An MF59-adjuvanted inactivated influenza vaccine containing A/Panama/1999 (H3N2) induced broader serological protection against heterovariant influenza virus strain A/Fujian/2002 than a subunit and a split influenza vaccine

MF59™ as a vaccine adjuvant: a review of safety and immunogenicity

Approximately 70 years passed between the licensing of alum salts as vaccine adjuvants and that of MF59™ MF59, an oil-in-water emulsion, is currently licensed for use in the elderly as an adjuvant in seasonal influenza vaccines. Its mechanism of action is not fully understood, but enhancement of the interaction between the antigen and the dendritic cell seems to be involved. When used with seasonal influenza vaccines, an increase occurs in the hemagglutination inhibition antibody titers against some, but not all, seasonal vaccine influenza strains. The adjuvant effect is more pronounced when MF59 is combined with novel influenza antigens such as H9 and H5. The use of the adjuvant is associated with an increase in the frequency of local and systemic early post-vaccine adverse events (3-7 days), but no increase in adverse events was observed thereafter. Currently, MF59 is under evaluation as an adjuvant with other antigens such as pandemic influenza antigens and cytomegalovirus antigens.

Unmet needs in modern vaccinology: adjuvants to improve the immune response

The key objective of vaccination is the induction of an effective pathogen-specific immune response that leads to protection against infection and/or disease caused by that pathogen, and that may ultimately result in its eradication from humanity. The concept that the immune response to pathogen antigens can be improved by the addition of certain compounds into the vaccine formulation was demonstrated about one hundred years ago when aluminium salts were introduced. New vaccine technology has led to vaccines containing highly purified antigens with improved tolerability and safety profiles, but the immune response they induce is suboptimal without the help of adjuvants. In parallel, the development of effective vaccines has been facing more and more important challenges linked to complicated pathogens (e.g. malaria, TB, HIV, etc.) and/or to subjects with conditions that jeopardize the induction or persistence of a protective immune response. A greater understanding of innate and adaptive immunity and their close interaction at the molecular level is yielding insights into the possibility of selectively stimulating immunological pathways to obtain the desired immune response. The better understanding of the mechanism of 'immunogenicity' and 'adjuvanticity' has prompted the research of new vaccine design based on new technologies, such as naked DNA or live vector vaccines and the new adjuvant approaches. Adjuvants can be used to enhance the magnitude and affect the type of the antigen-specific immune response, and the combination of antigens with more than one adjuvant, the so called adjuvant system approach, has been shown to allow the development of vaccines with the ability to generate effective immune responses adapted to both the pathogen and the target population. This review focuses on the adjuvants and adjuvant systems currently in use in vaccines, future applications, and the remaining challenges the field is facing.

Factors that may impact on immunosenescence: an appraisal

The increasing ratio of ageing population poses new challenges to healthcare systems. The elderly frequently suffer from severe infections. Vaccination could protect them against several infectious diseases, but it can be effective only if cells that are capable of responding are still present in the repertoire. Recent vaccination strategies in the elderly might achieve low effectiveness due to age-related immune impairment. Immunosenescence affects both the innate and adaptive immunity.Beside individual variations of genetic predisposition, epigenetic changes over the full course of human life exert immunomodulating effects. Disturbances in macrophage-derived cytokine release and reduction of the natural killer cell mediated cytotoxicity lead to increased frequency of infections. Ageing dampens the ability of B cells to produce antibodies against novel antigens. Exhausted memory B lymphocyte subsets replace naïve cells. Decline of cell-mediated immunity is the consequence of multiple changes, including thymic atrophy, reduced output of new T lymphocytes, accumulation of anergic memory cells, and deficiencies in cytokines production. Persistent viral and parasitic infections contribute to the loss of immunosurveillance and premature exhaustion of T cells. Reduced telomerase activity and Toll-like receptor expression can be improved by chemotherapy. Reversion of thymic atrophy could be achieved by thymus transplantation, depletion of accumulated dysfunctional naive T cells and herpesvirus-specific exhausted memory cells. Administration of interleukin (IL)-2, IL-7, IL-10, keratinocyte growth factor, thymic stromal lymphopoietin, as well as leptin and growth hormone boost thymopoiesis. In animals, several strategies have been explored to produce superior vaccines. Among them, virosomal vaccines containing polypeptide antigens or DNA plasmids as well as new adjuvanted vaccine formulations elicit higher dendritic cell activity and more effective serologic than conventional vaccines responses in the elderly. Hopefully, at least some of these approaches can be translated to human medicine in a not too far future.

Antibody response against heterogeneous circulating influenza virus strains elicited by MF59- and non-adjuvanted vaccines during seasons with good or partial matching between vaccine strain and clinical isolates

MF59 is already known to enhance the breadth of antibody response to mismatched influenza seasonal and avian strains. However, little is known on the effect of MF59 on immunogenicity of influenza vaccines when "apparent" good matching between circulating and vaccine strains exists. To this end, we compared the immune response elicited by MF59-adjuvanted or non-adjuvanted subunit vaccine, containing A/California/7/04(H3N2) strain, against circulating viruses isolated between 2004/2005 and 2006/2007 seasons, belonging to different clades. The advantage offered by MF59 in terms of higher immunogenicity, expressed as higher post-vaccination HI titres, is observable also against viruses showing antigenic and molecular pattern undistinguishable from vaccine strain, but it became even more evident as the antigenic and molecular distance between vaccine and circulating strains grew. These data show that seasonal influenza vaccine adjuvanted with MF59 can offer a stronger benefit as compared to non-adjuvanted vaccine in protecting against a broader range of virus strains circulating during the influenza season.

Immune mechanisms of protection: can adjuvants rise to the challenge?

For many diseases vaccines are lacking or only partly effective. Research on protective immunity and adjuvants that generate vigorous immune responses may help generate effective vaccines against such pathogens.

Immunogenicity of three different influenza vaccines against homologous and heterologous strains in nursing home elderly residents

We studied whether MF59-adjuvanted influenza vaccine improves immunity against drifted influenza strains in institutionalised elderly with underling chronic health conditions. Sera from a randomized study, comparing MF59-adjuvanted (Sub/MF59, n = 72), virosomal (SVV, n = 39), and split (n = 88) vaccines, were retested using a hemagglutination inhibition (HI) assay against homologous (Northern Hemisphere [NH] 1998/99) and drifted (NH 2006/07) strains. Corrected postvaccination HI antibody titres were significantly higher with Sub/MF59 than SVV for all strains; GMTs against homologous A/H3N2 and B and both drifted A strains were significantly higher for Sub/MF59 than split. Seroprotection rates and mean-fold titer increases were generally higher with Sub/MF59 for all A influenza strains. MF59-adjuvanted influenza vaccine induced greater and broader immune responses in elderly people with chronic conditions, than conventional virosomal and split vaccines, particularly for A/H1 and A/H3 strains, potentially giving clinical benefit in seasons where antigenic mismatch occurs.

Immunosenescence and vaccination of the elderly II. New strategies to restore age-related immune impairment

One of the greatest health-care challenges in the elderly is to ensure that vaccination against infections are optimally effective, but vaccination can only be effective if cells that are capable of responding are still present in the repertoire. The reversing of immunosenescence could be achieved by improving immune responses or altering vaccine formulation. Recent vaccination strategies in the elderly exert low effectiveness. Nutritional interventions and moderate exercise delay T cell senescence. Telomerase activity and expression of toll-like receptors can be improved by chemotherapy. Reversion of thymic atrophy could be achieved by thymus transplantation, depletion of accumulated dysfunctional naive T cells and herpesvirus-specific exhausted memory cells. Administration of immunostimulatory and anti-inflammatory cytokines show the best practical approach. Reduced dendritic cell activity and co-receptor expression might be increased by interleukin (IL)-2 administration. IL-7 protects both B and T lymphocytes, but IL-2, IL-10, keratinocyte growth factor, thymic stromal lymphopoietin, as well as leptin and growth hormone also have a stimulatory effect on thymopoiesis. In animals, several strategies have been explored to produce more efficacious vaccines including high dose vaccines, DNA vaccines with immunostimulatory patch, virosomal vaccines and vaccines containing new adjuvants. Hopefully, one of these approaches will be translated into human therapy in a short time.

Influenza vaccine administration in rheumatoid arthritis patients under treatment with TNFalpha blockers: safety and immunogenicity

Twenty-eight patients with low-moderate, stable rheumatoid arthritis (RA), under treatment with tumor necrosis factor (TNF) alpha blockers, were immunized at least once with non-adjuvanted trivalent influenza vaccine during three consecutive influenza seasons. Antibodies toward A influenza antigens significantly increased and reached protective levels, still detectable 6 months after vaccination, both in RA patients and healthy controls. Response to B antigen instead was only observed from the second year for healthy controls and in the third year for patients. No significant difference in disease activity and anti-nuclear antibodies was observed as a consequence of vaccine administration, whereas T regulatory cells showed a significant increase 30 days after immunization in RA patients. This study confirms safety of influenza vaccine administration in RA patients treated with TNFalpha blockers. The cohort follow-up revealed the overcoming of poor B vaccine antigen immunogenicity via repeated vaccinations. Finally, protective antibody response was still observed 6 months after vaccination.

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.

Enhanced immunogenicity of seasonal influenza vaccines in young children using MF59 adjuvant

BACKGROUND

Children have high morbidity and hospitalization rates from seasonal influenza. Meta-analyses suggest that conventional inactivated influenza vaccines are of low efficacy in young children, making vaccines that induce greater and broader immune protection in this vulnerable population a medical priority. Adjuvanted influenza vaccines may offer a solution.

SUBJECTS AND METHODS

Unprimed healthy children (6 to <36 months) were enrolled in an observer-blinded study and randomly assigned to receive 2 doses of MF59-adjuvanted vaccine (Sub/MF59, n = 130) or nonadjuvanted split vaccine (split, n = 139); subgroups of these (n = 43 and 46, respectively) received a booster dose 1 year later. Safety and clinical tolerability were assessed after each dose. Hemagglutination inhibition antibody titers were measured against influenza A and B strains included in the formulation of the vaccines and against mismatched strains.

RESULTS

Clinical tolerability and safety were generally comparable between vaccine groups, though some transient, mild solicited reactions were more frequent in the Sub/MF59 group. Postvaccination hemagglutination inhibition antibody titers to all 3 vaccine strains were significantly higher with Sub/MF59 than with split vaccine (all comparisons P < 0.001) after each of the 3 vaccine doses. In addition, Sub/MF59 induced significantly higher cross-reactivity against A/H3N2 and A/H1N1 mismatched strains.

CONCLUSION

MF59-adjuvanted influenza vaccine was well tolerated in healthy young children after each of 3 doses and induced greater, longer-lasting, and broader immune responses than a nonadjuvanted split vaccine. The enhanced immunogenicity of the adjuvanted vaccine was most evident in very young children and for the B vaccine strain.

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.

MF59-adjuvanted vaccines for seasonal and pandemic influenza prophylaxis

Abstract  Influenza is a major cause of worldwide morbidity and mortality through frequent seasonal epidemics and infrequent pandemics. Morbidity and mortality rates from seasonal influenza are highest in the most frail, such as the elderly, those with underlying chronic conditions and very young children. Antigenic mismatch between strains recommended for vaccine formulation and circulating viruses can further reduce vaccine efficacy in these populations. Seasonal influenza vaccines with enhanced, cross‐reactive immunogenicity are needed to address these problems and can confer a better immune protection, particularly in seasons were antigenic mismatch occurs. A related issue for vaccine development is the growing threat of pandemic influenza caused by H5N1 avian strains. Vaccines against strains with pandemic potential offer the best approach for reducing the potential impact of a pandemic. However, current non‐adjuvanted pre‐pandemic vaccines offer suboptimal immunogenicity against H5N1. For both seasonal and pre‐pandemic vaccines, the addition of adjuvants may be the best approach for providing enhanced cross‐reactive immunogenicity. MF59^®, the first oil‐in‐water emulsion licensed as an adjuvant for human use, can enhance vaccine immune responses through multiple mechanisms. A trivalent MF59‐adjuvanted seasonal influenza vaccine (Fluad^®) has shown to induce significantly higher immune responses to influenza vaccination in the elderly, compared with non‐adjuvanted vaccines, and to provide cross‐reactive immunity against divergent influenza strains. Similar results have been generated with a MF59‐adjuvanted H5N1 pre‐pandemic vaccine, which showed higher and broader immunogenicity compared with non‐adjuvanted pre‐pandemic vaccines.

Development of a vaccine against pandemic influenza viruses: current status and perspectives

The constant threat of a new influenza pandemic, which may be caused by a highly pathogenic avian influenza virus, necessitates the development of a vaccine capable of providing efficient, long-term, and cost-effective protection. Proven avenues for the development of vaccines against seasonal influenza as well as novel approaches have been explored over the past decade. Whereas significant insights are consistently being made, the generation of a highly efficient and cross-protective vaccine against the future pandemic influenza strain remains as the ultimate goal in the field. In this review, we re-examine these efforts and outline the scientific, political, and economic problems that befall this area of biotechnological research.

MF59-adjuvanted H5N1 vaccine induces immunologic memory and heterotypic antibody responses in non-elderly and elderly adults

BACKGROUND

Pathogenic avian influenza virus (H5N1) has the potential to cause a major global pandemic in humans. Safe and effective vaccines that induce immunologic memory and broad heterotypic response are needed.

METHODS AND FINDINGS

Healthy adults aged 18-60 and > 60 years (n = 313 and n = 173, respectively) were randomized (1:1) to receive two primary and one booster injection of 7.5 microg or 15 microg doses of a subunit MF59-adjuvanted H5N1 (A/Vietnam/1194/2004) (clade 1) vaccine. Safety was monitored until 6 months after booster. Immunogenicity was assessed by hemagglutination inhibition (HI), single radial hemolysis (SRH) and microneutralization assays (MN). Mild injection-site pain was the most common adverse reaction. No serious adverse events relating to the vaccine were reported. The humoral immune responses to 7.5 microg and 15 microg doses were comparable. The rates for seroprotection (HI>40; SRH>25 mm(2); MN > or = 40) after the primary vaccination ranged 72-87%. Six months after primary vaccination with the 7.5 microg dose, 18% and 21% of non-elderly and elderly adults were seroprotected; rates increased to 90% and 84%, respectively, after the booster vaccination. In the 15 microg group, seroprotection rates among non-elderly and elderly adults increased from 25% and 62% after primary vaccination to 92% and 88% after booster vaccination, respectively. A heterologous immune response to the H5N1/turkey/Turkey/05 strain was elicited after second and booster vaccinations.

CONCLUSIONS

Both formulations of MF59-adjuvanted influenza H5N1 vaccine were well tolerated. The European Union requirement for licensure for pre-pandemic vaccines was met by the lower dose tested. The presence of cross-reactive antibodies to a clade 2 heterologous strain demonstrates that this vaccine may be appropriate for pre-pandemic programs.

TRIAL REGISTRATION

(ClinicalTrials.gov) NCT00311480.

Influenza vaccination in the elderly: seeking new correlates of protection and improved vaccines

Influenza is foremost among all infectious diseases for an age-related increase in risk for serious complications and death. Determining the benefit of current influenza vaccines is largely limited to epidemiologic studies, since placebo-controlled trials of influenza vaccines are no longer considered ethical in the older adult population. Vaccine effectiveness is calculated from the relative reduction in influenza outcomes in individuals who elect to be vaccinated compared with those who do not, the assumptions for which are diverse and have led to considerable controversy as to the exact benefit of influenza vaccination in older adults. In spite of this controversy, there is no doubt that new influenza vaccine technologies are needed to improve protection and reverse the trend of rising hospitalization and death rates related to influenza in older adults despite widespread influenza vaccination programs. This article will review the challenges to new vaccine development, explore the potential correlates of protection against influenza, and describe how new vaccine technologies may improve protection against complicated influenza illness in the older adult population.

Vaccine adjuvant systems: enhancing the efficacy of sub-unit protein antigens

Vaccination remains a key tool in the protection and eradication of diseases. However, the development of new safe and effective vaccines is not easy. Various live organism based vaccines currently licensed, exhibit high efficacy; however, this benefit is associated with risk, due to the adverse reactions found with these vaccines. Therefore, in the development of vaccines, the associated risk-benefit issues need to be addressed. Sub-unit proteins offer a much safer alternative; however, their efficacy is low. The use of adjuvanted systems have proven to enhance the immunogenicity of these sub-unit vaccines through protection (i.e. preventing degradation of the antigen in vivo) and enhanced targeting of these antigens to professional antigen-presenting cells. Understanding of the immunological implications of the related disease will enable validation for the design and development of potential adjuvant systems. Novel adjuvant research involves the combination of both pharmaceutical analysis accompanied by detailed immunological investigations, whereby, pharmaceutically designed adjuvants are driven by an increased understanding of mechanisms of adjuvant activity, largely facilitated by description of highly specific innate immune recognition of components usually associated with the presence of invading bacteria or virus. The majority of pharmaceutical based adjuvants currently being investigated are particulate based delivery systems, such as liposome formulations. As an adjuvant, liposomes have been shown to enhance immunity against the associated disease particularly when a cationic lipid is used within the formulation. In addition, the inclusion of components such as immunomodulators, further enhance immunity. Within this review, the use and application of effective adjuvants is investigated, with particular emphasis on liposomal-based systems. The mechanisms of adjuvant activity, analysis of complex immunological characteristics and formulation and delivery of these vaccines are considered.

Safety and immunogenicity of an MF59-adjuvanted subunit influenza vaccine in elderly Chinese subjects

BACKGROUND

The safety and immunogenicity of an MF59-adjuvanted subunit influenza vaccine (Sub/MF59; FLUAD, Novartis Vaccines) was evaluated among elderly Chinese subjects (> or = 60 years of age). After a preliminary Phase I, open-label study (n = 25) to assess safety 1-14 days post-vaccination, a comparative observer-blind, randomised, controlled clinical trial (n = 600) was performed to assess safety and immunogenicity versus a non-adjuvanted subunit influenza vaccine (Subunit; Agrippal, Novartis Vaccines). Subjects were randomised (2:1) to receive Sub/MF59 or Subunit.

RESULTS

Both vaccines were well tolerated, with no vaccine-related serious adverse events reported during the Phase I trial. During the observer-blind study, local and systemic reactions were generally similar for both vaccines 1-22 days post-vaccination; however, injection-site induration was more frequent among the Subunit group (P < 0.05), and mild pain at the injection site and fever were more frequent among Sub/MF59 recipients (P < or = 0.005). Both vaccines induced a significant (P < 0.001) increase in geometric mean titres (GMTs) for the three strains tested, versus baseline; GMTs against A/H1N1, A/H3N2 and B were significantly higher in the Sub/MF59 group (P = 0.034, P < 0.001 and P = 0.005, respectively). GMT ratios against A/H1N1, A/H3N2 and B were also significantly higher in the Sub/MF59 group (P = 0.038, P < 0.001 and P = 0.006, respectively). Similarly, the percentage of subjects achieving seroprotection or seroconversion on Day 22 was greater for Sub/MF59 recipients, reaching significance for A/H3N2 (P < 0.001).

CONCLUSION

MF59-adjuvanted subunit influenza vaccine is well tolerated by elderly Chinese subjects and induces a higher level of immunogenicity than a non-adjuvanted subunit influenza vaccine in this population that is at high risk of influenza-related complications.

CLINICAL TRIAL REGISTRY

http://www.clinicaltrials.gov, NCT00310648.

Cross-protection by MF59-adjuvanted influenza vaccine: neutralizing and haemagglutination-inhibiting antibody activity against A(H3N2) drifted influenza viruses

Adjuvants enhance antibody response against vaccination. We compared the ability of MF59-adjuvanted and non-adjuvanted subunit influenza vaccines, containing A/Wyoming/3/03(H3N2), to confer cross-protection against four consecutive drifted strains in the elderly. Neutralizing and haemagglutination-inhibiting antibody were measured. MF59-adjuvanted vaccine induced a stronger booster response against A/Panama/2007/99(H3N2) than non-adjuvanted vaccine. A/Panama/2007/99(H3N2) circulated widely during the previous 5 years and was included in vaccines over four consecutive seasons. Broader serological protection against drifted strains that circulated 1 and 2 years after vaccination with A/Wyoming/3/03(H3N2) was observed with MF59-adjuvanted vaccine. Thus, MF59-adjuvanted vaccine confers greater immunogenicity than non-adjuvanted vaccines in vulnerable populations.

Challenges for vaccination in the elderly

The increased susceptibility of the elderly to infection presents a major challenge to public health services. An aging immune system is well documented as the cause of increased infection rates in elderly people. Such immunosenescence is multi-factorial and incompletely understood. Immunosenescent changes include malfunctioning of innate immune system cellular receptors; involution of the thymus, with consequent reduction of the naïve T cell population; alteration of the T cell population composition; modified phenotypes of individual T cells; and replicative senescence of memory cells expressing naïve markers. Unfortunately, immunosenescence also renders vaccination less effective in the elderly. It is therefore important that the vaccines used against common but preventable diseases, such as influenza, are specifically enhanced to overcome the reduced immune responsiveness of this vulnerable population.

MF59-adjuvanted subunit influenza vaccine: an improved interpandemic influenza vaccine for vulnerable populations

Influenza is a highly contagious respiratory disease associated with substantial morbidity and mortality in vulnerable populations, especially the elderly. Influenza viruses are unique in that they undergo small mutations and antigenic variation in their hemagglutinin and neuraminidase genes. Owing to the senescence of the immune system, the ability to mount novel immune responses may be particularly compromised in older people. Fluad (Novartis Vaccines), an MF59-adjuvanted subunit influenza vaccine, was formulated in order to achieve greater immunogenicity in those groups who need a higher protection than that brought about by conventional vaccines. This article summarizes the main characteristics of MF59-adjuvanted subunit influenza vaccine, the clinical effectiveness data that have been generated in recent years and future developments.

MF59 is a safe and potent vaccine adjuvant for flu vaccines in humans: what did we learn during its development?

The MF59 adjuvant has been included in a licensed influenza vaccine for a decade. Hence, we have a significant amount of clinical data to establish its potency and safety. We can now reassess our early preclinical studies and determine whether or not they were useful to predict human responses. The main lesson learned is that mouse models can be valuable, but one must ask the right questions and the models must be used appropriately.

Effectiveness of MF59-adjuvanted subunit influenza vaccine in preventing hospitalisations for cardiovascular disease, cerebrovascular disease and pneumonia in the elderly

Annual circulation of influenza virus coincides with a peak in cardiovascular and pneumonia mortality/morbidity. This study aimed to determine the effectiveness of MF59-adjuvanted subunit influenza vaccine in preventing hospitalisation due to acute coronary syndrome (ACS), cerebrovascular accident (CVA) and pneumonia in the elderly. Three case-control studies were performed during the 2004-2005 influenza season in three health districts in Valencia, Spain (total elderly [>64 years of age] population: n=105,454). Controls were patients admitted for an acute surgical process or trauma within 10 days of case admission. In total, 159 patients were hospitalised for ACS, 148 for CVA and 242 for pneumonia. The risk of hospitalisation after the start of the influenza season was significantly lower in vaccinated patients compared with non-vaccinated patients (adjusted odds ratios: 0.13 [P=0.013] for ACS; 0.07 [P=0.007] for CVA; 0.31 [P=0.005] for pneumonia). During peak virus circulation, vaccination with MF59-adjuvanted subunit influenza vaccine was associated with an 87% relative risk reduction in hospitalisation for ACS, 93% for CVA, and 69% for pneumonia.

Response of Influenza Vaccines Against Heterovariant Influenza Virus Strains in Adults with Chronic Diseases

The ability of influenza vaccination to provide cross-protection against heterovariant influenza strains was evaluated in a double-blind, randomized, trial in north-east Italy during the winter of 2005-2006. Of 238 adult subjects with underlying chronic diseases, 120 received MF59-adjuvanted subunit vaccine (Sub/MF59) and 118 received a conventional subunit vaccine (Subunit). Immunogenicity was measured for A/H3N2 and B influenza strains against both the homologous vaccine strains (A/New York/55/2004 and B/Jiangsu/10/2003), and the heterovariant strains recommended for the 2006-2007 season (A/Wisconsin/67/2005 and B/Malaysia/2506/2004). Although both vaccines conferred serological protection against the homologous vaccine strains and the 2006-2007 heterovariant A/H3N2 strain for a majority of subjects, the antibody response was highest in the Sub/MF59 vaccine group. For example, MF59-adjuvanted vaccination conferred significantly greater (P = 0.002) protection against the heterovariant A/H3N2 strain than the conventional subunit vaccine (79.2% vs. 61.0% of subjects, respectively). In conclusion, these results demonstrate that protection provided by influenza vaccination in adults affected by chronic diseases is lower against heterovariant strains than for homologous strains. However, addition of MF59 adjuvant to a subunit vaccine enhances immunogenicity against the A/H3N2 heterovariant strain, conferring broader protection than a conventional subunit vaccine in this population, who are at higher risk of influenza-related complications.

Development of a mucosal vaccine for influenza viruses: preparation for a potential influenza pandemic

Highly pathogenic avian H5N1 influenza A virus has caused influenza outbreaks in poultry and migratory birds in Southeast Asia, Africa and Europe, and there is concern that it could cause a new pandemic. This fear of an emerging pandemic of a new influenza strain underscores the urgency of preparing effective vaccines to meet the pandemic. One way to mitigate current concerns is to develop an influenza vaccine that is fully functional against drift influenza viruses. In our current situation, in which we cannot predict which strain will cause a pandemic, cross-protective immunity using potential and novel mucosal vaccines plays a particularly important role in preventing the spread of highly pathogenic influenza virus.

MF59-adjuvanted influenza vaccine confers superior immunogenicity in adult subjects (18–60 years of age) with chronic diseases who are at risk of post-influenza complications

The immunogenicity and reactogenicity of two influenza vaccines were evaluated in a randomised, double-blind trial in north-east Italy during winter 2005-2006. Of 238 adult subjects (18-60 years of age) with underlying chronic diseases, 120 received MF59-adjuvanted subunit vaccine (Sub/MF59) and 118 received conventional subunit vaccine (Subunit). At 4 weeks post-vaccination, geometric mean titres (GMT) were significantly (P<0.001) increased for both groups. For the A/H3N2 and B strains, significantly (P<0.02) higher GMT were reported for the Sub/MF59 group. The mean-fold increase in titre, the percentage of subjects with at least a four-fold titre increase and the seroprotection rate (>or=1:40) were also higher in the Sub/MF59 group, with the seroprotection rate and four-fold titre increase achieving significance (P=0.002 and P=0.02, respectively) for the A/H3N2 strain. Our results suggest that adults affected by chronic diseases can mount a satisfactory immune response to influenza vaccines, and that these vaccines are well tolerated. Addition of the MF59-adjuvant, however, enhances the immunogenicity of subunit influenza vaccine, conferring superior protection than a conventional subunit vaccine in this population, who are at high-risk of influenza-related complications.

Preclinical evaluation of microneedle technology for intradermal delivery of influenza vaccines

Recent clinical studies have suggested that, for certain strains of influenza virus, intradermal (i.d.) delivery may enable protective immune responses using a lower dose of vaccine than required by intramuscular (i.m.) injection. Here, we describe the first preclinical use of microneedle technology for i.d. administration of three different types of influenza vaccines: (i) a whole inactivated influenza virus, (ii) a trivalent split-virion human vaccine, and (iii) a plasmid DNA encoding the influenza virus hemagglutinin. In a rat model, i.d. delivery of the whole inactivated virus provided up to 100-fold dose sparing compared to i.m. injection. In addition, i.d. delivery of the trivalent human vaccine enabled at least 10-fold dose sparing for the H1N1 strain and elicited levels of response across the dose range similar to those of i.m. injection for the H3N2 and B strains. Furthermore, at least fivefold dose sparing from i.d. delivery was evident in animals treated with multiple doses of DNA plasmid vaccine, although such effects were not apparent after the first immunization. Altogether, the results demonstrate that microneedle-based i.d. delivery elicits antibody responses that are at least as strong as via i.m. injection and that, in many cases, dose sparing can be achieved by this new immunization method.

Lack of effect of a booster dose of influenza vaccine in hemodialysis patients

To assess whether the administration of a booster dose of influenza vaccine may enhance immune response in hemodialysis patients, 58 subjects were given two doses of the 2003/2004 season influenza vaccine, 1 month apart. "European Agency for the Evaluation of Medicinal Products" (EMEA) criteria were fully met in terms of percentage of response and of mean-fold increase of hemagglutination inhibiting (HI) antibody titer, but not in terms of seroprotection rates (HI antibody titers > or =1:40). The second vaccine administration did not result in additional increase in seroprotection rate or in geometric mean titers. Protective immune response against the epidemic A/H3N2 Fujian-like strain, antigenically distant from that included in the vaccine (A/Panama/2007/99) was observed in 94.7% of vaccinees protected against the A/H3N2 vaccine strain 1 month after immunization. No adverse reactions were reported during follow-up. The study findings suggest that immune response to influenza vaccination may be suboptimal in hemodialysis patients and that the administration of an additional second dose of vaccine does not improve the humoral response.