Immunogenicity and safety of MF59-adjuvanted H5N1 influenza vaccine from infancy to adolescence

Astragalus polysaccharides combined with simvastatin as an immunostimulant enhances the immune adjuvanticity of oil-in-water emulsion and immune responses in mice

Oil-in-water emulsion-based adjuvants have demonstrated acceptable safety in many disease indications, while their adjuvant activities for vaccines still need to be improved. Recently, the strategy of combining adjuvants with multiple types of immunostimulants has been shown to enhance immune responses. In this study, astragalus polysaccharides were combined with simvastatin as an immunostimulant to construct a compound O/W emulsion adjuvant. The formulations were optimized according to the OVA-specific antibody responses induced in mice. For this reason, high (5 mg/mL), medium (2.5 mg/mL), and low (1.25 mg/mL) concentrations of astragalus polysaccharides and high (10 mg/mL), medium (1 mg/mL), and low (0.1 mg/mL) concentrations of simvastatin were selected. The final optimal formulation of the immunostimulant was a high concentration of astragalus polysaccharides combined with a medium concentration of simvastatin. The optimal compound O/W emulsion adjuvant could induce effective humoral and cellular immune responses that were stronger and more stable than those induced by aluminum adjuvant and Freund's adjuvant. The OVA/HAPS-MSim-OE induced dramatically strong and persistent IgG expressions and Th1-polarized immune responses. What's more, the highest CD4⁺/CD8⁺lymphocyte ratios were observed in OVA/HAPS-MSim-OE group. In addition, compound O/W emulsion adjuvant groups significantly promoted the secretion of IFN-γ and IL-6, which also indicated that the compound O/W emulsion adjuvants could induce both enhanced Th1 and Th2-mediated immune responses but prefer the Th1-mediated ones. This study would contribute to an interesting and promising direction in the development of emulsion-based adjuvants.

Safety, Tolerability and Immunogenicity of an MF59-adjuvanted, Cell Culture-derived, A/H5N1, Subunit Influenza Virus Vaccine: Results From a Dose-finding Clinical Trial in Healthy Pediatric Subjects

BACKGROUND

A/H5N1 influenza virus has significant pandemic potential, and vaccination is the main prophylactic measure. This phase 2, randomized, observer-blind, multicenter study evaluated the safety and immunogenicity of two MF59-adjuvanted, cell culture-derived H5N1 (aH5N1c) vaccine formulations in healthy pediatric subjects 6 months to 17 years old.

METHODS

Subjects (N = 662) received 2 aH5N1c doses 3 weeks apart, containing either 7.5 μg (full dose) or 3.75 μg (half dose) hemagglutinin antigen per dose. Local reactions and adverse events (AEs) were assessed by age. Antibody responses were measured by hemagglutination inhibition assay and assessed as geometric mean titers, geometric mean ratios (GMRs) and percentages of subjects achieving titers ≥1:40 and seroconversion (NCT01776554).

RESULTS

No vaccine-related serious AEs occurred. Incidence of solicited local reactions and systemic AEs were similar across vaccine groups. Tenderness and irritability in <6-year olds, and injection site pain, myalgia and fatigue in 6-17-year olds were the most commonly reported reactions in both full- and half-dose recipients. Frequencies of AEs were lower after the second dose than the first dose in all vaccine and age groups. Three weeks after the administration of a second dose, both full- and half-dose formulations met the Center for Biologics Evaluation Research and Review (United States) and Committee for Medicinal Products for Human Use (EU) licensure criteria for titers ≥1:40 (full dose 96% subjects; half dose 86%), seroconversion (full dose 96% subjects; half dose 86%), and GMR (full dose GMR 262; half dose 84). Antibody responses were highest in 6-35-month olds.

CONCLUSIONS

In pediatric subjects, both aH5N1c vaccine formulations were well tolerated and highly immunogenic, meeting both US and EU licensure criteria for pandemic influenza vaccines.

AS03- and MF59-Adjuvanted Influenza Vaccines in Children

Influenza is a major cause of respiratory disease leading to hospitalization in young children. However, seasonal trivalent influenza vaccines (TIVs) have been shown to be ineffective and poorly immunogenic in this population. The development of live-attenuated influenza vaccines and adjuvanted vaccines are important advances in the prevention of influenza in young children. The oil-in-water emulsions MF59 and adjuvant systems 03 (AS03) have been used as adjuvants in both seasonal adjuvanted trivalent influenza vaccines (ATIVs) and pandemic monovalent influenza vaccines. Compared with non-adjuvanted vaccine responses, these vaccines induce a more robust and persistent antibody response for both homologous and heterologous influenza strains in infants and young children. Evidence of a significant improvement in vaccine efficacy with these adjuvanted vaccines resulted in the use of the monovalent (A/H1N1) AS03-adjuvanted vaccine in children in the 2009 influenza pandemic and the licensure of the seasonal MF59 ATIV for children aged 6 months to 2 years in Canada. The mechanism of action of MF59 and AS03 remains unclear. Adjuvants such as MF59 induce proinflammatory cytokines and chemokines, including CXCL10, but independently of type-1 interferon. This proinflammatory response is associated with improved recruitment, activation and maturation of antigen presenting cells at the injection site. In young children MF59 ATIV produced more homogenous and robust transcriptional responses, more similar to adult-like patterns, than did TIV. Early gene signatures characteristic of the innate immune response, which correlated with antibody titers were also identified. Differences were detected when comparing child and adult responses including opposite trends in gene set enrichment at day 3 postvaccination and, unlike adult data, a lack of correlation between magnitude of plasmablast response at day 7 and antibody titers at day 28 in children. These insights show the utility of novel approaches in understanding new adjuvants and their importance for developing improved influenza vaccines for children.

Distinct patterns of cellular immune response elicited by influenza non-adjuvanted and AS03-adjuvanted monovalent H1N1(pdm09) vaccine

The study aimed at identifying biomarkers of immune response elicited by non-adjuvanted-(NAV) and adjuvanted-(AV) H1N1(pdm09) vaccines. The results showed that despite both vaccines elicited similar levels of anti-H1N1 antibodies at day30 after vaccination, higher reactivity was observed in AV at day180. While AV induced early changes in cell-surface molecules on monocytes, CD4⁺, CD8⁺ T-cells and B-cells, NAV triggered minor changes, starting later on at day3. Furthermore, AV induced a late and persistent increase in TLR gene expression after day3, except for tlr4, while NAV displayed earlier but transient tlr3/4/7/9 up-regulation. Contrasting with NAV, prominent chemokine gene expression (cxcl8,cxcl9,ccl5) and a broad spectrum up-regulation of plasmatic biomarkers (CXCL8,IL-6,IL-1β,IL-12,IL-10) was evident in AV, which showed a major involvement of TNF and IL-10. Similarly, AV induced a robust IL-10-modulated proinflammatory storm, with early and persistent involvement of TNF-α/IL-12/IFN-γ axis derived from NK-cells, CD4⁺ and CD8⁺ T-cells along with promiscuous production of IL-4/IL-5/IL-13. Conversely, NAV promotes a concise and restricted intracytoplasmic chemokine/cytokine response, essentially mediated by TNF-α and IL-4, with late IL-10 production by CD8⁺ T-cells. Systems biology approach underscored that AV guided the formation of an imbricate network characterized by a progressive increase in the number of neighborhood connections amongst innate and adaptive immunity. In AV, the early cross-talk between innate and adaptive immunity, followed by the triad NK/CD4⁺/CD8⁺ T-cells at day3, sponsored a later/robust biomarker network. These findings indicate the relevance of adjuvanted vaccination to orchestrate broad, balanced and multifactorial cellular immune events that lead ultimately to a stronger H1N1 humoral immunity.

An oil-in-water nanoemulsion enhances immunogenicity of H5N1 vaccine in mice

To enhance the immunogenicity of the Influenza H5N1 vaccine, we developed an oil-in-water nanoemulsion (NE) adjuvant. NE displayed good temperature stability and maintained particle size. More importantly, it significantly enhanced IL-6 and MCP-1 production to recruit innate cells, including neutrophils, monocytes/macrophages and dendritic cells to the local environment. Furthermore, NE enhanced dendritic cell function to induce robust antigen-specific T and B cell immune responses. NE-adjuvanted H5N1 vaccine not only elicited significantly higher and long-lasting antibody responses, but also conferred enhanced protection against homologous clade 1 as well as heterologous clade 2 H5N1 virus challenge in young as well as in aged mice. The pre-existing immunity to seasonal influenza did not affect the immunogenicity of NE-adjuvanted H5N1 vaccine.

The impact of size on particulate vaccine adjuvants

Particulate adjuvants have been successful at inducing increased immune responses against many poorly immunogenic antigens. However, the mechanism of action of these adjuvants often remains unclear. As more potential vaccine targets are emerging, it is becoming necessary to broaden our knowledge on the factors involved in generating potent immune responses to recombinant antigens with adjuvants. While composition of adjuvants is integral in defining the overall performance of an adjuvant, some physical parameters such as particle size, surface charge and surface modification may also contribute to the potency. In this review, we will try to highlight the role of particle size in controlling the immune responses to adjuvanted vaccines, with a focus on insoluble aluminum salts, oil-in-water emulsions, polymeric particles and liposomes.

A dose-ranging study of MF59(®)-adjuvanted and non-adjuvanted A/H1N1 pandemic influenza vaccine in young to middle-aged and older adult populations to assess safety, immunogenicity, and antibody persistence one year after vaccination

BACKGROUND

During development of an A/H1N1 pandemic influenza vaccine, this study was performed to identify the antigen and adjuvant content which would provide optimal antibody response and persistence in adults and the elderly. Dose-sparing strategies, such as inclusion of adjuvants, are critical in ensuring the widest possible population coverage in the event of an influenza pandemic, despite a limited global capacity for vaccine manufacture.

METHODS

Healthy subjects aged 18-64 years (n = 1240) and ≥65 years (n = 1352) were vaccinated with 1 of 8 investigational vaccine formulations varying in antigen quantity (3.75 µg to 30 µg of hemagglutinin) and MF59(®) adjuvant (none, half dose, or full dose). All subjects received 2 vaccine doses administered 3 weeks apart. Antibody response was assessed by hemagglutination inhibition assay 1 and 3 weeks after administration of first and second doses. Antibody persistence was assessed after 6 and 12 mo. Vaccine safety was monitored over 12 mo.

RESULTS

All 8 investigational A/H1N1 vaccine formulations were well tolerated, and rapidly induced high antibody titers which met all of the Center for Biologics Evaluation and Research (CBER) and Committee for Medicinal Products for Human Use (CHMP) licensure criteria 3 weeks after one dose. The highest antibody titers were observed in participants vaccinated with higher quantities of antigen and adjuvant.

CONCLUSION

A single vaccine dose containing 3.75 µg of A/California/7/2009 (H1N1) antigen with MF59 adjuvant was identified as optimal for young to middle-aged (18-64 years) and older (≥65 years) adult populations.

Systematic review of fever, febrile convulsions and serious adverse events following administration of inactivated trivalent influenza vaccines in children

In 2010, increased febrile convulsions (FC) occurred after administration of inactivated trivalent influenza vaccine (TIV) in Australia. We systematically reviewed the rates of fever, FC and serious adverse events (SAEs) after TIV, focussing on published and unpublished clinical trial data from 2005 to 2012, and performed meta-analysis of fever rates. From 4,372 records in electronic databases, 18 randomised controlled trials (RCTs), 14 non-randomised clinical trials, six observational studies and 12 registered trials (five RCTs and seven non-randomised) were identified. In published RCTs, fever ≥ 38 °C rates after first dose of non-adjuvanted TIV were 6.7% and 6.9% for children aged 6–35 months and ≥ 3 years, respectively. Analysis of RCTs by vaccine manufacturer showed pooled fever estimates up to 5.1% with Sanofi or GlaxoSmithKline vaccines; bioCSL vaccines were used in two non-randomised clinical trials and one unpublished RCT and were associated with fever in 22.5–37.1% for children aged 6–35 months. In RCTs, FCs occurred at a rate of 1.1 per 1,000 vaccinated children. While most TIVs induced acceptably low fever rates, bioCSL influenza vaccines were associated with much higher rates of fever in young children. Future standardised study methodology and access to individual level data would be illuminating.

Safety and immunogenicity of an MF59-adjuvanted A/H1N1 pandemic influenza vaccine in children from three to seventeen years of age

OBJECTIVES

This study was designed to identify the optimal dose of an MF59-adjuvanted, monovalent, A/H1N1 influenza vaccine in healthy paediatric subjects.

METHODS

Subjects aged 3-8 years (n=194) and 9-17 years (n=160) were randomized to receive two primary doses of A/H1N1 vaccine containing either 3.75 μg antigen with half a standard dose of MF59 adjuvant, 7.5 μg antigen with a full dose of MF59, or (children 3-8 years only), a non-adjuvanted 15 μg formulation. A booster dose of MF59-adjuvanted seasonal influenza vaccine including homologous A/H1N1 strain was given one year after priming. Immunogenicity was assessed by haemagglutination inhibition (HI) and microneutralization assays. Vaccine safety was assessed throughout the study (up to 18 months).

RESULTS

A single priming dose of either MF59-adjuvanted formulation was sufficient to meet the European licensure criteria for pandemic influenza vaccines (HI titres ≥1:40>70%; seroconversion>40%; and GMR>2.5). Two non-adjuvanted vaccine doses were required to meet the same licensure criteria. After first and second doses, percentage of subjects with HI titres ≥1:40 were between 97% and 100% in the adjuvanted vaccine groups compared with 68% and 91% in the non-adjuvanted group, respectively. Postvaccination seroconversion rates ranged from 91% to 98% in adjuvanted groups and were 68% (first dose) and 98% (second dose) in the non-adjuvanted group. HI titres ≥1:330 after primary doses were achieved in 69% to 90% in adjuvanted groups compared with 41% in the non-adjuvanted group. Long-term antibody persistence after priming and a robust antibody response to booster immunization were observed in all vaccination groups. All A/H1N1 vaccine formulations were generally well tolerated. No vaccine-related serious adverse events occurred, and no subjects were withdrawn from the study due to an adverse event.

CONCLUSIONS

An MF59-adjuvanted influenza vaccine containing 3.75 μg of A/H1N1 antigen was well tolerated and sufficiently immunogenic to meet all the European licensure criteria after a single dose in healthy children 3-17 years old.

Effect of influenza A(H5N1) vaccine prepandemic priming on CD4+ T-cell responses

Introduction. Previous priming with avian influenza vaccines results in more rapid and more robust neutralizing antibody responses upon revaccination, but the role CD4⁺ T cells play in this process is not currently known.

Methods. Human subjects previously enrolled in trials of inactivated influenza A(H5N1) vaccines and naive subjects were immunized with an inactivated subunit influenza A/Indonesia/5/05(H5N1) vaccine. Neutralizing antibody responses were measured by a microneutralization assay, and hemagglutinin (HA)-specific and nucleoprotein (NP)-specific CD4⁺ T-cell responses were quantified using interferon γ enzyme-linked immunosorbent spot assays.

Results. While vaccination induced barely detectable CD4⁺ T-cell responses specific for HA in the previously unprimed group, primed subjects had readily detectable HA-specific memory CD4⁺ T cells at baseline and mounted a more robust response to HA-specific epitopes after vaccination. There were no differences between groups when conserved NP-specific CD4⁺ T-cell responses were examined. Interestingly, neutralizing antibody responses following revaccination were significantly higher in individuals who mounted a CD4⁺ T-cell response to the H5 HA protein, a correlation not observed for NP-specific responses.

Conclusions. These findings suggest that prepandemic vaccination results in an enriched population of HA-specific CD4⁺ T cells that are recruited on rechallenge with a drifted vaccine variant and contribute to more robust and more rapid neutralizing antibody responses.

Phase I/II randomized double-blind study of the safety and immunogenicity of a nonadjuvanted vero cell culture-derived whole-virus H9N2 influenza vaccine in healthy adults

Studies on candidate pandemic vaccines against avian influenza viruses have focused on H5N1, but viruses of other subtypes, such as A/H9N2, are also considered to have pandemic potential. We investigated the safety and immunogenicity of two immunizations with one of five different antigen doses (ranging from 3.75 to 45 μg of hemagglutinin antigen) of a nonadjuvanted whole-virus G9 lineage H9N2 influenza virus vaccine in healthy adults aged 18 to 49 years. The antibody responses were measured by hemagglutination inhibition (HI), microneutralization (MN), and single radial hemolysis (SRH) assays. To investigate a hypothesis that previous exposure to H2N2 viruses in subjects born in or before 1968 might prime for more robust antibody responses to H9N2 vaccination than that in subjects born after 1968, a post hoc age-stratified analysis of antibody responses was done. Both vaccinations in all dose groups were safe and well tolerated. No vaccine-related serious adverse events were reported, and the majority of the adverse reactions were rated as mild. The rates of injection site reactions were lower in the 3.75-μg- and 7.5-μg-dose groups than those in the higher-dose groups; the rates of systemic reactions were similar across all dose groups. The seroprotection rates among the different dose groups 21 days after the second immunization ranged from 52.8% to 88.9% as measured by HI assay, from 88.7% to 98.1% or 82.7% to 96.2% as measured by MN assay (MN titer cutoffs, 1:40 and 1:80, respectively), and from 94.2% to 100% as measured by SRH assay. Higher antibody responses were not induced in subjects born in or before 1968. These data indicate that a nonadjuvanted whole-virus H9N2 vaccine is well tolerated and immunogenic in healthy adults. (This study has been registered at ClinicalTrials.gov under registration no. NCT01320696.).

Overview of Serological Techniques for Influenza Vaccine Evaluation: Past, Present and Future

Serological techniques commonly used to quantify influenza-specific antibodies include the Haemagglutination Inhibition (HI), Single Radial Haemolysis (SRH) and Virus Neutralization (VN) assays. HI and SRH are established and reproducible techniques, whereas VN is more demanding. Every new influenza vaccine needs to fulfil the strict criteria issued by the European Medicines Agency (EMA) in order to be licensed. These criteria currently apply exclusively to SRH and HI assays and refer to two different target groups-healthy adults and the elderly, but other vaccine recipient age groups have not been considered (i.e., children). The purpose of this timely review is to highlight the current scenario on correlates of protection concerning influenza vaccines and underline the need to revise the criteria and assays currently in use. In addition to SRH and HI assays, the technical advantages provided by other techniques such as the VN assay, pseudotype-based neutralization assay, neuraminidase and cell-mediated immunity assays need to be considered and regulated via EMA criteria, considering the many significant advantages that they could offer for the development of effective vaccines.

Safety and immunogenicity of a vero cell culture-derived whole-virus H5N1 influenza vaccine in chronically ill and immunocompromised patients

The development of vaccines against H5N1 influenza A viruses is a cornerstone of pandemic preparedness. Clinical trials of H5N1 vaccines have been undertaken in healthy subjects, but studies in risk groups have been lacking. In this study, the immunogenicity and safety of a nonadjuvanted cell culture-derived whole-virus H5N1 vaccine were assessed in chronically ill and immunocompromised adults. Subjects received two priming immunizations with a clade 1 A/Vietnam H5N1 influenza vaccine, and a subset also received a booster immunization with a clade 2.1 A/Indonesia H5N1 vaccine 12 to 24 months later. The antibody responses in the two populations were assessed by virus neutralization and single radial hemolysis assays. The T-cell responses in a subset of immunocompromised patients were assessed by enzyme-linked immunosorbent spot assay (ELISPOT). The priming and the booster vaccinations were safe and well tolerated in the two risk populations, and adverse reactions were predominantly mild and transient. The priming immunizations induced neutralizing antibody titers of ≥1:20 against the A/Vietnam strain in 64.2% of the chronically ill and 41.5% of the immunocompromised subjects. After the booster vaccination, neutralizing antibody titers of ≥1:20 against the A/Vietnam and A/Indonesia strains were achieved in 77.5% and 70.8%, respectively, of chronically ill subjects and in 71.6% and 67.5%, respectively, of immunocompromised subjects. The T-cell responses against the two H5N1 strains increased significantly over the baseline values. Substantial heterosubtypic T-cell responses were elicited against the 2009 pandemic H1N1 virus and seasonal A(H1N1), A(H3N2), and B subtypes. There was a significant correlation between T-cell responses and neutralizing antibody titers. These data indicate that nonadjuvanted whole-virus cell culture-derived H5N1 influenza vaccines are suitable for immunizing chronically ill and immunocompromised populations. (This study is registered at ClinicalTrials.gov under registration no. NCT00711295.).

GLA-AF, an emulsion-free vaccine adjuvant for pandemic influenza

The ongoing threat from Influenza necessitates the development of new vaccine and adjuvant technologies that can maximize vaccine immunogenicity, shorten production cycles, and increase global vaccine supply. Currently, the most successful adjuvants for Influenza vaccines are squalene-based oil-in-water emulsions. These adjuvants enhance seroprotective antibody titers to homologous and heterologous strains of virus, and augment a significant dose sparing activity that could improve vaccine manufacturing capacity. As an alternative to an emulsion, we tested a simple lipid-based aqueous formulation containing a synthetic TLR4 ligand (GLA-AF) for its ability to enhance protection against H5N1 infection. GLA-AF was very effective in adjuvanting recombinant H5 hemagglutinin antigen (rH5) in mice and was as potent as the stable emulsion, SE. Both adjuvants induced similar antibody titers using a sub-microgram dose of rH5, and both conferred complete protection against a highly pathogenic H5N1 challenge. However, GLA-AF was the superior adjuvant in ferrets. GLA-AF stimulated a broader antibody response than SE after both the prime and boost immunization with rH5, and ferrets were better protected against homologous and heterologous strains of H5N1 virus. Thus, GLA-AF is a potent emulsion-free adjuvant that warrants consideration for pandemic influenza vaccine development.

Pandemic influenza A H1N1 vaccines and narcolepsy: vaccine safety surveillance in action

The 2009 influenza A H1N1 pandemic placed unprecedented demand on public health authorities and the vaccine industry. Efforts were coordinated internationally to maximise the speed of vaccine development, distribution, and delivery, and the European Union's novel fast-track authorisation procedures mandated increased postmarketing surveillance to monitor vaccine safety. Clinicians in Finland and Sweden later identified an apparent increase in the incidence of narcolepsy associated with a specific adjuvanted pandemic influenza vaccine. After extensive review, the European Medicines Agency confirmed the existence of this association, which has since been detected in England, Ireland, France, and Norway. Assessments of the causal mechanisms continue. In this Review, we discuss how the narcolepsy association was detected, and we present the evidence according to the causality assessment criteria for adverse events following immunisation. The lessons learnt emphasise the central role of alert clinicians in reporting of suspected adverse reactions, and the importance of internationally robust postmarketing surveillance strategies as crucial components in future mass immunisation programmes.

H5N1 vaccines in humans

The spread of highly pathogenic avian H5N1 influenza viruses since 1997 and their virulence for poultry and humans has raised concerns about their potential to cause an influenza pandemic. Vaccines offer the most viable means to combat a pandemic threat. However, it will be a challenge to produce, distribute and implement a new vaccine if a pandemic spreads rapidly. Therefore, efforts are being undertaken to develop pandemic vaccines that use less antigen and induce cross-protective and long-lasting responses, that can be administered as soon as a pandemic is declared or possibly even before, in order to prime the population and allow for a rapid and protective antibody response. In the last few years, several vaccine manufacturers have developed candidate pandemic and pre-pandemic vaccines, based on reverse genetics and have improved the immunogenicity by formulating these vaccines with different adjuvants. Some of the important and consistent observations from clinical studies with H5N1 vaccines are as follows: two doses of inactivated vaccine are generally necessary to elicit the level of immunity required to meet licensure criteria, less antigen can be used if an oil-in-water adjuvant is included, in general antibody titers decline rapidly but can be boosted with additional doses of vaccine and if high titers of antibody are elicited, cross-reactivity against other clades is observed. Prime-boost strategies elicit a more robust immune response. In this review, we discuss data from clinical trials with a variety of H5N1 influenza vaccines. We also describe studies conducted in animal models to explore the possibility of reassortment between pandemic live attenuated vaccine candidates and seasonal influenza viruses, since this is an important consideration for the use of live vaccines in a pandemic setting.

Safety and immunogenicity of a vero cell culture-derived whole-virus influenza A(H5N1) vaccine in a pediatric population

BACKGROUND

Children are highly vulnerable to infection with novel influenza viruses. It is essential to develop candidate pandemic influenza vaccines that are safe and effective in the pediatric population.

METHODS

Infants and children aged 6-35 months and 3-8 years, respectively, were randomized to receive 2 immunizations with a 7.5-µg or 3.75-µg hemagglutinin (HA) dose of a nonadjuvanted whole-virus A/Vietnam(H5N1) vaccine; adolescents aged 9-17 years received a 7.5-µg dose only. A subset of participants received a booster immunization with an A/Indonesia(H5N1) vaccine approximately 1 year later. HA and neuraminidase antibody responses were assessed.

RESULTS

Vaccination was safe and well tolerated; adverse reactions were transient and predominantly mild. Two immunizations with the 7.5-µg dose of A/Vietnam vaccine induced virus microneutralization (MN) titers of ≥1:20 against the A/Vietnam strain in 68.8%-85.4% of participants in the different age groups. After the booster, 93.1%-100% of participants achieved MN titers of ≥1:20 against the A/Vietnam and A/Indonesia strains. Neuraminidase-inhibiting antibodies were induced in ≥90% of participants after 2 immunizations with the 7.5 µg A/Vietnam vaccine and in 100% of participants after the booster.

CONCLUSIONS

A whole-virus influenza A(H5N1) vaccine is suitable for prepandemic or pandemic immunization in a pediatric population.

CLINICAL TRIALS REGISTRATION

NCT01052402.

Vaccine adjuvant formulations: a pharmaceutical perspective

Formulation science is an unappreciated and often overlooked aspect in the field of vaccinology. In this review we highlight key attributes necessary to generate well characterized adjuvant formulations. The relationship between the adjuvant and the antigen impacts the immune responses generated by these complex biopharmaceutical formulations. We will use 5 well established vaccine adjuvant platforms; alum, emulsions, liposomes, PLG, and particulate systems such as ISCOMS in addition to immune stimulatory molecules such as MPL to illustrate that a vaccine formulation is more than a simple mixture of component A and component B. This review identifies the challenges and opportunities of these adjuvant platforms. As antigen and adjuvant formulations increase in complexity having a well characterized robust formulation will be critical to ensuring robust and reproducible results throughout preclinical and clinical studies.

Clinical vaccine development for H5N1 influenza

H5N1 is a highly pathogenic avian influenza virus that can cause severe disease and death in humans. H5N1 is spreading rapidly in bird populations and there is great concern that this virus will begin to transmit between people and cause a global crisis. Vaccines are the cornerstone strategy for combating avian influenza but there are complex challenges for pandemic preparedness including the unpredictability of the vaccine target and the manufacturing requirement for rapid deployment. The less-than-optimal response against the 2009 H1N1 pandemic unmasked the limitations associated with influenza vaccine production and in 2010, the President's Council of Advisors on Science and Technology re-emphasized the need for new recombinant-based vaccines and adjuvants that can shorten production cycles, maximize immunogenicity and satisfy global demand. In this article, the authors review the efforts spent in developing an effective vaccine for H5N1 influenza and summarize clinical studies that highlight the progress made to date.

Aflunov®: a vaccine tailored for pre-pandemic and pandemic approaches against influenza

INTRODUCTION

Aflunov is an egg-derived, subunit vaccine from Novartis Vaccines and Diagnostics containing 7.5 μg of hemagglutinin (HA) from the avian A/H5N1 virus and the oil-in-water adjuvant MF59.

AREAS COVERED

Aflunov behaves as a pre-pandemic vaccine. It has a good safety profile at all ages. At all ages, it induces high and persisting antibody titers and activation of HA-specific Th0/Th1 CD4(+) T cells, the levels of which correlate with the neutralizing antibody titers after a booster dose 6 months later. Aflunov triggers strong immunological memory, which persists for at least 6 - 8 years and can be rapidly boosted with a heterovariant vaccine strain, inducing very high neutralizing antibody titers within one week. These antibodies broadly and strongly cross-react with drifted H5N1 virus strains from various clades. Finally, the MF59 changes the pattern of HA recognition by antibodies that react with the HA1 more than with the HA2 region.

EXPERT OPINION

The available data show that Aflunov is a pre-pandemic vaccine suitable not only for stockpiling in case of a pandemic, but also before a pandemic is declared, with the ultimate objective of preventing the onset of an influenza pandemic.

Assessment of antigen-specific and cross-reactive antibody responses to an MF59-adjuvanted A/H5N1 prepandemic influenza vaccine in adult and elderly subjects

Preparedness against an A/H5N1 influenza pandemic requires well-tolerated, effective vaccines which provide both vaccine strain-specific and heterologous, cross-clade protection. This study was conducted to assess the immunogenicity and safety profile of an MF59-adjuvanted, prepandemic influenza vaccine containing A/turkey/Turkey/01/2005 (H5N1) strain viral antigen. A total of 343 participants, 194 adults (18 to 60 years) and 149 elderly individuals (≥61 years), received two doses of the investigational vaccine given 3 weeks apart. Homologous and heterologous antibody responses were analyzed by hemagglutination inhibition (HI), single radial hemolysis (SRH), and microneutralization (MN) assays 3 weeks after administration of the first vaccine dose and 3 weeks and 6 months after the second dose. Immunogenicity was assessed according to European licensure criteria for pandemic influenza vaccines. After two vaccine doses, all three European licensure criteria were met for adult and elderly subjects against the homologous vaccine strain, A/turkey/Turkey/1/2005, when analyzed by HI and SRH assays. Cross-reactive antibody responses were observed by HI and SRH analyses against the heterologous H5N1 strains, A/Indonesia/5/2005 and A/Vietnam/1194/2004, in adult and elderly subjects. Solicited local and systemic reactions were mostly mild to moderate in severity and occurred less frequently in the elderly than in adult vaccinees. In both adult and elderly subjects, MF59-adjuvanted vaccine containing 7.5 μg of A/Turkey strain influenza virus antigen was highly immunogenic, well tolerated, and able to elicit cross-clade, heterologous antibody responses against A/Indonesia and A/Vietnam strains 6 weeks after the first vaccination.

Assessment of squalene adjuvanted and non-adjuvanted vaccines against pandemic H1N1 influenza in children 6 months to 17 years of age

Vaccines were urgently needed in 2009 against A/H1N1 pandemic influenza. Based on the H5N1 experience, it was originally thought that 2 doses of an adjuvanted vaccine were needed for adequate immunogenicity. We tested H1N1 vaccines with or without AF03, a squalene-based adjuvant, in children.   Two randomized, open-label, trials were conducted. Participants 3-17 y received two injections of 3.8 µg or 7.5 µg hemagglutinin (HA) with adjuvant or 15 µg HA without adjuvant. Participants aged 6-35 mo received two injections of 1.9 µg or 3.8 µg HA with full or half dose adjuvant or 7.5 µg HA without adjuvant. All subjects 3 to 17 y reached seroprotection (hemagglutination inhibition (HI) titer ≥ 40) after the first dose of the adjuvanted vaccine, and 94% and 98% in the 3-8 and 9-17 y groups respectively with the non-adjuvanted vaccine. In children aged 6-35 mo responses were modest after one dose, but after two doses virtually all children were seroprotected regardless of HA or adjuvant dose. In this age group, antibody titers were 5 to 7 times higher after adjuvanted than non-adjuvanted vaccine. The higher responses with the adjuvanted vaccine were also reflected as better antibody persistence. There was no clustering of adverse events that would be suggestive of a safety signal. While a single injection was sufficient in subjects from 3 y, in children aged 6-35 mo two injections of this A/H1N1 pandemic influenza vaccine were required. Formulation of this vaccine with adjuvant provided a significant advantage for immunogenicity in the latter age group.

A non-adjuvanted whole-virus H1N1 pandemic vaccine is well tolerated and highly immunogenic in children and adolescents and induces substantial immunological memory

This phase 1/2 open-label, randomized clinical study investigated the safety and immunogenicity of a non-adjuvanted, whole virus, Vero cell-derived H1N1 pandemic influenza vaccine (A/H1N1/California/07/2009) in children and adolescents (6 months to 17 years). Subjects were stratified by age (6-11 months, 12-35 months, 3-8 years, 9-17 years) to receive two vaccinations 21 days apart of either the 3.75 μg or 7.5 μg dose. A booster with a licensed trivalent seasonal (2010/2011) influenza vaccine was administered one year after the first vaccination to a subgroup that had previously received the 7.5 μg dose. A single vaccination with the 7.5 μg dose induced high seroprotection rates in all subjects, namely: 88.0% (9-17 years); 68.0% (3-8 years); 42.9% (12-35 months); and 50.0% (6-11 months). Following a second vaccination, seroprotection rates ranged from 84.2% to 100%. GMTs after two vaccinations with the 7.5 μg dose (as determined by HI) were also substantial: reaching 210.0 (9-17 years), 196.2 (3-8 years), 118.9 (12-35 months) and 99.6 (6-11 months). Antibody persistence was demonstrated at 6 months (GMTs ranging from 65.6 to 212.8 with the 7.5 μg dose) and at 12 months (GMTs ranging from 33.6 to 124.1 with the 7.5 μg dose) after primary vaccination. The booster vaccination induced a strong response to the A/California/07/2009 strain, reaching 100% seroprotection in all age groups, with GMTs ranging from 640.0 to 886.3. The vaccine was well tolerated, inducing low adverse reaction rates (overall fever rate: 6% after the first vaccination; 7% after the second vaccination), even in young children. These data confirm that the H1N1 whole-virus Vero cell-derived pandemic influenza vaccine is suitable for use in children and adolescents; a 2-dose primary vaccination induces a memory response in a naïve population that can be effectively boosted with the A/H1N1/California/07/2009 component of a seasonal influenza vaccine. ClinicalTrials.gov Identifier: NCT00976469.

Aflunov(®): a prepandemic influenza vaccine

Influenza viruses are adept in human populations. Indeed, they have the capacity to evade the immune system through mechanisms of mutations (antigenic drift) and major variations in surface protein expression (antigenic shift). When a major change occurs, the risk of a human pandemic arises. Three influenza pandemics occurred during the 20th century, the most serious being the Spanish influenza. The last pandemic of the past century occurred in 1968, and the responsible virus infected an estimated 1-3 million people throughout the world. The first pandemic of the present century occurred in 2009 and was sustained by a H1N1 strain (A/California/07/09). In 1997, a novel avian influenza virus, H5N1, first infected humans in China. Since its emergence, the H5N1 virus has spread from Asia to Europe and Africa, resulting in the infection of millions of poultry and wild birds. So far, 522 human cases and 322 deaths have been reported by the WHO. Many studies have therefore been performed to obtain efficacious and safe H5N1 vaccines. One of these is Aflunov(®). Aflunov is a prepandemic monovalent A/H5N1 influenza vaccine adjuvanted with MF59 produced by Novartis Vaccines and Diagnostics. In nonclinical studies conducted in rabbits, Aflunov proved to be well-tolerated, did not cause maternal or embryo-fetal toxicity, was not teratogenic, and had no effects on postnatal development. In clinical studies, Aflunov proved safe and well-tolerated in infants, children, adolescents, adults and the elderly. In the same subjects, the vaccine elicited robust immunogenicity against both homologous (A/Vietnam/1194/2004 clade 1) and heterologous viral strains (for instance, A/Indonesia/05/2005 or A/Turkey/15/2006) and induced immunologic memory. Thus, in 2010, the CHMP issued a positive opinion on Aflunov and in January 2011 Aflunov was given marketing authorization. This vaccine could be very useful in the event of adaptation of the H5N1 virus to humans, which could cause a new pandemic.

Identification of antigen and adjuvant doses resulting in optimal immunogenicity and antibody persistence up to 1 year after immunization with a pandemic A/H1N1 influenza vaccine in children 3 to < 9 years of age

BACKGROUND

In the development of pediatric A/H1N1 influenza vaccines, this study was performed to identify antigen and adjuvant doses providing optimal immunogenicity and antibody persistence to ensure long-term immunity after immunization with an adjuvanted A/H1N1 vaccine in children 3 to <9 years of age.

METHODS

Healthy children (N = 1357) were immunized with 1 of 8 investigational vaccine formulations ranging in antigen (3.75-30 µg) and MF59 adjuvant (Novartis Vaccines, Marburg, Germany; 0, 50 and 100% of standard dose). Each participant received 2 vaccine doses given 3 weeks apart. Immunogenicity was analyzed by hemagglutination inhibition assay in sera drawn 3, 4 and 6 weeks after first vaccination. Long-term antibody persistence was assessed 6 and 12 months after immunization. Vaccine safety was monitored throughout the study.

RESULTS

All MF59-adjuvanted vaccines were well tolerated and highly immunogenic, with adjuvanted formulations inducing antibody titers statistically superior to those of the nonadjuvanted vaccines. Each MF59-adjuvanted vaccine met all the US and European licensure criteria for influenza vaccines 3 weeks after the administration of a single dose; all nonadjuvanted formulations failed to meet licensure criteria at this time point. Antibody titers in response to a single vaccination with 7.5 µg antigen and a full dose of MF59 continued to meet all US and European licensure criteria up to 1 year after immunization.

CONCLUSION

A single dose of vaccine containing 7.5 µg A/California/7/2009 (H1N1) antigen and a full dose of MF59 adjuvant was found to be optimal for children 3 to <9 years of age.

[Current events in vaccination]

The annual meeting of the Infectious Disease Society of America (IDSA) ; which brought together nearly 5000 participants from over 80 countries in Vancouver, Canada, October 21 to 24, 2010 ; provided a review of the influenza (H1N1) 2009 pandemic, evaluated vaccination programmes and presented new vaccines under development. With 12,500 deaths in the United States in 2009-2010, the influenza (H1N1) 2009 pandemic was actually less deadly than the seasonal flu. But it essentially hit the young, and the toll calculated in years of life lost is high. The monovalent vaccines, whether live attenuated or inactivated with or without adjuvants, were well tolerated in toddlers, children, adults and pregnant women. In order to protect infants against pertussis, family members are urged to get their booster shots. The introduction of the 13-valent Pneumococcal conjugated vaccine in the beginning of 2010 may solve - but for how long ? - the problem of serotype replacement, responsible for the re-increasing incidence of invasive Pneumococcal infections observed in countries that had introduced the 7-valent vaccine. The efficacy of a rotavirus vaccine has been confirmed, with a reduction in hospitalization in the United States and a reduction in gastroenteritis-related deaths in Mexico. In the United States, vaccination of pre-adolescents against human papillomavirus (HPV) has not resulted in any specific undesirable effects. Routine vaccination against chicken pox, recommended since 1995, has not had an impact on the evolution of the incidence of shingles. Vaccination against shingles, recommended in the United States for subjects 60 years and over, shows an effectiveness of 55 %, according to a cohort study (Kaiser Permanente, Southern California). Although some propose the development of personalized vaccines according to individual genetic characteristics, the priority remains with increasing vaccine coverage, not only in infants but also in adults and the elderly. Vaccine calendars that cover a whole lifetime should be promoted, since the vaccination of adults and seniors is a determining factor of good health at all ages.

Oil-in-water emulsion adjuvant with influenza vaccine in young children

BACKGROUND

The efficacy of inactivated influenza vaccines is known to be poor in infants and young children.

METHODS

We studied the effect of the adjuvant MF59, an oil-in-water emulsion, on the efficacy of trivalent inactivated influenza vaccine (TIV) in 4707 healthy children 6 to less than 72 months of age who had not previously been vaccinated against influenza. The children were randomly assigned to three study groups, each of which received the assigned vaccines in two doses, 28 days apart, during two consecutive influenza seasons. Two of the groups were given age-appropriate doses of TIV either with or without the MF59 adjuvant, and the third group was given control (noninfluenza) vaccines to assess their absolute and relative efficacy against influenza-like illness, as confirmed by means of polymerase-chain-reaction (PCR) assay.

RESULTS

Attack rates of influenza-like illness across both influenza seasons were 0.7%, 2.8%, and 4.7% in the adjuvant, nonadjuvant, and control vaccine groups, respectively. The absolute vaccine efficacy rates against all influenza strains (94 of 110 cases were due to vaccine-matched H3N2 viruses) were 86% (95% confidence interval [CI], 74 to 93) for the MF59-adjuvant vaccine (ATIV) and 43% (95% CI, 15 to 61) for the vaccine without the adjuvant (TIV); the relative vaccine efficacy rate for ATIV versus TIV was 75% (95% CI, 55 to 87). The efficacy rates for ATIV were 79% (95% CI, 55 to 90) in children 6 to less than 36 months of age and 92% (95% CI, 77 to 97) in those 36 to less than 72 months of age, as compared with 40% (95% CI, -6 to 66) and 45% (95% CI, 6 to 68), respectively, for TIV. Antibody responses were higher with ATIV and remained so through day 181. The rates of systemic and local reactions to the influenza vaccines with and without the adjuvant were similar in the younger age group (relative risk, 1.04; 95% CI, 0.98 to 1.09), but systemic events in the older age group were more frequent after administration of ATIV (63%) than after administration of TIV (44%) or the control vaccine (50%). Serious adverse events were distributed evenly across the three vaccine groups.

CONCLUSIONS

Influenza vaccine with the MF59 adjuvant is efficacious against PCR-confirmed influenza in infants and young children. (Funded by Novartis Vaccines and Diagnostics; ClinicalTrials.gov number, NCT00644059.).

Response to 2009 pandemic and seasonal influenza vaccines co-administered to HIV-infected and HIV-uninfected former drug users living in a rehabilitation community in Italy

BACKGROUND

2009 A(H1N1) pandemic influenza vaccination was recommended as a priority to essential workers and high-risk individuals, including HIV-infected patients and people living in communities.

METHODS

HIV-infected and HIV-uninfected former drug-users (18-60 years old) living in a rehabilitation community (San Patrignano, Italy) received one dose of a MF59-adjuvanted 2009 pandemic influenza vaccine and one dose of a 2009-2010 seasonal trivalent inactivated influenza vaccine (containing A/Brisbane/59/2007(H1N1), A/Brisbane/10/2007(H3N2), B/Brisbane/60/2008) simultaneously. Antibodies against each vaccine antigen were determined at the time of vaccination and one and six months post-vaccination by hemagglutination-inhibition test.

RESULTS

49 HIV-infected and 60 HIV-uninfected subjects completed the study. Most (98%) HIV-infected participants were on antiretroviral treatment, the median CD4+ cell count was 350 (IQR 300)cells/μl and viremia was suppressed in 91.8% of cases. One month post-vaccination, no significant changes in immune-virological parameters were observed. One month post-vaccination, the immune responses to both pandemic and seasonal vaccine met the EMA-CPMP criteria for immunogenicity of influenza vaccines in both HIV-infected and HIV-uninfected subjects. No difference in vaccine responses was observed between the two groups. Six months after vaccination, the percentages of vaccinees with antibody titres ≥1:40 and antibody geometric mean titres significantly decreased in both groups. However, they were significantly lower in HIV-infected than in HIV-uninfected vaccinees. In subjects who had been primed to seasonal influenza the year before (through either vaccination or natural infection), levels of antibodies against 2009 A(H1N1) were higher than those measured in unprimed subjects, both one month and six months post-vaccination.

CONCLUSIONS

The co-administration of a single dose of 2009 pandemic MF59-adjuvanted influenza vaccine with a seasonal vaccine provided a protective immune response in both HIV-infected and HIV-uninfected individuals. Subjects who had been primed to seasonal influenza in the year preceding the pandemic had a more vigorous and long-lasting antibody response to 2009 pandemic vaccine.

MF59 adjuvant: the best insurance against influenza strain diversity

MF59 is a well-established, safe and potent vaccine adjuvant that has been licensed for more than 13 years for use in an influenza vaccine focused on elderly subjects (Fluad®), Novartis, Cambridge, MA, USA). Recently, MF59 was shown to be safe in a seasonal influenza vaccine for young children and was able to increase vaccine efficacy from 43 to 89%. A key and consistent feature of MF59 is the ability of the emulsion to induce fast priming of influenza antigen-specific CD4(+) T-cell responses, to induce strong and long-lasting memory T- and B-cell responses and to broaden the immune response beyond the influenza strains actually included in the vaccine. The enhanced breadth of response is valuable in the seasonal setting, but is particularly valuable in a (pre-) pandemic setting, when it is difficult to predict which strain will emerge to cause the pandemic. We have shown that the ability of MF59 to increase the breadth of immune response against influenza vaccines is mainly due to the spreading of the repertoire of the B-cell epitopes recognized on the hemagglutinin and neuraminidase of the influenza virus.

Combined, concurrent, and sequential administration of seasonal influenza and MF59-adjuvanted A/H5N1 vaccines: a phase II randomized, controlled trial of immunogenicity and safety in healthy adults

OBJECTIVE

We performed a phase II randomized, controlled, open-label, single-center study (Centros de Estudios de Infectología Pediátrica, Colombia) to examine the feasibility of combined administration of seasonal and MF59-adjuvanted A/H5N1 influenza vaccines using extemporaneous mixing or simultaneous administration.

METHODS

The primary objective of the study was to assess the immunogenicity of seasonal influenza and A/H5N1 vaccines using European licensure criteria (Committee for Medicinal Products for Human Use [CHMP]); the secondary objective was to assess vaccine reactogenicity and safety.

RESULTS

In 401 healthy 18-40-year-old subjects, both vaccines were immunogenic in all settings; the vaccine for seasonal influenza met all CHMP criteria, unaffected by coadministration of A/H5N1 vaccine in separate or mixed injections. Likewise, the immunogenicity of A/H5N1 vaccine was unaffected by seasonal influenza vaccination, with hemagglutination inhibition seroprotection rates of 28%-40% after 1 dose and 67%-80% after 2 doses, sufficient to meet CHMP criteria. Solicited local and systemic adverse events were mainly mild to moderate. No vaccine-related serious adverse events were reported during the study period.

CONCLUSIONS

These data demonstrate that seasonal and MF59-adjuvanted A/H5N1 influenza vaccines can be given as a mixed injection or by simultaneous separate injections without affecting immunogenicity or safety, supporting the feasibility of incorporating prepandemic MF59-adjuvanted A/H5N1 vaccines into seasonal influenza vaccination programs and the development of tetravalent influenza vaccines, including pandemic strains. Clinical Trials Registration. NCT00481065.