Clinical experience with inactivated, virosomal influenza vaccine

Nanotechnology Platform for Advancing Vaccine Development against the COVID-19 Virus

The COVID-19 pandemic has had a profound impact on societies, public health, healthcare systems, and the world economy. With over 771 million people infected worldwide and a staggering death toll exceeding 6,960,783 as of 4 October 2023 (according to the World Health Organization), the urgency for a solution was paramount. Since the outbreak, the demand for immediate treatment for COVID-19 viral infection, as well as for effective vaccination against this virus, was soaring, which led scientists, pharmaceutical/biotech companies, government health agencies, etc., to think about a treatment strategy that could control and minimize this outbreak as soon as possible. Vaccination emerged as the most effective strategy to combat this infectious disease. For vaccination strategies, any conventional vaccine approach using attenuated live or inactivated/engineered virus, as well as other approaches, typically requires years of research and assessment. However, the urgency of the situation promoted a faster and more effective approach to vaccine development against COVID-19. The role of nanotechnology in designing, manufacturing, boosting, and delivering vaccines to the host to counter this virus was unquestionably valued and assessed. Several nanoformulations are discussed here in terms of their composition, physical properties, credibility, and applications in past vaccine development (as well as the possibility of using those used in previous applications for the generation of the COVID-19 vaccine). Controlling and eliminating the spread of the virus and preventing future recurrence requires a safe, tolerable, and effective vaccine strategy. In this review, we discuss the potential of nanoformulations as the basis for an effective vaccine strategy against COVID-19.

Developments in Vaccine Adjuvants

Vaccines, including subunit, recombinant, and conjugate vaccines, require the use of an immunostimulator/adjuvant for maximum efficacy. Adjuvants not only enhance the strength and longevity of immune responses but may also influence the type of response. In this chapter, we review the adjuvants that are available for use in human vaccines, such as alum, MF59, AS03, and AS01. We extensively discuss their composition, characteristics, mechanism of action, and effects on the immune system. Additionally, we summarize recent trends in adjuvant discovery, providing a brief overview of saponins, TLRs agonists, polysaccharides, nanoparticles, cytokines, and mucosal adjuvants.

A trivalent, inactivated influenza vaccine (Vaxigrip®): summary of almost 50 years of experience and more than 1.8 billion doses distributed in over 120 countries

INTRODUCTION

Vaxigrip, a trivalent split-virion, inactivated vaccine available since 1968 has been in use longer than any other influenza vaccine. It is the most widely-used influenza vaccine, with more than 1.8 billion doses distributed in more than 120 countries. Areas covered: The significant body of evidence that confirms the efficacy, effectiveness, immunogenicity, and safety of Vaxigrip in healthy individuals of all ages and at-risk populations is summarized. The results from at least 15 randomized efficacy trials and 15 other studies have demonstrated that vaccination with Vaxigrip is efficacious against various clinical endpoints. It was estimated that more than 37 million laboratory-confirmed influenza episodes, 476,000 influenza-related hospitalizations, and 67,000 influenza-related deaths have been avoided by the more than 1.8 billion doses of Vaxigrip that have been distributed, emphasizing its important public health impact. Expert commentary: This strong evidence base in favor of Vaxigrip provides a robust foundation to support the implementation of the quadrivalent formulation. This quadrivalent formulation of Vaxigrip contains two A and two B influenza strains (VaxigripTetra), and has a similar immunogenicity and safety profile to the trivalent formulation while offering broader protection due to the addition of the second influenza B strain.

Hemagglutination inhibiting antibody persistence 1 year after influenza vaccination in Korean children and adolescents

This study aimed to assess the 1-y immunogenicity of influenza vaccines and the association between immunogenicity at 1 m and further influenza infections in children aged 6 m to 18 y. Serum hemagglutination inhibition (HI) antibody titers and GMTs were determined for the recommended influenza strains 0, 1, 6, and 12 m post-vaccination. The serological evidence of influenza infections were defined as the increase of HI titer (HI ≥1:40 and 4-fold rise). The seroprotection rates for strains A(H1N1), A(H3N2), and B were 91.2%, 87.6%, and 87.6%, respectively, at 1 month (n = 174). These rates were 76.5%, 64.7%, and 54.6%, respectively, at 12 m. The seroprotection rates and GMTs for influenza A(H1N1) and A(H3N2) were higher at 12 m than at 0 m (p < 0.05) but not for B. There were 39 subjects (42 cases) of serological influenza infections. Subjects with seroprotection at 1 m post-vaccination had showed fewer serologic A(H1N1) (10.1 vs 54.5%) and A(H3N2) (7.2 vs 38.1%) infections than the ones with HI titer <1:40 during follow-up (P < 0.01). In conclusion, influenza vaccines used during the 2008-09 season induced adequate 1-y immunogenicity for A(H1N1) and A(H3N2). The immunogenicity at one month after vaccination influenced further serological influenza infections.

Liposomal adjuvants for human vaccines

INTRODUCTION

Liposomes are well-known as drug carriers, and are now critical components of two of six types of adjuvants present in licensed vaccines. The liposomal vaccine adjuvant field has long been dynamic and innovative, and research in this area is further examined as new commercial products appear in parallel with new vaccines. In an arena where successful products exist the potential for new types of vaccines with liposomal adjuvants, and alternative liposomal adjuvants that could emerge for new types of vaccines, are discussed.

AREAS COVERED

Major areas include: virosomes, constructed from phospholipids and proteins from influenza virus particles; liposomes containing natural and synthetic neutral or anionic phospholipids, cholesterol, natural or synthetic monophosphoryl lipid A, and QS21 saponin; non-phospholipid cationic liposomes; and combinations and mixtures of liposomes and immunostimulating ingredients as adjuvants for experimental vaccines.

EXPERT OPINION

Liposomes containing monophosphoryl lipid A and QS21 have considerable momentum that will result soon in emergence of prophylactic vaccines to malaria and shingles, and possible novel cancer vaccines. The licensed virosome vaccines to influenza and hepatitis A will be replaced with virosome vaccines to other infectious diseases. Alternative liposomal formulations are likely to emerge for difficult diseases such as tuberculosis or HIV-1 infection.

Vaccine-preventable diseases: from paediatric to adult targets

The morbidity and mortality related to many communicable infectious diseases have significantly decreased in Western countries largely because of the use of antibiotics, and the implementation of well-planned vaccination strategies and national immunisation schedules specifically aimed at infants and children. However, although immunisation has proved to be highly effective for public health, more effort is needed to improve the currently sub-optimal rates of vaccination against various diseases among adults who may be at risk because of their age, medical condition or occupation. The vaccines currently licenced in Western countries are safe, immunogenic and effective against many infectious diseases and their complications, but the availability of newer vaccines or vaccines with new indications, the evolving ecology and epidemiology of many infections, population ageing, and other demographic changes (i.e. the increasing prevalence of chronic comorbidities and immunodeficiencies, mass migration, new working relationships, and widespread international tourism) require changes in the approach to immunisation. There is now a need for appropriate preventive measures for adults and the elderly aimed at protecting people at risk by using every possible catch-up opportunity and recommending specific age-related schedules on the basis of local epidemiology.

Influenza virosomes supplemented with GPI-0100 adjuvant: a potent vaccine formulation for antigen dose sparing

Adjuvants can stimulate vaccine-induced immune responses and can contribute decisively to antigen dose sparing when vaccine antigen production is limited, as for example during a pandemic influenza outbreak. We earlier showed that GPI-0100, a semi-synthetic saponin derivative with amphiphilic structure, significantly stimulates the immunogenicity and protective efficacy of influenza subunit vaccine administered via a systemic route. Here, we evaluated the adjuvant effect of GPI-0100 on a virosomal influenza vaccine formulation. In contrast to influenza subunit vaccine adjuvanted with GPI-0100, virosomal vaccine supplemented with the same dose of GPI-0100 provided full protection of mice against infection at the extremely low antigen dose of 2 × 8 ng hemagglutinin. Overall, adjuvanted virosomes elicited higher antibody and T-cell responses than did adjuvanted subunit vaccine. The enhanced immunogenicity of the GPI-0100-adjuvanted virosomes, particularly at low antigen doses, is possibly due to a physical association of the amphiphilic adjuvant with the virosomal membrane. These results show that a combination of GPI-0100 and a virosomal influenza vaccine formulation is highly immunogenic and allows the use of very low antigen doses without compromising the protective potential of the vaccine.

Immunogenicity and safety of seasonal influenza vaccination in patients with classic Kaposi's sarcoma

Classic Kaposi's sarcoma (cKS) is a human herpesvirus-8 (HHV-8)-associated lympho-angioproliferative tumor typically occurring in the elderly. It is associated with HHV-8-driven perturbed balance of peripheral B-cell subsets, which may have an impact on immune responses to antigenic stimulation. We took advantage of the common practice of cKS patients to undergo seasonal influenza vaccination because of advanced age and analyzed the immunogenicity and safety of licensed trivalent influenza vaccine in 46 cKS patients and 44 matched controls. Licensure criteria for immunogenicity were fulfilled in both groups. Four weeks after vaccination, hemagglutination-inhibition antibody titers against each viral strain contained in the vaccine increased in patients and controls (all P<0.001). Protection against at least one strain was achieved by 96% of cKS and 91% of control subjects. Protection against all strains persisted after 12 weeks, demonstrating a long-lasting response to vaccination. The vaccine was equally well tolerated by patients and controls, as assessed by evaluating solicited local and systemic reactions to the vaccine, and appearance or increase of antinuclear autoantibodies. HHV-8 virological rebound was observed in four cKS patients, but was not accompanied by progression of KS lesions. We conclude that seasonal influenza vaccine given to cKS patients is immunogenic and safe.

Immunogenicity and safety of inactivated influenza vaccines in primed populations: a systematic literature review and meta-analysis

Several inactivated influenza vaccine formulations for systemic administration in man are currently available for annual (seasonal) immunization: split virus and subunit (either plain-aqueous, or virosomal, or adjuvanted by MF59). From a literature search covering the period 1978-2009, 33 articles could be identified, which described randomized clinical trials comparing at least two of the four vaccine formulations with respect to serum hemagglutination inhibition (HI) antibody response, local and systemic vaccine reactions and serious adverse events after vaccination, and employing seasonal vaccine components and doses. In total, 9121 vaccinees of all ages, either healthy or with underlying diseases, were involved. Most vaccinees were primed or had been vaccinated in previous years. For immunogenicity, homologous post-vaccination geometric mean HI titers (GMTs) were analyzed by a random effects model for continuous data. Unreported standard deviations (SD) were addressed by imputing assumed SD-values. Age and health state of the vaccinees appeared to have little influence on the outcome. The immunogenicity of split, aqueous and virosomal subunit formulations were similar, with geometric mean ratio values (GMR, quotient of paired GMT-values) varying around one (0.93-1.24). The MF59-adjuvanted subunit vaccine induced, on average, larger antibody titers than the non-adjuvanted vaccine formulations, but the absolute increase was small (GMR-values varying between 1.25 and 1.40). Vaccine reactions were analyzed using a random effects model for binary data. Local and systemic reactogenicity was similar among non-adjuvanted formulations. The adjuvanted subunit formulation was more frequently associated with local reactions than the non-adjuvanted formulations (rate ratio: 2.12, significant). Systemic reactions were similar among all vaccine formulations. The original articles emphasized the mild and transient character of the vaccine reactions and the absence of serious vaccine-related adverse events. This adequate amount of evidence led to the conclusion that all the currently available inactivated influenza vaccine formulations are safe, well tolerated and similarly effective to control seasonal influenza outbreaks across primed populations and age ranges.

Inactivated influenza vaccines: recent progress and implications for the elderly

The current public health strategy for the containment of influenza is annual vaccination, which is recommended for the elderly and for those in risk factor categories that present the highest morbidity and mortality. However, because the immune response in the elderly is known to be less vigorous than in younger adults, research in the last decade has focused on improving the immune response to vaccination and increasing the protection of aged populations. The decreased efficacy of vaccines in the elderly is due to several factors, such as a decrease in the number of Langerhans cells, the limited capacity of dendritic cells to present antigen, defects in the expression of Toll-like receptors and the reduced expression of MHC class I and II molecules. Also, production of mature naive T cells by the thymus decreases with age. Among several approaches proposed to address the need for more immunogenic vaccines compared with conventional agents, the most well proven is the use of adjuvants. The first licensed adjuvant, aluminium-based mineral salts (alum), introduced in the 1920s, remains the standard worldwide adjuvant for human use and it has been widely used for almost a century. However, the addition of alum adjuvant to a split or subunit influenza vaccine has induced only marginal improvements. Other adjuvants have been developed and approved for human use since 1997; in particular, MF59, an oil-in-water adjuvant emulsion of squalene, which is able to increase immunogenicity of seasonal, pre-pandemic and pandemic subunit vaccines while maintaining acceptable safety and tolerability profiles. More recently, another oil-in-water emulsion, AS03, has been approved as a component of pre-pandemic H5N1 and pandemic H1N1 2009 vaccines. Besides adjuvants, several other strategies have been assessed to enhance antibody response in the elderly and other less responsive subjects, such as high-dose antigen vaccines, carrier systems (liposomes/virosomes) and the intradermal route of immunization. In particular, the potential of intradermal vaccination is well documented and the recent availability of an appropriate injection system, which combines simplicity, safety and ease of use, has allowed evaluation of the tolerability, safety and immunogenicity of the intradermal influenza vaccine in large numbers of subjects. Data that emerged from large clinical trials showed an improved immunogenicity compared with that of standard vaccine. Observational studies or comparisons between adjuvanted, intradermal or high-dose versus conventional vaccines are needed to evaluate whether the greater immunogenicity observed in a number of recent studies is correlated with greater protection against influenza and influenza-related complications and death.

Influenza vaccines provide diminished protection but are cost-saving in older adults

Influenza is associated with substantial morbidity and mortality in adults aged over 65 years. Although vaccination remains the most effective method of preventing influenza and its sequellae, current vaccination strategies provide less protection to older adults than to younger persons. Influenza vaccination in community-dwelling older adults is cost-effective, though there is room for improvement. Newer vaccine strategies considered for use in older adults include alternate routes of administration (intradermal or intranasal), addition of adjuvant, and novel methods of antigen presentation. Measuring cell-mediated immune response to new vaccines in addition to antibody response may correlate better with vaccine efficacy in this population. Whilst pandemic influenza A/H1N1 2009 (pH1N1) has largely spared older adults, the impact of pH1N1 vaccination has yet to be determined.

MF59®-adjuvanted seasonalinfluenza vaccine

Correlated with increasing chronologic age, immunosenescence impairs the response to influenza vaccines. MF59®-adjuvanted influenza vaccine (Fluad®, Novartis, Basel, Switzerland) elicits a stronger and broader immune response against well-matched and drifted influenza strains compared with conventional vaccines. MF5-adjuvanted influenza vaccine reduces the rate of hospitalization for pneumonia, cardiovascular disease and cerebrovascular disease, even in seasons with an imperfect match between the vaccine and circulating strains, in vaccinated compared with unvaccinated older adults.

Vaccines for an influenza pandemic: scientific and political challenges

So far, most published results from clinical trials using various avian influenza virus vaccine formulations have been disappointing. Should the pandemic strike, we still do not have the ability to provide an efficacious pandemic vaccine in time and in sufficient quantities for the world. The H5N1 enzootic could potentially give rise to a pandemic at any time. Transcontinental air traffic could seed the pandemic virus to most corners of the globe within a few weeks/months. We still have a unique window of opportunity to stimulate and support academia and the pharmaceutical industry to accelerate the urgently needed vaccine research. The political inertia is surprising, particularly as politicians, if and when a pandemic eventuates, will be asked why, despite repeated warnings, they did not take appropriate action in time. It is a governmental obligation--and not that of the WHO or the pharmaceutical industry--to protect their nationals. Moreover, when the poorer nations of this world realize that equitable quantities of the scarce supplies of vaccines, drugs and medical essentials will not come their way, the post-pandemic international scene will be one of even more deep distrust for many years. This scenario is not acceptable.

Long-lasting immunogenicity of a virosomal vaccine in older children and young adults with type I diabetes mellitus

To evaluate the long-lasting immunogenicity and reactogenicity of a virosomal influenza vaccine in subjects with type I diabetes, a trial was conducted during the 2007-2008 influenza season in Milan, Northern Italy. One hundred five subjects aged 9-30 years were randomized to receive by intramuscular injection vaccination by a single dose (0.5 ml) of either a virosomal (Inflexal V) (n=52) or a standard subunit (Influvac) (n=53) vaccine. Serum hemagglutinin inhibition antibody titres were determined against the three recommended influenza-like strains, A/H1N1, A/H3N2 and B, at pre-vaccination, and 1 and 6 months post-vaccination. Geometric mean titres were increased in the two groups 1 and 6 months post-vaccination (P<0.001). One month post-vaccination both vaccines met the CPMP requirement for immunogenicity with high seroprotection rates (>95%) for strains A/H1N1 and A/H3N2, and a seroprotection of 73% and 70% in the virosomal and subunit vaccine for strain B. Mean fold increase ranged 2.8 (A/H3N2)-6.2 (A/H1N1) in the virosomal group and 2.3 (A/H3N2)-4.8 (A/H1N1) in the subunit group. Immunogenicity declined 6 months post-vaccination in both groups, and the CPMP requirement for immunogenicity was satisfied only in the virosomal group. In subjects without pre-existing antibodies to strain B (titre <10), the virosomal vaccine showed higher immune response than the subunit vaccine 6 months post-vaccination, with a geometric mean titre (95% CI) of 40.2 (30.7-54.6) vs. 21.2 (14.6-30.8). Reactogenicity was similar in the two vaccines. All reactions were transient and not severe. The results indicate that in older children and young adults with type I diabetes influenza vaccination with a virosomal or a standard subunit vaccine is safe and adequately immunogenic against the three influenza vaccine strains. In addition, the virosomal vaccine may show better long-lasting immune response than the standard subunit vaccine, especially in subjects without pre-existing antibodies to influenza strains.

Influenza control in the 21st century: Optimizing protection of older adults

Older adults (> or =65 years of age) are particularly vulnerable to influenza illness. This is due to a waning immune system that reduces their ability to respond to infection, which leads to more severe cases of disease. The majority ( approximately 90%) of influenza-related deaths occur in older adults and, in addition, catastrophic disability resulting from influenza-related hospitalization represents a significant burden in this vulnerable population. Current influenza vaccines provide benefits for older adults against influenza; however, vaccine effectiveness is lower than in younger adults. In addition, antigenic drift is also a concern, as it can impact on vaccine effectiveness due to a mismatch between the vaccine virus strain and the circulating virus strain. As such, vaccines that offer higher and broader protection against both homologous and heterologous virus strains are desirable. Approaches currently available in some countries to meet this medical need in older adults may include the use of adjuvanted vaccines. Future strategies under evaluation include the use of high-dose vaccines; novel or enhanced adjuvantation of current vaccines; use of live attenuated vaccines in combination with current vaccines; DNA vaccines; recombinant vaccines; as well as the use of different modes of delivery and alternative antigens. However, to truly evaluate the benefits that these solutions offer, further efficacy and effectiveness studies, and better correlates of protection, including a precise measurement of the T cell responses that are markers for protection, are needed. While it is clear that vaccines with greater immunogenicity are required for older adults, and that adjuvanted vaccines may offer a short-term solution, further research is required to exploit the many other new technologies.

Improving seasonal and pandemic influenza vaccines

Abstract  Challenges facing seasonal and pandemic influenza vaccination include: increasing the immunogenicity of seasonal vaccines for the most vulnerable, increasing vaccination coverage against seasonal influenza, and developing vaccines against pandemic strains that are immunogenic with very low quantities of antigen to maximize the number of people who can be vaccinated with a finite production capacity. We review Sanofi Pasteur’s epidemic and pandemic influenza research and development programmes with emphasis on two key projects: intradermal influenza vaccine for seasonal vaccination of both elderly and younger adults, and pandemic influenza vaccine.

Eleven years of Inflexal V-a virosomal adjuvanted influenza vaccine

Since the introduction to the Swiss market in 1997, Crucell (former Berna Biotech Ltd.), has sold over 41 million doses worldwide of the virosomal adjuvanted influenza vaccine, Inflexal V. Since 1992, 29 company sponsored clinical studies investigating the efficacy and safety of Inflexal V have been completed in which 3920 subjects participated. During its decade on the market, Inflexal V has shown an excellent tolerability profile due to its biocompatibility and purity. The vaccine contains no thiomersal or formaldehyde and its purity is reflected in the low ovalbumin content. By mimicking natural infection, the vaccine is highly efficacious. Inflexal V is the only adjuvanted influenza vaccine licensed for all age groups and shows a good immunogenicity in both healthy and immunocompromised elderly, adults and children. This review presents and discusses the experience with Inflexal V during the past decade.

Head-to-head comparison of four nonadjuvanted inactivated cell culture-derived influenza vaccines: effect of composition, spatial organization and immunization route on the immunogenicity in a murine challenge model

In order to study the influence of antigen composition, spatial organization of antigen and the route of administration, four cell culture-derived, inactivated, nonadjuvanted influenza vaccine formulations, i.e. whole inactivated virus (WIV), split, subunit and virosome vaccines were prepared from a single antigen batch. We directly compared the immunogenicity and efficacy of these vaccine formulations after intramuscular (i.m.) or intranasal (i.n.) administration in mice. Prime and boost vaccination were followed by a potentially lethal homologous aerosol challenge. For all vaccines, the i.m. route induced higher serum humoral immune responses as compared to the i.n. route and protected all mice against challenge at a dose of 5 microg. Upon i.n. immunization only WIV and split vaccines induced detectable IgG titers and partial protection against challenge but only very low HI titers were induced in almost all mice. WIV induced mainly IgG2a/c titers via both routes, whereas split vaccine induced exclusively IgG1 titers via both routes. Subunit and virosome vaccines induced exclusively IgG1 via the i.m. route. Mucosal sIgA levels were only detected after i.n. vaccination with WIV. Furthermore, vaccines containing all viral components (WIV and split vaccine) induced higher serum HI titers and serum antibody titers than subunit and virosome vaccines. The differences in magnitude and quality of immune responses of split and WIV, having the same composition, are likely related to their distinct spatial organization. In conclusion, the direct comparison between WIV, split, subunit and virosomes, shows that the differences in immune responses between these well known influenza vaccines can be explained by both the composition and particulate structure of these vaccine formulations.

Development of stable influenza vaccine powder formulations: challenges and possibilities

Influenza vaccination represents the cornerstone of influenza prevention. However, today all influenza vaccines are formulated as liquids that are unstable at ambient temperatures and have to be stored and distributed under refrigeration. In order to stabilize influenza vaccines, they can be brought into the dry state using suitable excipients, stabilizers and drying processes. The resulting stable influenza vaccine powder is independent of cold-chain facilities. This can be attractive for the integration of the vaccine logistics with general drug distribution in Western as well as developing countries. In addition, a stockpile of stable vaccine formulations of potential vaccines against pandemic viruses can provide an immediate availability and simple distribution of vaccine in a pandemic outbreak. Finally, in the development of new needle-free dosage forms, dry and stable influenza vaccine powder formulations can facilitate new or improved targeting strategies for the vaccine compound. This review represents the current status of dry stable inactivated influenza vaccine development. Attention is given to the different influenza vaccine types (i.e. whole inactivated virus, split, subunit or virosomal vaccine), the rationale and need for stabilized influenza vaccines, drying methods by which influenza vaccines can be stabilized (i.e. lyophilization, spray drying, spray-freeze drying, vacuum drying or supercritical fluid drying), the current status of dry influenza vaccine development and the challenges for ultimate market introduction of a stable and effective dry-powder influenza vaccine.

Nanotechnology in vaccine delivery

With very few adjuvants currently being used in marketed human vaccines, a critical need exists for novel immunopotentiators and delivery vehicles capable of eliciting humoral, cellular and mucosal immunity. Such crucial vaccine components could facilitate the development of novel vaccines for viral and parasitic infections, such as hepatitis, HIV, malaria, cancer, etc. In this review, we discuss clinical trial results for various vaccine adjuvants and delivery vehicles being developed that are approximately nanoscale (< 1000 nm) in size. Humoral immune responses have been observed for most adjuvants and delivery platforms while only viral vectors, ISCOMs and Montanide™ ISA 51 and 720 have shown cytotoxic T cell responses in the clinic. MF59 and MPL® have elicited Th1 responses, and virus-like particles, non-degradable nanoparticles and liposomes have also generated cellular immunity. Such vaccine components have also been evaluated for alternative routes of administration with clinical successes reported for intranasal delivery of viral vectors and proteosomes and oral delivery of a VLP vaccine.

Inulin sugar glasses preserve the structural integrity and biological activity of influenza virosomes during freeze-drying and storage

Influenza virosomes are reconstituted influenza virus envelopes that may be used as vaccines or as carrier systems for cellular delivery of therapeutic molecules. Here we present a procedure to generate influenza virosomes as a stable dry-powder formulation by freeze-drying (lyophilization) using an amorphous inulin matrix as a stabilizer. In the presence of inulin the structural integrity and fusogenic activity of virosomes were fully preserved during freeze-drying. For example, the immunological properties of the virosomes, i.e. the HA potency in vitro and the immunogenic potential in vivo, were maintained during lyophilization in the presence of inulin. In addition, compared to virosomes dispersed in buffer, inulin-formulated virosomes showed substantially prolonged preservation of the HA potency upon storage. Also the capacity of virosomes to mediate cellular delivery of macromolecules was maintained during lyophilization in the presence of inulin and upon subsequent storage. Specifically, when dispersed in buffer, virosomes with encapsulated plasmid DNA lost their transfection activity completely within 6 weeks, whereas their transfection activity was fully preserved for at least 12 weeks after incorporation in an inulin matrix. Thus, in the presence of inulin as a stabilizing agent, the shelf-life of influenza virosomes with and without encapsulated macromolecules was considerably prolonged. Formulation of influenza virosomes as a dry-powder is advantageous for storage and transport and offers the possibility to develop needle-free dosage forms, e.g. for oral, nasal, pulmonal, or dermal delivery.

Long-term immunogenicity of a virosomal subunit inactivated influenza vaccine in children with asthma

To evaluate long-term immunogenicity of a virosomal subunit inactivated influenza vaccine in children with asthma, a prospective study was conducted during 2005-2006 influenza season in six public pediatric clinics in Milan and surroundings, Northern Italy. A single dose (0.5 ml) of a virosomal subunit inactivated influenza vaccine (Inflexal V) was injected in 106 asthmatic children aged 3-9 years. Serum hemagglutinin inhibition antibody titers were determined against the recommended influenza strains A/New Caledonia (H1N1), A/California (H3N2), and B/Shanghai (B), at pre-vaccination and 1 and 6 months after vaccination. Seroconversion rate (95% CI) against the strains A/H1N1, A/H3N2 and B was, respectively, 78% (68.6-85.7), 57% (46.7-66.9) and 66% (55.8-71.2) at 1 month. Seroprotection (titer> or =40) rate for A/H1N1, A/H3N2 and B was, respectively, 87% (77.8-92.2), 82% (72.6-89.7) and 90% (82.6-94.8) at 1 month and 74% (64.3-82.3), 77% (67.5-84.8), and 77% (67.5-84.8) at 6 months. Seroprotection rate was high and persistent (>95%) in children with pre-existing antibodies (titer> or =10) at pre-vaccination for any specific strain. In children without pre-existing antibodies, seroprotection rate for A/H1N1, A/H3N2 and B was, respectively, 67.6%, 66.7% and 74.4% at 1 month, and 35.1%, 56.2% and 41.0% at 6 months after vaccination. Vaccine was well tolerated. These results indicate that in unvaccinated children with asthma vaccination with a single dose of virosomal-adjuvanted influenza vaccine is well tolerated and effective as a whole. However, while immunity response and persistence are excellently high in children with pre-existing antibodies, in children naive for the antigens the immune parameters are lower at 6 months after vaccination.

Clinical evaluation of vaccines for pandemic influenza H5N1

Avian influenza (H5N1) was first associated with human respiratory disease in Hong Kong in 1997. In 2004 the virus re-emerged among poultry and migratory birds in Asia and has spread into Europe and Africa, raising concerns that an H5 pandemic is imminent.

Cambios en las coberturas vacunales antigripales en España entre los años 2001 y 2003. Análisis por comunidades autónomas

OBJECTIVES

To evaluate changes in influenza vaccination coverage in Spain by autonomous communities between 2001 and 2003 and to compare the influenza vaccination coverage obtained in Spanish National Health Surveys (NHS) with other official sources.

METHODS

A total of 42,722 cases from the NHS for 2001 (n = 21,072) and 2003 (n = 21,650) were analyzed. All the cases corresponded to adults aged more than 15 years old. Both surveys are representative of the autonomous communities.

RESULTS

For the entire sample, vaccine coverages of 19.3% (95% CI, 18.8-19.8) and 22.1% (95% CI, 21.4-22.8) were estimated in 2001 and 2003 respectively. In the logit regression model adjusted by age, sex and associated chronic diseases, significant improvements were found in coverage in individuals aged more than 64 years (odds ratio = 1.26; 95% CI, 1.14-1.40) for Spain as a whole and for 6 autonomous communities between 2001 and 2003. For the group aged less than 65 years with associated chronic diseases, a significant improvement in coverage was found for Spain as a whole and for 3 autonomous communities.

CONCLUSIONS

Between 2001 and 2003, influenza vaccination coverage in the risk groups studied significantly improved in Spain and in several autonomous communities. The information on influenza vaccination coverage obtained in the Spanish National Health Surveys was similar to that found in the Autonomous Communities Health Surveys and in the Ministry of Health and Consumer Affairs.

The Efficacy of Vaccines to Prevent Infectious Diseases in the Elderly

Infectious diseases still represent a major challenge to human progress and survival. Especially elderly persons are more frequently and severely affected by infectious diseases and they display distinct features with respect to clinical presentation and treatment. Although vaccinations are considered a vital medical procedure for preventing morbidity and mortality caused by infectious diseases, the protective effect of vaccinations is abrogated in elderly persons. This is due to a decline in the functions of the immune system referred to as immunosenescence. The first part of this chapter will therefore summarize the status quo of the efficacy of vaccines in preventing morbidity and mortality caused by typical infectious diseases in the elderly, such as influenza, pneumonia and tuberculosis. The second part will then elucidate the underlying age-related mechanisms which may contribute to the decreased efficacy of vaccines. Based on the complex mechanisms involved in immunosenescence, strategies will be outlined which may be succesfful in enhancing protective immune responses following vaccination in elderly persons.

Alternative routes of influenza vaccine delivery

The global emergence of virulent avian influenza and the concomitant raised threat of an influenza pandemic has increased interest in the development of improved influenza vaccines. Whereas conventional influenza vaccines are delivered by parenteral injection, an intranasal influenza vaccine has been marketed since 2003. Many other technologies are in development for intranasal, oral, epidermal and topical influenza vaccines. This editorial summarises the advances in clinical development of technologies for needle-free influenza vaccine delivery.

The virosome concept for influenza vaccines

There is a need for more efficacious inactivated influenza vaccines, since current formulations show suboptimal immunogenicity in at-risk populations, like the elderly. More effective vaccines are also urgently needed for an improved influenza pandemic preparedness. In this context, there is considerable interest in virosomes. Virosomes are virus-like particles, consisting of reconstituted influenza virus envelopes, lacking the genetic material of the native virus. Virosomes are produced from influenza virus through a detergent solubilization and removal procedure. Properly reconstituted virosomes retain the cell binding and membrane fusion properties of the native virus, mediated by the viral envelope glycoprotein haemagglutinin. These functional characteristics of virosomes form the basis for their enhanced immunogenicity. First, the repetitive arrangement of haemagglutinin molecules on the virosomal surface mediates a cooperative interaction of the antigen with Ig receptors on B lymphocytes, stimulating strong antibody responses. In addition, virosomes interact efficiently with antigen-presenting cells, such as dendritic cells, resulting in activation of T lymphocytes. In a murine model system, virosomes, as compared to conventional subunit vaccine, which consists of isolated influenza envelope glycoproteins, induce a more balanced T helper 1 versus T helper 2 response, virosomes in particular eliciting stronger T helper 1 responses than subunit vaccine. Also, as a result of fusion of the virosomes with the endosomal membrane, part of the virosomal antigen gains access to the major histocompatibility class I presentation pathway, thus priming cytotoxic T lymphocyte activity. Finally, virosomes represent an excellent platform for inclusion of lipophilic adjuvants for further stimulation of vaccine immunogenicity. By virtue of these characteristics, virosomes represent a promising novel class of inactivated influenza vaccines, which not only induce high virus-neutralizing antibody titres, but also prime the cellular arm of the immune system.

Influenza: current threat from avian influenza

Influenza is an infectious respiratory pathogen causing annual outbreaks and infrequent pandemics, resulting in significant morbidity, mortality and burdens on the delivery of health care. The geographical spread of highly pathogenic avian influenza (HPAI) H5N1 among poultry and wild bird populations is unprecedented. Growing numbers of sporadic avian influenza infections are occurring in humans, increasing the threat of the next influenza pandemic. Vaccines are the principle means of combating influenza, and a number of studies with H5N1 vaccine candidates are underway. Antiviral agents can be used to treat influenza infection and can be taken as chemoprophylaxis during influenza outbreaks. Oseltamivir has been stockpiled as part of influenza pandemic preparedness planning; however, the emergence of drug resistance may limit its clinical use.