenza-specific cytokine production by draining lymph node cells and splenocytes. The FlaB mucosal adjuvant conferred excellent protection against a lethal challenge with a live virulent virus with high hemagglutination inhibition (HAI) antibody (Ab) titers. The FlaB did not accumulate in the olfactory nerve and epithelium, guaranteeing against a retrograde uptake into the central nervous system. These results suggest that FlaB can be used as a promising mucosal adjuvant for nasal inactivated influenza vaccine development.

Virus aggregating peptide enhances the cell-mediated response to influenza virus vaccine

Given the poor immunogenicity of current H5N1 influenza vaccines, additives and adjuvants remain a viable solution for increasing efficacy. Here, we demonstrate that a 20-amino acid peptide (EB) possessing influenza antiviral activity also enhances the immune response to H5N1 vaccination in mice. The addition of EB to formalin-inactivated whole-virus vaccine induced virion aggregation and these aggregates were readily engulfed by phagocytic cells in vitro. In vivo, mice vaccinated with a suboptimal dose of inactivated vaccine containing EB peptide had reduced morbidity, improved viral clearance, and faster recovery than mice receiving vaccine alone. This phenomenon was not accompanied by an increase in virus-specific antibodies. Instead, cell-mediated immunity was enhanced as demonstrated by increased interferon-γ production from splenocytes. This data demonstrates that the EB peptide may a useful adjuvant for boosting the efficacy of poorly immunogenic influenza vaccines.

Comparative immunogenicity and cross-clade protective efficacy of mammalian cell-grown inactivated and live attenuated H5N1 reassortant vaccines in ferrets

Continued H5N1 virus infection in humans highlights the need for vaccine strategies that provide cross-clade protection against this rapidly evolving virus. We report a comparative evaluation in ferrets of the immunogenicity and cross-protective efficacy of isogenic mammalian cell-grown, live attenuated influenza vaccine (LAIV) and adjuvanted, whole-virus, inactivated influenza vaccine (IIV), produced from a clade 1 H5N1 6:2 reassortant vaccine candidate (caVN1203-Len17rg) based on the cold-adapted A/Leningrad/134/17/57 (H2N2) master donor virus. Two doses of LAIV or IIV provided complete protection against lethal homologous H5N1 virus challenge and a reduction in virus shedding and disease severity after heterologous clade 2.2.1 H5N1 virus challenge and increased virus-specific serum and nasal wash antibody levels. Although both vaccines demonstrated cross-protective efficacy, LAIV induced higher levels of nasal wash IgA and reduction of heterologous virus shedding, compared with IIV. Thus, enhanced respiratory tract antibody responses elicited by LAIV were associated with improved cross-clade protection.

Evaluation of the immune benefits of two probiotic strains Bifidobacterium animalis ssp. lactis, BB-12® and Lactobacillus paracasei ssp. paracasei, L. casei 431® in an influenza vaccination model: a randomised, double-blind, placebo-controlled study

The present study investigated the ability of Bifidobacterium animalis ssp. lactis (BB-12®) and Lactobacillus paracasei ssp. paracasei (L. casei 431®) to modulate the immune system using a vaccination model in healthy subjects. A randomised, double-blind, placebo-controlled, parallel-group study was conducted in 211 subjects (56 % females, mean age 33·2 (sd 13·1) years). Subjects consumed a minimum of 10⁹ colony-forming units of BB-12® (capsule) or L. casei 431® (dairy drink) or a matching placebo once daily for 6 weeks. After 2 weeks, a seasonal influenza vaccination was given. Plasma and saliva samples were collected at baseline and after 6 weeks for the analysis of antibodies, cytokines and innate immune parameters. Changes from baseline in vaccine-specific plasma IgG, IgG1 and IgG3 were significantly greater in both probiotic groups v. the corresponding placebo group (L. casei 431®, P = 0·01 for IgG; P < 0·001 for remaining comparisons). The number of subjects obtaining a substantial increase in specific IgG (defined as ≥ 2-fold above baseline) was significantly greater in both probiotic groups v. placebo (BB-12®, P < 0·001 for IgG, IgG1 and IgG3; L. casei 431®, P < 0·001 for IgG1 and IgG3). Significantly greater mean fold increases for vaccine-specific secretory IgA in saliva were observed in both probiotic groups v. placebo (BB-12®, P = 0·017; L. casei 431®, P = 0·035). Similar results were observed for total antibody concentrations. No differences were found for plasma cytokines or innate immune parameters. Data herein show that supplementation with BB-12® or L. casei 431® may be an effective means to improve immune function by augmenting systemic and mucosal immune responses to challenge.

Universal peptide vaccines - optimal peptide vaccine design based on viral sequence conservation

Rapidly mutating viruses such as the hepatitis C virus (HCV), the human immunodeficiency virus (HIV), or influenza viruses (Flu) call for highly effective universal peptide vaccines, i.e. vaccines that do not only yield broad population coverage but also broad coverage of various viral strains. The efficacy of such vaccines is determined by multiple properties of the epitopes they comprise. Beyond the specific properties of each epitope, properties of the corresponding source antigens are of great importance. If a response is mounted against viral proteins with a low copy number within the cell or against proteins expressed very late, this response may fail to induce lysis of the infected cells before budding can take place. We here propose a novel methodology to optimize the epitope composition and assembly in order to induce maximum protection. In order for a peptide vaccine to yield the best possible universal protection, several conditions should be met: (a) an optimal choice of target antigens, (b) an optimal choice of highly conserved epitopes, (c) maximum coverage of the target population, and (d) the proper ordering of the epitopes in the final vaccine to ensure favorable cleavage. We propose a mathematical formalism for epitope selection and ordering that balances the constraints imposed by these different conditions. Focusing on HCV, HIV, and Flu, we show that not all of the conditions can be satisfied for all viruses. Depending on the virus, different constraints are harder to fulfill: for Flu, the conservation constraint is violated first, while for HIV, it is difficult to focus the response at the optimal target antigens. The proposed methodology can be applied to any virus to assess the feasibility of optimally combining the above-mentioned constraints.

CAF01 potentiates immune responses and efficacy of an inactivated influenza vaccine in ferrets

Trivalent inactivated vaccines (TIV) against influenza are given to 350 million people every year. Most of these are non-adjuvanted vaccines whose immunogenicity and protective efficacy are considered suboptimal. Commercially available non-adjuvanted TIV are known to elicit mainly a humoral immune response, whereas the induction of cell-mediated immune responses is negligible. Recently, a cationic liposomal adjuvant (dimethyldioctadecylammonium/trehalose 6,6'-dibehenate, CAF01) was developed. CAF01 has proven to enhance both humoral and cell-mediated immune responses to a number of different experimental vaccine candidates. In this study, we compared the immune responses in ferrets to a commercially available TIV with the responses to the same vaccine mixed with the CAF01 adjuvant. Two recently circulating H1N1 viruses were used as challenge to test the vaccine efficacy. CAF01 improved the immunogenicity of the vaccine, with increased influenza-specific IgA and IgG levels. Additionally, CAF01 promoted cellular-mediated immunity as indicated by interferon-gamma expressing lymphocytes, measured by flow cytometry. CAF01 also enhanced the protection conferred by the vaccine by reducing the viral load measured in nasal washes by RT-PCR. Finally, CAF01 allowed for dose-reduction and led to higher levels of protection compared to TIV adjuvanted with a squalene emulsion. The data obtained in this human-relevant challenge model supports the potential of CAF01 in future influenza vaccines.

Cytokines: the future of intranasal vaccine adjuvants

Due to its potential as an effective, needle-free route of immunization for use with subunit vaccines, nasal immunization continues to be evaluated as a route of immunization in both research and clinical studies. However, as with other vaccination routes, subunit vaccines often require the addition of adjuvants to induce potent immune responses. Unfortunately, many commonly used experimental vaccine adjuvants, such as cholera toxin and E. coli heat-labile toxin, are too toxic for use in humans. Because new adjuvants are needed, cytokines have been evaluated for their ability to provide effective adjuvant activity when delivered by the nasal route in both animal models and in limited human studies. It is the purpose of this paper to discuss the potential of cytokines as nasal vaccine adjuvants.

Limited efficacy of inactivated influenza vaccine in elderly individuals is associated with decreased production of vaccine-specific antibodies

During seasonal influenza epidemics, disease burden is shouldered predominantly by the very young and the elderly. Elderly individuals are particularly affected, in part because vaccine efficacy wanes with age. This has been linked to a reduced ability to induce a robust serum antibody response. Here, we show that this is due to reduced quantities of vaccine-specific antibodies, rather than a lack of antibody avidity or affinity. We measured levels of vaccine-specific plasmablasts by ELISPOT 1 week after immunization of young and elderly adults with inactivated seasonal influenza vaccine. Plasmablast-derived polyclonal antibodies (PPAbs) were generated from bulk-cultured B cells, while recombinant monoclonal antibodies (re-mAbs) were produced from single plasmablasts. The frequency of vaccine-specific plasmablasts and the concentration of PPAbs were lower in the elderly than in young adults, whereas the yields of secreted IgG per plasmablast were not different. Differences were not detected in the overall vaccine-specific avidity or affinity of PPAbs and re-mAbs between the 2 age groups. In contrast, reactivity of the antibodies induced by the inactivated seasonal influenza vaccine toward the 2009 pandemic H1N1 virus, which was not present in the vaccine, was higher in the elderly than in the young. These results indicate that the inferior antibody response to influenza vaccination in the elderly is primarily due to reduced quantities of vaccine-specific antibodies. They also suggest that exposure history affects the cross-reactivity of vaccination-induced antibodies.

Influenza vaccine responses in older adults

The most profound consequences of immune senescence with respect to public health are the increased susceptibility to influenza and loss of efficacy of the current split-virus influenza vaccines in older adults, which are otherwise very effective in younger populations. Influenza infection is associated with high rates of complicated illness including pneumonia, heart attacks and strokes in the 65+ population. Changes in both innate and adaptive immune function not only converge in the reduced response to vaccination and protection against influenza, but present significant challenges to new vaccine development. In older adults, the goal of vaccination is more realistically targeted to providing clinical protection against disease rather sterilizing immunity. Correlates of clinical protection may not be measured using standard techniques such as antibody titres to predict vaccine efficacy. Further, antibody responses to vaccination as a correlate of protection may fail to detect important changes in cellular immunity and enhanced vaccine-mediated protection against influenza illness in older people. This article will discuss the impact of influenza in older adults, immunologic targets for improved efficacy of the vaccines, and alternative correlates of clinical protection against influenza that are needed for more effective translation of novel vaccination strategies to improved protection against influenza in older adults.

Intramuscular immunization of mice with live influenza virus is more immunogenic and offers greater protection than immunization with inactivated virus

BACKGROUND

Influenza virus continues to cause significant hospitalization rates in infants and young children. A 2-dose regime of trivalent inactivated vaccine is required to generate protective levels of hemagglutination inhibiting (HAI) antibodies. A vaccine preparation with enhanced immunogenicity is therefore desirable.

METHODS

Mice were inoculated intramuscularly (IM) with live and inactivated preparations of A/Wisconsin/67/2005 (H3N2). Serum cytokine levels, hemagglutinin (HA)-specific antibody responses and nucleoprotein (NP)-specific CD8+ T cell responses were compared between vaccinated groups, as well as to responses measured after intranasal infection. The protective efficacy of each vaccine type was compared by measuring virus titers in the lungs and weight loss of mice challenged intranasally with a heterosubtypic virus, A/PR/8/34 (H1N1).

RESULTS

Intramuscular administration of live virus resulted in greater amounts of IFN-α, IL-12 and IFN-γ, HA-specific antibodies, and virus-specific CD8+ T cells, than IM immunization with inactivated virus. These increases corresponded with the live virus vaccinated group having significantly less weight loss and less virus in the lungs on day 7 following challenge with a sublethal dose of a heterosubtypic virus.

CONCLUSIONS

Inflammatory cytokines, antibody titers to HA and CD8+ T cell responses were greater to live than inactivated virus delivered IM. These increased responses correlated with greater protection against heterosubtypic virus challenge, suggesting that intramuscular immunization with live influenza virus may be a practical means to increase vaccine immunogenicity and to broaden protection in pediatric populations.

Field effectiveness of pandemic and 2009-2010 seasonal vaccines against 2009-2010 A(H1N1) influenza: estimations from surveillance data in France

BACKGROUND

In this study, we assess how effective pandemic and trivalent 2009-2010 seasonal vaccines were in preventing influenza-like illness (ILI) during the 2009 A(H1N1) pandemic in France. We also compare vaccine effectiveness against ILI versus laboratory-confirmed pandemic A(H1N1) influenza, and assess the possible bias caused by using non-specific endpoints and observational data.

METHODOLOGY AND PRINCIPAL FINDINGS

We estimated vaccine effectiveness by using the following formula: VE  =  (PPV-PCV)/(PPV(1-PCV)) × 100%, where PPV is the proportion vaccinated in the population and PCV the proportion of vaccinated influenza cases. People were considered vaccinated three weeks after receiving a dose of vaccine. ILI and pandemic A(H1N1) laboratory-confirmed cases were obtained from two surveillance networks of general practitioners. During the epidemic, 99.7% of influenza isolates were pandemic A(H1N1). Pandemic and seasonal vaccine uptakes in the population were obtained from the National Health Insurance database and by telephonic surveys, respectively. Effectiveness estimates were adjusted by age and week. The presence of residual biases was explored by calculating vaccine effectiveness after the influenza period. The effectiveness of pandemic vaccines in preventing ILI was 52% (95% confidence interval: 30-69) during the pandemic and 33% (4-55) after. It was 86% (56-98) against confirmed influenza. The effectiveness of seasonal vaccines against ILI was 61% (56-66) during the pandemic and 19% (-10-41) after. It was 60% (41-74) against confirmed influenza.

CONCLUSIONS

The effectiveness of pandemic vaccines in preventing confirmed pandemic A(H1N1) influenza on the field was high, consistently with published findings. It was significantly lower against ILI. This is unsurprising since not all ILI cases are caused by influenza. Trivalent 2009-2010 seasonal vaccines had a statistically significant effectiveness in preventing ILI and confirmed pandemic influenza, but were not better in preventing confirmed pandemic influenza than in preventing ILI. This lack of difference might be indicative of selection bias.

Immune responses in Atlantic salmon (Salmo salar) following protective vaccination against infectious salmon anemia (ISA) and subsequent ISA virus infection

Infectious salmon anemia (ISA) is an orthomyxoviral disease that has had devastating effects on farmed Atlantic salmon. ISA is still a disease resulting in continued loss of revenues and therefore development of effective vaccines is of great importance. Commercial vaccines against ISA are available, but the efficacy is poorly described. There is little information about vaccine-induced immune factors preventing ISA virus (ISAV) infection today. In this study we assessed the protective effects and immunogenicity of vaccines containing three different quantities of the inactivated ISAV antigen. Our findings indicated that immunization induced effective protection in Atlantic salmon with a relative percent survival (RPS) as high as 86. The level of protection was correlated to the amount of ISAV antigen in the vaccine, and fish immunized with high antigen amounts produced detectable ISAV-specific and neutralizing antibodies. While ISAV infection was detectable in non-vaccinated control fish challenged by cohabitation, no infection was detected in fish immunized with high antigen amounts. After challenge, transcriptional analysis of selected immune-related genes demonstrated activation of innate immune responses in ISAV-infected control fish, but not in vaccine protected fish. This study furthers the knowledge about vaccine efficacy and vaccine-induced immunity to ISAV challenge in Atlantic salmon.

Explaining rapid reinfections in multiple-wave influenza outbreaks: Tristan da Cunha 1971 epidemic as a case study

Influenza usually spreads through the human population in multiple-wave outbreaks. Successive reinfection of individuals over a short time interval has been explicitly reported during past pandemics. However, the causes of rapid reinfection and the role of reinfection in driving multiple-wave outbreaks remain poorly understood. To investigate these issues, we focus on a two-wave influenza A/H3N2 epidemic that occurred on the remote island of Tristan da Cunha in 1971. Over 59 days, 273 (96%) of 284 islanders experienced at least one attack and 92 (32%) experienced two attacks. We formulate six mathematical models invoking a variety of antigenic and immunological reinfection mechanisms. Using a maximum-likelihood analysis to confront model predictions with the reported incidence time series, we demonstrate that only two mechanisms can be retained: some hosts with either a delayed or deficient humoral immune response to the primary influenza infection were reinfected by the same strain, thus initiating the second epidemic wave. Both mechanisms are supported by previous empirical studies and may arise from a combination of genetic and ecological causes. We advocate that a better understanding and account of heterogeneity in the human immune response are essential to analysis of multiple-wave influenza outbreaks and pandemic planning.

Intranasal delivery of whole cell lysate of Mycobacterium tuberculosis induces protective immune responses to a modified live porcine reproductive and respiratory syndrome virus vaccine in pigs

Porcine reproductive and respiratory syndrome (PRRS) is an economically important disease to pork producers worldwide. Commercially, both live and killed PRRSV vaccines are available to control PRRS, but they are not always successful. Based on the results of mucosal immunization studies in other viral models, a good mucosal vaccine may be an effective way to elicit protective immunity to control PRRS outbreaks. In the present study, mucosal adjuvanticity of Mycobacterium tuberculosis whole cell lysate (Mtb WCL) was evaluated in pigs administered a modified live PRRS virus vaccine (PRRS-MLV) intranasally. A Mtb WCL mediated increase in the frequency of NK cells, CD8(+)and CD4(+) T cells, and γδ T cells in pig lungs were detected. Importantly, an increased and early generation of PRRSV specific neutralizing antibodies were detected in PRRS-MLV+ Mtb WCL compared to pigs inoculated with vaccine alone. In addition, there was an increased secretion of Th1 cytokines (IFNγ and IL-12) that correlated with a reciprocal reduction in the production of immunosuppressive cytokines (IL-10 and TGFβ) as well as T-regulatory cells in pigs vaccinated with PRRS-MLV+ Mtb WCL. Further, a complete rescue in arginase levels in the lungs mediated through Mtb WCL was observed in pigs inoculated with PRRS-MLV. In conclusion, Mtb WCL may be a potent mucosal adjuvant for PRRS-MLV in order to potentiate the anti-PRRSV specific immune responses to control PRRS effectively.

Identification of the minimal active sequence of an anti-influenza virus peptide

The antiviral peptide, entry blocker (EB), inhibits influenza virus replication by preventing attachment to cells. Here, we identified the minimal and optimal EB sequence that retained antiviral activity with a 50% inhibitory concentration (IC(50)) and 50% effective concentration (EC(50)) similar to those of the full-length EB peptide and several truncated variants that possessed up to 10-fold lower IC(50)s. These data have implications for improving the antiviral efficacy of EB-derived peptides while decreasing production costs and easing synthesis.

Long term persistence of IgE anti-influenza virus antibodies in pediatric and adult serum post vaccination with influenza virus vaccine

The production of IgE specific to different viruses (HIV-1, Parvovirus B19, Parainfluenza virus, Varicella Zoster Virus), and the ability of IgE anti-HIV-1 to suppress HIV-1 production in vitro, strongly suggest an important role for IgE and/or anti viral specific IgE in viral pathogenesis. Nevertheless, the presence and persistence of IgE anti-Influenza virus antibodies has not been studied. Total serum IgE and specific IgE and IgG anti-Influenza virus antibodies were studied in children (N = 3) (m/f 14-16 y/o) and adults (N = 3) (m/f, 41-49 y/o) 2-20 months after vaccination with Influenza virus (Flumist(®) or Fluzone(®)), as well as in non-vaccinated children (N = 2). (UniCAP total IgE Fluoroenzymeimmunoassay, ELISA, Immunoblot). We found that serum of vaccinated children and adults contained IgE and IgG anti-Influenza virus antibodies approaching two years post vaccination. Non-vaccinated children did not make either IgE or IgG anti-Influenza antibodies. Similar levels of IL-2, IFN-γ, IL-4, and IL-10 cytokines were detected in serum of vaccinated compared with non vaccinated subjects (p > 0.05), as well as between vaccinated adults compared with vaccinated children and non vaccinated subjects (p > 0.05). Vaccinated children and adults continue to produce IgE anti-Influenza virus antibodies long term post vaccination. The long term production of IgE anti-Influenza virus antibodies induced by vaccination may contribute to protective immunity against Influenza.

Human influenza vaccines and assessment of immunogenicity

Influenza is responsible for the infection of approximately 20% of the population every season and for an annual death toll of approximately half a million people. The most effective means for controlling infection and thereby reducing morbidity and mortality is vaccination by injection with an inactivated vaccine, or by intranasal administration of a live-attenuated vaccine. Protection is not always optimal and there is a need for the development of new vaccines with improved efficacy and for the expansion of enrollment into vaccination programs. An overview of old and new vaccines is presented. Methods of monitoring immune responses such as hemagglutination-inhibition, ELISA and neutralization tests are evaluated for their accuracy in the assessment of current and new-generation vaccines.

Genetic bases of the temperature-sensitive phenotype of a master donor virus used in live attenuated influenza vaccines: A/Leningrad/134/17/57 (H2N2)

Trivalent live attenuated influenza vaccines whose type A components are based on cold-adapted A/Leningrad/134/17/57 (H2N2) (caLen17) master donor virus (MDV) have been successfully used in Russia for decades to control influenza. The vaccine virus comprises hemagglutinin and neuraminidase genes from the circulating viruses and the remaining six genes from the MDV. The latter confer temperature-sensitive (ts) and attenuated (att) phenotypes. The ts phenotype of the vaccine virus is a critical biological determinant of attenuation of virulence. We developed a plasmid-based reverse genetics system for MDV caLen17 to study the genetic basis of its ts phenotype. Mutations in the polymerase proteins PB1 and PB2 played a crucial role in the ts phenotype of MDV caLen17. In addition, we show that caLen17-specific ts mutations could impart the ts phenotype to the divergent PR8 virus, suggesting the feasibility of transferring the ts phenotype to new viruses of interest for vaccine development.

Stressor-induced alterations of adaptive immunity to vaccination and viral pathogens

The stress response influences the immune system, and studies in laboratory animals indicate that the response to stress significantly reduces resistance to infectious challenge. Only a few studies, however, have determined the impact of the stress response on human susceptibility to infectious challenge due, in part, to the difficulties of using live, replicating pathogens in human research. As a result, many studies have assessed the immune response to vaccination as a surrogate for the immune response to an infectious challenge. Thus, much is known about how the stress response influences adaptive immunity, and memory responses, to vaccination. These studies have yielded data concerning the interactions of the nervous and immune systems and have provided important information for clinicians administering vaccines to susceptible populations. This review provides a brief overview of the immune response to commonly used vaccines and the impact that stress can have on vaccine-specific immunity.

Mucosal targeting of a BoNT/A subunit vaccine adjuvanted with a mast cell activator enhances induction of BoNT/A neutralizing antibodies in rabbits

BACKGROUND

We previously reported that the immunogenicity of Hcβtre, a botulinum neurotoxin A (BoNT/A) immunogen, was enhanced by fusion to an epithelial cell binding domain, Ad2F, when nasally delivered to mice with cholera toxin (CT). This study was performed to determine if Ad2F would enhance the nasal immunogenicity of Hcβtre in rabbits, an animal model with a nasal cavity anatomy similar to humans. Since CT is not safe for human use, we also tested the adjuvant activity of compound 48/80 (C48/80), a mast cell activating compound previously determined to safely exhibit nasal adjuvant activity in mice.

METHODS

New Zealand White or Dutch Belted rabbits were nasally immunized with Hcβtre or Hcβtre-Ad2F alone or combined with CT or C48/80, and serum samples were tested for the presence of Hcβtre-specific binding (ELISA) or BoNT/A neutralizing antibodies.

RESULTS

Hcβtre-Ad2F nasally administered with CT induced serum anti-Hcβtre IgG ELISA and BoNT/A neutralizing antibody titers greater than those induced by Hcβtre + CT. C48/80 provided significant nasal adjuvant activity and induced BoNT/A-neutralizing antibodies similar to those induced by CT.

CONCLUSIONS

Ad2F enhanced the nasal immunogenicity of Hcβtre, and the mast cell activator C48/80 was an effective adjuvant for nasal immunization in rabbits, an animal model with a nasal cavity anatomy similar to that in humans.

Plasmablast-derived polyclonal antibody response after influenza vaccination

Conventional measurement of antibody responses to vaccines largely relies on serum antibodies, which are primarily produced by bone marrow plasma cells and may not represent the entire vaccine-induced B cell repertoire, including important functional components such as those targeted to mucosal sites. After immunization or infection, activated B cells differentiate into plasmablasts in local lymphoid organs, then traffic through circulation to the target sites where they further develop into plasma cells. On day 7 after influenza vaccination, a burst of plasmablasts, highly enriched for vaccine-specific antibody secreting cells, appears in the peripheral blood. This provides a unique window to the overall B cell response to the vaccine, without interference of pre-existing cross-reactive serum antibody. In this study we isolated B cells from volunteers on day 7 after immunization with the inactivated influenza vaccine and cultured them ex vivo to collect plasmablast-derived polyclonal antibodies (PPAb). The PPAb contained secreted IgG and IgA, which was approximately 0.2ng per antibody secreting cell. Influenza-specific IgG and IgA binding activity was detected in PPAb at dilutions up to 10(5) by ELISA. The ratio of the titers of influenza-specific IgA to IgG by ELISA was 4-fold higher in PPAb than in day 28 post-vaccination sera, suggesting that vaccine-induced IgA is enriched in PPAb compared to sera. Functional activity was also detected in PPAb as determined by microneutralization and hemagglutination inhibition assays. In addition to bulk B cell cultures, we also cultured plasmablast subsets sorted by cell surface markers to generate PPAb. These results suggest that PPAb better reflects the mucosal IgA response than serum samples. Since PPAb are exclusively produced by recently activated B cells, it allows assessing vaccine-induced antibody response without interference from pre-existing cross-reactive serum antibodies and permits an assessment of antibody avidity based on antigen specific binding and antibody quantity. Therefore this assay is particularly useful for studying vaccine/infection-induced antibodies against antigens that might have previously circulated, such as antibody responses to rotavirus, dengue or influenza viruses in which cross-reactive antibodies against different virus serotypes/subtypes play a critical role in immunity and/or pathogenesis.

The relative efficacy of trivalent live attenuated and inactivated influenza vaccines in children and adults

Please cite this paper as: Ambrose CS et al. (2011) The relative efficacy of trivalent live attenuated and inactivated influenza vaccines in children and adults. Influenza and Other Respiratory Viruses 5(2), 67–75.

In the United States, two types of vaccines are recommended for the prevention of influenza: an intranasal live attenuated influenza vaccine (LAIV) for eligible individuals aged 2–49 years and unadjuvanted injectable trivalent inactivated vaccines (TIV) for eligible individuals aged ≥6 months. Several recent studies have compared the efficacy of the 2 vaccines in children and adults. In children 6 months to 18 years of age, each of the four comparative studies of LAIV and TIV demonstrated that LAIV was more protective. In individuals 17–49 years of age, most comparative studies have demonstrated that LAIV and TIV were similarly efficacious or that TIV was more efficacious. However, LAIV was shown to be more protective than TIV in new military recruits of all ages, and placebo‐controlled studies in adults in 1997–1998 suggested that LAIV was more protective against the mismatched A/H3N2 strain. The relative efficacy of LAIV and TIV among young adults may vary depending on the specific population and the antigenic match between the vaccines and circulating strains. In adults 60 years of age and older, limited data suggest that the two vaccines are similarly effective. In children and adults, studies also suggest that the relative efficacy of LAIV versus TIV may increase when measured against more severe illness. Additional research comparing LAIV and TIV is needed in adults and would also be valuable in older children and adolescents. Studies should examine the role of pre‐existing immunity as well as vaccine impact on influenza illness of varying severity.

Modifications in the polymerase genes of a swine-like triple-reassortant influenza virus to generate live attenuated vaccines against 2009 pandemic H1N1 viruses

On 11 June 2009, the World Health Organization (WHO) declared that the outbreaks caused by novel swine-origin influenza A (H1N1) virus had reached pandemic proportions. The pandemic H1N1 (H1N1pdm) virus is the predominant influenza virus strain in the human population. It has also crossed the species barriers and infected turkeys and swine in several countries. Thus, the development of a vaccine that is effective in multiple animal species is urgently needed. We have previously demonstrated that the introduction of temperature-sensitive mutations into the PB2 and PB1 genes of an avian H9N2 virus, combined with the insertion of a hemagglutinin (HA) tag in PB1, resulted in an attenuated (att) vaccine backbone for both chickens and mice. Because the new pandemic strain is a triple-reassortant (TR) virus, we chose to introduce the double attenuating modifications into a swine-like TR virus isolate, A/turkey/OH/313053/04 (H3N2) (ty/04), with the goal of producing live attenuated influenza vaccines (LAIV). This genetically modified backbone had impaired polymerase activity and restricted virus growth at elevated temperatures. In vivo characterization of two H1N1 vaccine candidates generated using the ty/04 att backbone demonstrated that this vaccine is highly attenuated in mice, as indicated by the absence of signs of disease, limited replication, and minimum histopathological alterations in the respiratory tract. A single immunization with the ty/04 att-based vaccines conferred complete protection against a lethal H1N1pdm virus infection in mice. More importantly, vaccination of pigs with a ty/04 att-H1N1 vaccine candidate resulted in sterilizing immunity upon an aggressive intratracheal challenge with the 2009 H1N1 pandemic virus. Our studies highlight the safety of the ty/04 att vaccine platform and its potential as a master donor strain for the generation of live attenuated vaccines for humans and livestock.

Needle-free influenza vaccination

Vaccination is the cornerstone of influenza control in epidemic and pandemic situations. Influenza vaccines are typically given by intramuscular injection. However, needle-free vaccinations could offer several distinct advantages over intramuscular injections: they are pain-free, easier to distribute, and easier to give to patients, and their use could reduce vaccination costs. Moreover, vaccine delivery via the respiratory tract, alimentary tract, or skin might elicit mucosal immune responses at the site of virus entry and better cellular immunity, thus improving effectiveness. Although various needle-free vaccination methods for influenza have shown preclinical promise, few have progressed to clinical trials-only live attenuated intranasal vaccines have received approval, and only in some countries. Further clinical investigation is needed to help realise the potential of needle-free vaccination for influenza.

Effective induction of protective systemic immunity with nasally administered vaccines adjuvanted with IL-1

IL-1α and IL-1β were evaluated for their ability to provide adjuvant activity for the induction of serum antibody responses when nasally administered with protein antigens in mice and rabbits. In mice, intranasal (i.n.) immunization with pneumococcal surface protein A (PspA) or tetanus toxoid (TT) combined with IL-1β induced protective immunity that was equivalent to that induced by parenteral immunization. Nasal immunization of awake (i.e., not anesthetized) rabbits with IL-1-adjuvanted vaccines induced highly variable serum antibody responses and was not as effective as parenteral immunization for the induction of antigen-specific serum IgG. However, i.n. immunization of deeply anesthetized rabbits with rPA+IL-1α consistently induced rPA-specific serum IgG ELISA titers that were not significantly different than those induced by intramuscular (IM) immunization with rPA+alum although lethal toxin-neutralizing titers induced by nasal immunization were lower than those induced by IM immunization. Gamma scintigraphy demonstrated that the enhanced immunogenicity of nasal immunization in anesthetized rabbits correlated with an increased nasal retention of i.n. delivered non-permeable radio-labeled colloidal particles. Our results demonstrate that, in mice, IL-1 is an effective adjuvant for nasally administered vaccines for the induction of protective systemic immunity and that in non-rodent species, effective induction of systemic immunity with nasally administered vaccines may require formulations that ensure adequate retention of the vaccine within the nasal cavity.

The effects of preexisting immunity to influenza on responses to influenza vectors in mice

The use of viral vectors as vaccine candidates has shown promise against a number of pathogens. However, preexisting immunity to these vectors is a concern that must be addressed when deciding which viruses are suitable for use. A number of properties, including the existence of antigenically distinct subtypes, make influenza viruses attractive candidates for use as viral vectors. Here, we evaluate the ability of influenza viral vectors containing inserts of foreign pathogens to elicit antibody and CD8(+) T cell responses against these foreign antigens in the presence of preexisting immunity to influenza virus in mice. Specifically, responses to an H3N1-based vector expressing a 90 amino acid polypeptide derived from the protective antigen (PA) of Bacillus anthracis or an H1N1-based vector containing a CD8(+) T cell epitope from the glycoprotein (GP) of lymphocytic choriomeningitis virus were evaluated following infections with either homosubtypic or heterosubtypic influenza viruses. We found that mice previously infected with influenza viruses, even those expressing HA and NA proteins of completely different subtypes, were severely compromised in their ability to mount an immune response against the inserted epitopes. This inhibition was demonstrated to be mediated by CD8(+) T cells, which recognize multiple strains of influenza viruses. These CD8(+) T cells were further shown to protect mice from a lethal challenge by a heterologous influenza subtype. The implication of these data for the use of influenza virus vectors and influenza vaccination in general are discussed.

Reverse genetic platform for inactivated and live-attenuated influenza vaccine

Influenza vaccine strains have been traditionally developed by annual reassortment between vaccine donor strain and the epidemic virulent strains. The classical method requires screening and genotyping of the vaccine strain among various reassortant viruses, which are usually laborious and time-consuming. Here we developed an efficient reverse genetic system to generate the 6:2 reassortant vaccine virus from cDNAs derived from the influenza RNAs. Thus, cDNAs of the two RNAs coding for surface antigens, haemagglutinin and neuraminidase from the epidemic virus and the 6 internal genes from the donor strain were transfected into cells and the infectious viruses of 6:2 defined RNA ratio were rescued. X-31 virus (a high- growth virus in embryonated eggs) and its cold-adapted strain X-31 ca were judiciously chosen as donor strains for the generation of inactivated vaccine and live-attenuated vaccine, respectively. The growth properties of these recombinant viruses in embryonated chicken eggs and MDCK cell were indistinguishable as compared to those generated by classical reassortment process. Based on the reverse genetic system, we generated 6+2 reassortant avian influenza vaccine strains corresponding to the A/Chicken/Korea/ MS96 (H9N2) and A/Indonesia/5/2005 (H5N1). The results would serve as technical platform for the generation of both injectable inactivated vaccine and the nasal spray live attenuated vaccine for the prevention of influenza epidemics and pandemics.

Identification of seasonal vaccine hemagglutinin subtype 1 (H1) epitopes in Mexican isolates of the new influenza A (H1N1) 2009 virus

BACKGROUND

Pre-existing immunity in individuals is a determinant condition for epidemic dynamics. During the current influenza A (H1N1) virus pandemic, cross-reactivity of seasonal vaccines from the last years and previous contact with seasonal influenza viruses was suggested as the cause of low severity and low incidence of the disease in persons aged 50-65 years and with history of seasonal influenza vaccination.

METHODS

We performed a detailed search and analysis of 74 previously reported H1 epitopes present in influenza A virus contained in seasonal vaccines applied in Mexico from 2004 to date and in sequences from Mexican isolates from 2003, as well as in the recent influenza A (H1N1) 2009, and calculated the epitope conservation among vaccine, seasonal and pandemic influenza A (H1N1) virus.

RESULTS

H1 epitope sequence identity ranged from 61.53-100 %. Of the 74 epitopes previously reported, 31 (41.9%) were completely conserved among all sequences analyzed in this study, whereas 43 (58.1%) had changes in one or more amino acids.

CONCLUSIONS

Our findings contribute to the estimatation of the degree of epitope conservation among H1 from vaccine virus strains as well as in the different viruses that circulate in the Mexican population. These results may provide new elements to consider for analysis of cross-immunity to influenza viruses including the novel influenza A (H1N1) 2009 pandemic virus.

Induction of neutralizing antibody responses to anthrax protective antigen by using influenza virus vectors: implications for disparate immune system priming pathways

Viral vectors based on influenza virus, rabies virus (RV), and vaccinia virus (VV) were used to express large polypeptide segments derived from the Bacillus anthracis protective antigen (PA). For the infectious influenza virus vector and recombinant VV constructs, the receptor binding domain (RBD or domain 4) or the lethal and edema factor binding domain (LEF or domain 1') were engineered into functional chimeric hemagglutinin (HA) glycoproteins. In the case of the RV vector, the viral glycoprotein (G) was used as a carrier for RBD in an inactivated form of the vector. These constructs were examined by using multiple homologous and heterologous prime/boost immunization regimens in order to optimize the induction of alpha-PA antibody responses. Several immunization combinations were shown to induce high titers of antibody recognizing the anthrax RBD and LEF domains, as well as the full-length PA protein in mice. The heterologous prime/boost immunization regimens that involved an initial intranasal administration of a live influenza virus vector, followed by an intramuscular boost with either the killed RV vector or the VV vector, were particularly effective, inducing antigen-specific antibodies at levels severalfold higher than homologous or alternative heterologous protocols. Furthermore, sera from several groups of the immunized mice demonstrated neutralization activity in an in vitro anthrax toxin neutralization assay. In some cases, such toxin-neutralizing activity was notably high, indicating that the mechanisms by which immunity is primed by live influenza virus vectors may have beneficial properties.