Virosomal influenza vaccine: a safe and effective influenza vaccine with high efficacy in elderly and subjects with low pre-vaccination antibody titers

A low dose of RBD and TLR7/8 agonist displayed on influenza virosome particles protects rhesus macaque against SARS-CoV-2 challenge

Influenza virosomes serve as antigen delivery vehicles and pre-existing immunity toward influenza improves the immune responses toward antigens. Here, vaccine efficacy was evaluated in non-human primates with a COVID-19 virosome-based vaccine containing a low dose of RBD protein (15 µg) and the adjuvant 3M-052 (1 µg), displayed together on virosomes. Vaccinated animals (n = 6) received two intramuscular administrations at week 0 and 4 and challenged with SARS-CoV-2 at week 8, together with unvaccinated control animals (n = 4). The vaccine was safe and well tolerated and serum RBD IgG antibodies were induced in all animals and in the nasal washes and bronchoalveolar lavages in the three youngest animals. All control animals became strongly sgRNA positive in BAL, while all vaccinated animals were protected, although the oldest vaccinated animal (V1) was transiently weakly positive. The three youngest animals had also no detectable sgRNA in nasal wash and throat. Cross-strain serum neutralizing antibodies toward Wuhan-like, Alpha, Beta, and Delta viruses were observed in animals with the highest serum titers. Pro-inflammatory cytokines IL-8, CXCL-10 and IL-6 were increased in BALs of infected control animals but not in vaccinated animals. Virosomes-RBD/3M-052 prevented severe SARS-CoV-2, as shown by a lower total lung inflammatory pathology score than control animals.

Virosome: An engineered virus for vaccine delivery

The purpose of immunization is the effective cellular and humoral immune response against antigens. Several studies on novel vaccine delivery approaches such as micro-particles, liposomes & nanoparticles, etc. against infectious diseases have been investigated so far. In contrast to the conventional approaches in vaccine development, a virosomes-based vaccine represents the next generation in the field of immunization because of its balance between efficacy and tolerability by virtue of its mechanism of immune instigation. The versatility of virosomes as a vaccine adjuvant, and delivery vehicle of molecules of different nature, such as peptides, nucleic acids, and proteins, as well as provide an insight into the prospect of drug targeting using virosomes. This article focuses on the basics of virosomes, structure, composition formulation and development, advantages, interplay with the immune system, current clinical status, different patents highlighting the applications of virosomes and their status, recent advances, and research associated with virosomes, the efficacy, safety, and tolerability of virosomes based vaccines and the future prospective.

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.

Vaccines for preventing influenza in the elderly

BACKGROUND

The consequences of influenza in the elderly (those age 65 years or older) are complications, hospitalisations, and death. The primary goal of influenza vaccination in the elderly is to reduce the risk of death among people who are most vulnerable. This is an update of a review published in 2010. Future updates of this review will be made only when new trials or vaccines become available. Observational data included in previous versions of the review have been retained for historical reasons but have not been updated because of their lack of influence on the review conclusions.

OBJECTIVES

To assess the effects (efficacy, effectiveness, and harm) of vaccines against influenza in the elderly.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (the Cochrane Library 2016, Issue 11), which includes the Cochrane Acute Respiratory Infections Group's Specialised Register; MEDLINE (1966 to 31 December 2016); Embase (1974 to 31 December 2016); Web of Science (1974 to 31 December 2016); CINAHL (1981 to 31 December 2016); LILACS (1982 to 31 December 2016); WHO International Clinical Trials Registry Platform (ICTRP; 1 July 2017); and ClinicalTrials.gov (1 July 2017).

SELECTION CRITERIA

Randomised controlled trials (RCTs) and quasi-RCTs assessing efficacy against influenza (laboratory-confirmed cases) or effectiveness against influenza-like illness (ILI) or safety. We considered any influenza vaccine given independently, in any dose, preparation, or time schedule, compared with placebo or with no intervention. Previous versions of this review included 67 cohort and case-control studies. The searches for these trial designs are no longer updated.

DATA COLLECTION AND ANALYSIS

Review authors independently assessed risk of bias and extracted data. We rated the certainty of evidence with GRADE for the key outcomes of influenza, ILI, complications (hospitalisation, pneumonia), and adverse events. We have presented aggregate control group risks to illustrate the effect in absolute terms. We used them as the basis for calculating the number needed to vaccinate to prevent one case of each event for influenza and ILI outcomes.

MAIN RESULTS

We identified eight RCTs (over 5000 participants), of which four assessed harms. The studies were conducted in community and residential care settings in Europe and the USA between 1965 and 2000. Risk of bias reduced our certainty in the findings for influenza and ILI, but not for other outcomes.Older adults receiving the influenza vaccine may experience less influenza over a single season compared with placebo, from 6% to 2.4% (risk ratio (RR) 0.42, 95% confidence interval (CI) 0.27 to 0.66; low-certainty evidence). We rated the evidence as low certainty due to uncertainty over how influenza was diagnosed. Older adults probably experience less ILI compared with those who do not receive a vaccination over the course of a single influenza season (3.5% versus 6%; RR 0.59, 95% CI 0.47 to 0.73; moderate-certainty evidence). These results indicate that 30 people would need to be vaccinated to prevent one person experiencing influenza, and 42 would need to be vaccinated to prevent one person having an ILI.The study providing data for mortality and pneumonia was underpowered to detect differences in these outcomes. There were 3 deaths from 522 participants in the vaccination arm and 1 death from 177 participants in the placebo arm, providing very low-certainty evidence for the effect on mortality (RR 1.02, 95% CI 0.11 to 9.72). No cases of pneumonia occurred in one study that reported this outcome (very low-certainty evidence). No data on hospitalisations were reported. Confidence intervaIs around the effect of vaccines on fever and nausea were wide, and we do not have enough information about these harms in older people (fever: 1.6% with placebo compared with 2.5% after vaccination (RR 1.57, 0.92 to 2.71; moderate-certainty evidence)); nausea (2.4% with placebo compared with 4.2% after vaccination (RR 1.75, 95% CI 0.74 to 4.12; low-certainty evidence)).

AUTHORS' CONCLUSIONS

Older adults receiving the influenza vaccine may have a lower risk of influenza (from 6% to 2.4%), and probably have a lower risk of ILI compared with those who do not receive a vaccination over the course of a single influenza season (from 6% to 3.5%). We are uncertain how big a difference these vaccines will make across different seasons. Very few deaths occurred, and no data on hospitalisation were reported. No cases of pneumonia occurred in one study that reported this outcome. We do not have enough information to assess harms relating to fever and nausea in this population.The evidence for a lower risk of influenza and ILI with vaccination is limited by biases in the design or conduct of the studies. Lack of detail regarding the methods used to confirm the diagnosis of influenza limits the applicability of this result. The available evidence relating to complications is of poor quality, insufficient, or old and provides no clear guidance for public health regarding the safety, efficacy, or effectiveness of influenza vaccines for people aged 65 years or older. Society should invest in research on a new generation of influenza vaccines for the elderly.

An H1-H3 chimeric influenza virosome confers complete protection against lethal challenge with PR8 (H1N1) and X47 (H3N2) viruses in mice

Annual health threats and economic damages caused by influenza virus are still a main concern of the World Health Organization and other health departments all over the world. An influenza virosome is a highly efficient immunomodulating carrier mimicking the natural antigen presentation pathway and has shown an excellent tolerability profile due to its biocompatibility and purity. The major purpose of this study was to construct a new chimeric virosome influenza vaccine containing hemagglutinin (HA) and neuraminidase (NA) proteins derived from the A/PR/8/1934 (H1N1) (PR8) and A/X/47 (H3N2) (X47) viruses, and to evaluate its efficacy as a vaccine candidate in mice. A single intramuscular vaccination with the chimeric virosomes provided complete protection against lethal challenge with the PR8 and X47 viruses. The chimeric virosomes induced high IgG antibody responses as well as hemagglutination inhibition (HAI) titers. HAI titers following the chimeric virosome vaccination were at the same level as the whole inactivated influenza vaccine. Mice immunized with the chimeric virosomes displayed considerably less weight loss and exhibited significantly reduced viral load in their lungs compared with the controls. The chimeric virosomes can be used as an innovative vaccine formulation to confer protection against a broad range of influenza viruses.

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 as vaccine adjuvant and carrier system

The basic concept of virosomes is the controlled in vitro assembly of virus-like particles from purified components. The first generation of influenza virosomes developed two decades ago is successfully applied in licensed vaccines, providing a solid clinical safety and efficacy track record for the technology. In the meantime, a second generation of influenza virosomes has evolved as a carrier and adjuvant system, which is currently applied in preclinical and clinical stage vaccine candidates targeting various prophylactic and therapeutic indications. The inclusion of additional components to optimize particle assembly, to stabilize the formulations, or to enhance the immunostimulatory properties have further improved and broadened the applicability of the platform.

Targeted vaccine selection in influenza vaccination

BACKGROUND

The main target groups for influenza vaccination are the elderly, the chronically ill, infants, and toddlers. Influenza vaccines are needed that suit the immunological particularities of each of these age and risk groups. Recent years have seen the approval of influenza vaccines that are more immunogenic than before, but whose use in Germany is limited by the restriction of reimbursement to a small number of vaccines.

METHODS

The Medline database was selectively searched for pertinent literature.

RESULTS

The suboptimal immunogenicity of conventional influenza vaccines that contain inactivated viral cleavage products and subunits can be markedly improved by the use of squalene-based adjuvant systems, by the integration of viral antigens in virosomal particles, or by intradermal administration. The vaccination of elderly persons with a vaccine containing the adjuvant MF59 was found to lower the risk of hospitalization for influenza or pneumonia by 25% compared to vaccination with a trivalent inactivated vaccine (TIV). On the other hand, the adjuvant ASO3 was found to be associated with an up to 17-fold increase in the frequency of narcolepsy among 4- to 18-year-olds. In a prospective study, a virosomal vaccine lowered the frequency of laboratory-confirmed influenza in vaccinated children by 88% compared to unvaccinated children (2 versus 18 cases per 1000 individuals). A live, attenuated influenza vaccine lowered the rate of disease in children up to age 7 by 48% compared to a TIV (4.2% versus 8.1%).

CONCLUSION

The newer vaccines possess improved efficacy when used for primary and booster immunization in certain age and risk groups, and they are superior in this respect to conventional vaccines based on viral cleavage products and subunits. The risk/benefit profiles of all currently available vaccines vary depending on the age group or risk group in which they are used.

A colorimetric assay for determination of residual detergent levels in reconstituted membrane protein preparations

Simple and robust methods for the quantification of residual detergent in purified membrane proteins are not readily available. In this article, solubilization of precipitated dye by detergent is shown to be a facile method for the quantification of residual levels of octaethylene-glycol-mono(n-dodecyl)ether in virosomal influenza vaccine. Dye solubilization starts in the critical micellar concentration range. The method is more sensitive than an existing assay and is highly accurate and precise. The method is applicable to other detergents as well. This method of residual detergent quantification is simple and straightforward and is a useful tool for quality control of subunit vaccines.

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.

Enhancement of immunogenicity of a virosome-based avian influenza vaccine in chickens by incorporating CpG-ODN

Influenza virosomes are virus-like particles, representing a platform for vaccine development. In this study, we examined the immunogenicity of avian influenza virosomes with or without inclusion of recombinant chicken interferon-gamma (rChIFN-γ) or CpG-ODN in chickens. Immunization with virosomes adjuvanted with CpG-ODN elicited the highest haemagglutination inhibition antibody titres, as well as IgG and IgA serum antibody responses. Moreover, Virosomes+CpG-ODN formulation induced an antigen-specific spleen cell proliferation and IFN-γ expression. In conclusion, our results demonstrated that virus-specific antibody- and cell-mediated responses may be induced in chickens immunized with virosomes and these responses can be enhanced by incorporating CpG-ODN in the virosome vaccine formulation.

Development and strategies of cell-culture technology for influenza vaccine

Influenza is a pandemic contagious disease and causes human deaths and huge economic destruction of poultry in the world. In order to control and prevent influenza, mainly type A, influenza vaccine for human and poultry were available since the 1940s and 1920s, respectively. In the development of vaccine production, influenza viruses were cultured originally from chicken embryos to anchorage-dependent cell lines, such as MDCK and Vero. The anchorage-independent lines have also been used to produce influenza virus, such as PER.C6 and engineering modified MDCK and Vero. During the process of influenza vaccine production, the common problem faced by all producers is how to improve the titer of influenza virus. This paper focuses on the developments of cell culture for influenza virus vaccine production, limitations of cell culture, and relative strategies for improvement virus yields in cell-culture systems.

Immunogenicity and tolerability of a virosome influenza vaccine compared to split influenza vaccine in patients with sickle cell anemia

The immunogenicity and tolerability of virosome and of split influenza vaccines in patients with sickle cell anemia (SS) were evaluated. Ninety SS patients from 8 to 34 years old were randomly assigned to receive either virosome (n=43) or split vaccine (n=47). Two blood samples were collected, one before and one 4-6 weeks after vaccination. Antibodies against viral strains (2006) A/New Caledonia (H1N1), A/California (H3N2), B/Malaysia were determined using the hemagglutinin inhibition test. Post-vaccine reactions were recorded over 7 days. Seroconversion rates for H1N1, H3N2 and B were 65.1%, 60.4% and 83.7% for virosome vaccine, and 68.0%, 61.7% and 68.0% for split vaccine. Seroprotection rates for H1N1, H3N2 e B were 100%, 97.6% and 69.7% for virosome, and 97.8%, 97.8% and 76.6% for split vaccine. No severe adverse reactions were recorded. Virosome and split vaccines in patients with sickle cell anemia were equally immunogenic, with high seroconversion and seroprotection rates. Both vaccines were well tolerated.

Vaccines for preventing influenza in the elderly

BACKGROUND

Vaccines have been the main global weapon to minimise the impact of influenza in the elderly for the last four decades and are recommended worldwide for individuals aged 65 years or older. The primary goal of influenza vaccination in the elderly is to reduce the risk of complications among persons who are most vulnerable.

OBJECTIVES

To assess the effectiveness of vaccines in preventing influenza, influenza-like illness (ILI), hospital admissions, complications and mortality in the elderly. To identify and appraise comparative studies evaluating the effects of influenza vaccines in the elderly. To document types and frequency of adverse effects associated with influenza vaccines in the elderly.

SEARCH STRATEGY

We searched the Cochrane Central Register of Controlled Trials (CENTRAL), which contains the Cochrane Acute Respiratory Infections (ARI) Group's Specialised Register (The Cochrane Library 2009, issue 4); MEDLINE (January 1966 to October Week 1 2009); EMBASE (1974 to October 2009) and Web of Science (1974 to October 2009).

SELECTION CRITERIA

Randomised controlled trials (RCTs), quasi-RCTs, cohort and case-control studies assessing efficacy against influenza (laboratory-confirmed cases) or effectiveness against influenza-like illness (ILI) or safety. Any influenza vaccine given independently, in any dose, preparation or time schedule, compared with placebo or with no intervention was considered.

DATA COLLECTION AND ANALYSIS

We grouped reports first according to the setting of the study (community or long-term care facilities) and then by level of viral circulation and vaccine matching. We further stratified by co-administration of pneumococcal polysaccharide vaccine (PPV) and by different types of influenza vaccines. We analysed the following outcomes: influenza, influenza-like illness, hospital admissions, complications and deaths.

MAIN RESULTS

We included 75 studies. Overall we identified 100 data sets. We identified one RCT assessing efficacy and effectiveness. Although this seemed to show an effect against influenza symptoms it was underpowered to detect any effect on complications (1348 participants). The remainder of our evidence base included non-RCTs. Due to the general low quality of non-RCTs and the likely presence of biases, which make interpretation of these data difficult and any firm conclusions potentially misleading, we were unable to reach clear conclusions about the effects of the vaccines in the elderly.

AUTHORS' CONCLUSIONS

The available evidence is of poor quality and provides no guidance regarding the safety, efficacy or effectiveness of influenza vaccines for people aged 65 years or older. To resolve the uncertainty, an adequately powered publicly-funded randomised, placebo-controlled trial run over several seasons should be undertaken.

Pseudovirions as vehicles for the delivery of siRNA

Over the last two decades, small interfering RNA (siRNA)-mediated gene silencing has quickly become one of the most powerful techniques used to study gene function in vitro and a promising area for new therapeutics. Delivery remains a significant impediment to realizing the therapeutic potential of siRNA, a problem that is also tied to immunogenicity and toxicity. Numerous delivery vehicles have been developed, including some that can be categorized as pseudovirions: these are vectors that are directly derived from viruses but whose viral coding sequences have been eliminated, preventing their classification as viral vectors. Characteristics of the pseudovirions discussed in this review, namely phagemids, HSV amplicons, SV40 in vitro-packaged vectors, influenza virosomes, and HVJ-Envelope vectors, make them attractive for the delivery of siRNA-based therapeutics. Pseudovirions were shown to deliver siRNA effector molecules and bring about RNA interference (RNAi) in various cell types in vitro, and in vivo using immune-deficient and immune-competent mouse models. Levels of silencing were not always determined directly, but the duration of siRNA-induced knockdown lasted at least 3 days. We present examples of the use of pseudovirions for the delivery of synthetic siRNA as well as the delivery and expression of DNA-directed siRNA.

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.

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.

Emerging vaccines for influenza

BACKGROUND

Influenza remains one of the leading causes of morbidity and mortality worldwide. The available vaccines are least effective in the populations at greatest risk--children, the elderly, and the immunocompromised. Furthermore, avian influenza and other novel strains have the potential to cause the next influenza pandemic. Research efforts have accelerated worldwide to develop new vaccines to provide better immunity against annual epidemics and a potential pandemic.

OBJECTIVE

To summarize the global research efforts at developing new influenza vaccines, adjuvants, and delivery devices.

METHOD

MEDLINE and Pharmaprojects databases were searched for publications and continuing research on new influenza vaccine technologies.

RESULTS/CONCLUSIONS

Technologies such as DNA vaccines, live recombinant viral vector vaccines, and virus-like particles have shown significant promise for immunogenicity and protection from experimental challenge to influenza. New modalities for vaccine delivery and methods for rapid vaccine production are also being investigated. With the possibility of an influenza pandemic increasing the need to develop new vaccines, the global research community has made large strides to meet this challenge.

Safety and immunogenicity of two influenza virus subunit vaccines, with or without MF59 adjuvant, administered to human immunodeficiency virus type 1-seropositive and -seronegative adults

The objective of this study was to evaluate and compare both the safety and tolerability and the humoral and cell-mediated immune responses for two influenza virus subunit vaccines, one with MF59 adjuvant (Fluad) and one without an adjuvant (Agrippal), in healthy and in human immunodeficiency virus type 1 (HIV-1)-infected adult individuals. To achieve this aim, an open, randomized, comparative clinical trial was performed during the 2005-2006 season. A total of 256 subjects were enrolled to receive one dose of vaccine intramuscularly. Blood samples were taken at the time of vaccination and at 1 and 3 months postvaccination. A good humoral antibody response was detected for both vaccines, meeting all the criteria of the Committee for Medical Products for Human Use. After Beyer's correction for prevaccination status, Fluad exhibited better immunogenicity than Agrippal, as shown from the analysis of the geometric mean titers, with significant differences for some virus strains; however, no definitive conclusions on the clinical significance of such results can be drawn, because the method used to estimate antibody response is currently nonstandard for influenza virus vaccines. Significant induction of an antigen-specific CD4+ T-lymphocyte proliferative response was detected at all time points after immunization, for both the vaccines, among HIV-1-seronegative subjects. This was different from what was observed for HIV-1-infected individuals. In this group, significance was not reached at 30 days postvaccination (T30) for those immunized with Agrippal. Also when data were compared between treatment groups, a clear difference in the response at T30 was observed in favor of Fluad (P = 0.0002). The safety profiles of both vaccines were excellent. For HIV-1-infected individuals, no significant changes either in viremia or in the CD4+ cell count were observed at any time point. The results showed good safety and immunogenicity for both vaccines under study for both uninfected and HIV-1-infected adults, confirming current recommendations for immunization of this high-risk category.

Immunosupportive therapies in aging

The primary role of the immune system is to protect the organism against pathogens, but age-associated alterations to immunity increase the susceptibility of the elderly to infectious disease. The exact nature of these changes is still controversial, but the use of screening procedures, such as the SENIEUR protocol to exclude underlying illness, helped to better characterize the changes actually related to physiological aging rather than pathology. It is generally agreed that the most marked changes occur in the cellular immune response reflecting profound alterations in T cells. Much of this is due to thymic involution as well as changes in the proportions of T cell subpopulations resulting from antigen exposure, and altered T cell activation pathways. However, a body of data indicates that innate immune responses, including the critical bridge between innate and adaptive immunity, and antigen presenting capacity are not completely resistant to senescence processes. The consequences of all these alterations are an increased incidence of infections, as well as possibly cancers, autoimmune disorders, and chronic inflammatory diseases. The leading question is what, if anything, can we do to prevent these deleterious changes without dangerously dysregulating the precarious balance of productive immunity versus immunopathology? There are many potential new therapeutic means now available to modulate immunosenescence and many others are expected to be available shortly. One main problem in applying these experimental therapies is ethical: there is a common feeling that as ageing is not a disease; the elderly are not sick and therefore do not require adventurous therapies with unpredictable side-effects in mostly frail individuals. Animal models are not helpful in this context. In this chapter we will first briefly review what we think we know about human immunosenescence and its consequences for the health status of elderly individuals. We will then discuss possible interventions that might one day become applicable in an appropriate ethical environment.

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.

Fitness costs limit escape from cytotoxic T lymphocytes by influenza A viruses

The use of cytotoxic T lymphocyte (CTL)-inducing vaccines could afford both homo- and heterosubtypic immunity. However, amino acid variation in CTL epitopes associated with escape from CTL-mediated immunity might undermine the use of these vaccines. To assess the impact of amino acid substitutions in highly conserved epitopes on viral fitness and recognition by specific CTL, we performed a mutational analysis of various CTL epitopes. Our findings indicated that fitness costs limited variation in functionally constrained epitopes, especially at anchor residues.

Vaccines for preventing influenza in the elderly

BACKGROUND

Influenza vaccination of elderly individuals is recommended worldwide and has been targeted toward the elderly and those at serious risk of complications.

OBJECTIVES

Our aim was to review the evidence of efficacy, effectiveness and safety of influenza vaccines in individuals aged 65 years or older.

SEARCH STRATEGY

We searched the following databases on The Cochrane Library, the Cochrane Central Register of Controlled Trials (CENTRAL), the Cochrane Database of Systematic Reviews, and the Database of Abstracts of Reviews of Effectiveness (Issue 1, 2006); MEDLINE (January 1966 to March Week 3 2006); EMBASE (Dialog 1974 to 1979; SilverPlatter 1980 to December 2005); Biological Abstracts (SilverPlatter 1969 to December 2004); and Science Citation Index (Web of Science 1974 to December 2004).

SELECTION CRITERIA

We considered randomised, quasi-randomised, cohort and case-control studies assessing efficacy against influenza (laboratory-confirmed cases) or effectiveness against influenza-like illness (ILI) or safety. Any influenza vaccine given independently, in any dose, preparation or time schedule, compared with placebo or with no intervention was considered.

DATA COLLECTION AND ANALYSIS

We grouped reports first according to the setting of the study (community or long-term care facilities) and then by level of viral circulation and vaccine matching. We further stratified by co-administration of pneumococcal polysaccharide vaccine (PPV) and by different types of influenza vaccines. We analysed the following outcomes: influenza, influenza-like illness, hospital admissions, complications and deaths.

MAIN RESULTS

Sixty-four studies were included in the efficacy / effectiveness assessment, resulting in 96 data sets. In homes for elderly individuals (with good vaccine match and high viral circulation) the effectiveness of vaccines against ILI was 23% (6% to 36%) and non-significant against influenza (RR 1.04: 95% CI 0.43 to 2.51). We found no correlation between vaccine coverage and ILI attack rate. Well matched vaccines prevented pneumonia (VE 46%; 30% to 58%), hospital admission (VE 45%; 16% to 64%) and deaths from influenza or pneumonia (VE 42%, 17% to 59%). In elderly individuals living in the community, vaccines were not significantly effective against influenza (RR 0.19; 95% CI 0.02 to 2.01), ILI (RR 1.05: 95% CI 0.58 to 1.89), or pneumonia (RR 0.88; 95% CI 0.64 to 1.20). Well matched vaccines prevented hospital admission for influenza and pneumonia (VE 26%; 12% to 38%) and all-cause mortality (VE 42%; 24% to 55%). After adjustment for confounders, vaccine performance was improved for admissions to hospital for influenza or pneumonia (VE* 27%; 21% to 33%), respiratory diseases (VE* 22%; 15% to 28%) and cardiac disease (VE* 24%; 18% to 30%); and for all-cause mortality (VE* 47%; 39% to 54%). The public health safety profiles of the vaccines appear to be acceptable.

AUTHORS' CONCLUSIONS

In long-term care facilities, where vaccination is most effective against complications, the aims of the vaccination campaign are fulfilled, at least in part. However, according to reliable evidence the usefulness of vaccines in the community is modest. The apparent high effectiveness of the vaccines in preventing death from all causes may reflect a baseline imbalance in health status and other systematic differences in the two groups of participants.

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.

Clinical experience with inactivated, virosomal influenza vaccine

Current available influenza vaccines are safe and effective in preventing influenza. Nevertheless, there is a need for influenza vaccines with improved efficacy in the elderly. This need is underscored by both the observation that influenza has a major clinical and economic impact in the elderly and the fact that currently available vaccines are generally less effective in elderly than in younger subjects. Several approaches are currently being pursued in order to improve the efficacy of influenza vaccines in elderly individuals and others who have impaired immune responses to conventional influenza vaccines. A novel antigen-presenting strategy to overcome impaired immune responses is the use of virosomes. Previously, data on safety and reactogenicity have been published regarding the use of virosomal influenza vaccines. Data from three recent clinical trials are presented here. The first of these was a comparative study of a virosomal vaccine and a conventional subunit vaccine in "at-risk" adults with underlying chronic illness. The virosomal vaccine demonstrated comparable tolerability to the subunit vaccine, with about 98% of patients reporting tolerability to be good or very good. The vast majority of adverse events reported were mild to moderate in severity. With both vaccine types, mean HI titres decreased with age for both the A-H1N1 and B influenza virus strains, but for the A-H3N2 strain (the most virulent of the three strains), mean HI titres did not decrease with age, suggesting a better response with the virosomal vaccine when compared to the subunit vaccine. All three studies explored the long-term persistence of antibodies after vaccination with virosomal influenza vaccines. Immunogenicity declined over time but remained high at 4, 6 and 12 months post-vaccination compared to baseline, indicating that adequate seroprotection is achievable for the duration of the influenza season. Virosomal vaccines may induce better immunity in elderly subjects and may be more effective in reducing morbidity and mortality in this age group.

Influenza: current evidence and informed predictions

Every winter there are sharp rises in medical visits, hospitalizations and deaths from acute respiratory illness worldwide. Influenza is an important cause of these and is the only common viral respiratory pathogen with licensed vaccines available that are safe and effective in preventing disease. Over 50 countries have national vaccination programs focusing on the elderly population and those at high risk. In the USA, healthy children are also now offered the vaccine; routine immunization of the young, who are similarly vulnerable to hospitalization as the old, is likely to become universal. There remains a need for further improvement in vaccine effectiveness (both in the short- and long-term), vaccine administration and compliance. Recent technological developments raise the prospect of using new vaccine types, such as live attenuated and Vero cell-cultured vaccines, that are easier to administer and may induce broader immunity.