A phase 1, open-label, randomized study to compare the immunogenicity and safety of different administration routes and doses of virosomal influenza vaccine in elderly.

BACKGROUND: Influenza remains a significant problem in elderly despite widespread vaccination coverage. This randomized, phase-I study in elderly compared different strategies of improving vaccine immunogenicity. METHODS: A total of 370 healthy participants (⩾65years) were randomized equally 1:1:1:1:1:1 to six influenza vaccine treatments (approximately 60-63 participants per treatment arm) at day 1 that consisted of three investigational virosomal vaccine formulations at doses of 7.5, 15, and 45µg HA antigen/strain administered intradermally (ID) by MicronJet600™ microneedle device (NanoPass Technologies) or intramuscularly (IM), and three comparator registered seasonal vaccines; Inflexal V™ (Janssen) and MF59 adjuvanted Fluad™ (Novartis) administered IM and Intanza™ (Sanofi Pasteur) administered ID via Soluvia™ prefilled microinjection system (BD). Serological evaluations were performed at days 22 and 90 and safety followed-up for 6months. RESULTS: Intradermal delivery of virosomal vaccine using MicronJet600™ resulted in significantly higher immunogenicity than the equivalent dose of virosomal Inflexal V™ administered intramuscularly across most of the parameters and strains, as well as in some of the readouts and strains as compared with the 45µg dose of virosomal vaccine formulation. Of 370 participants, 300 (81.1%) reported ⩾1 adverse event (AE); more participants reported solicited local AEs (72.2%) than solicited systemic AEs (12.2%). CONCLUSIONS: Intradermal delivery significantly improved influenza vaccine immunogenicity compared with intramuscular delivery. Triple dose (45µg) virosomal vaccine did not demonstrate any benefit on vaccine's immunogenicity over 15µg commercial presentation. All treatments were generally safe and well-tolerated.

Long-term Serologic Follow-up of Children Vaccinated with a Pediatric Formulation of Virosomal Hepatitis A Vaccine Administered With Routine Childhood Vaccines at 12-15 Months of Age.

BACKGROUND: The aim of this open-label, active-controlled, parallel group, phase 2 follow-up study was to assess the long-term immunogenicity of Epaxal Junior, the pediatric dose of an aluminum-free virosomal inactivated hepatitis A virus (HAV) vaccine, in children receiving routine childhood vaccines (RCV). METHODS: Healthy children (12-15 months old, ≥8 kg weight) were randomized (1:1:1) to group A: Epaxal Junior + RCV (day 1); group B: Epaxal Junior (day 1) + RCV (day 29) and group C: Havrix 720 + RCV (day 1). All 3 groups received 2 doses of HAV vaccines 6 months apart. Children who completed the primary study were followed up from 18 months to 7.5 years post booster. RESULTS: Of 291/327 randomized children who had completed the primary study, 157 were followed for the 7.5-year analysis (group A: 50; group B: 54; and group C: 53). Of these, 152 children had protective levels of anti-HAV antibodies [≥10 mIU/mL; 98% (group A); 96.3% (group B); 96.2% (group C)]. Anti-HAV geometric mean concentrations were similar in groups A and B at all the time points (1.5-, 2.5-, 3.5-, 5.25- and 7.5-year time point) but slightly lower in group C. Predictions of the median duration of persistence of seroprotective antibody levels, using the linear mixed model were similar in all groups: (group A: 19.1 years, group B: 18.7 years, group C: 17.3 years). CONCLUSIONS: Immunization with Epaxal Junior administered with RCVs at 12 months elicited protective response beyond 7.5 years in almost all children. Assessing the kinetic of anti-HAV antibody titers decline over time, the moment to reach antibody concentrations below the accepted protective level may occur earlier than previously estimated.

Establishment of a new quality control and vaccine safety test for influenza vaccines and adjuvants using gene expression profiling.

We have previously identified 17 biomarker genes which were upregulated by whole virion influenza vaccines, and reported that gene expression profiles of these biomarker genes had a good correlation with conventional animal safety tests checking body weight and leukocyte counts. In this study, we have shown that conventional animal tests showed varied and no dose-dependent results in serially diluted bulk materials of influenza HA vaccines. In contrast, dose dependency was clearly shown in the expression profiles of biomarker genes, demonstrating higher sensitivity of gene expression analysis than the current animal safety tests of influenza vaccines. The introduction of branched DNA based-concurrent expression analysis could simplify the complexity of multiple gene expression approach, and could shorten the test period from 7 days to 3 days. Furthermore, upregulation of 10 genes, Zbp1, Mx2, Irf7, Lgals9, Ifi47, Tapbp, Timp1, Trafd1, Psmb9, and Tap2, was seen upon virosomal-adjuvanted vaccine treatment, indicating that these biomarkers could be useful for the safety control of virosomal-adjuvanted vaccines. In summary, profiling biomarker gene expression could be a useful, rapid, and highly sensitive method of animal safety testing compared with conventional methods, and could be used to evaluate the safety of various types of influenza vaccines, including adjuvanted vaccine.

Acute disseminated encephalomyelitis with severe neurological outcomes following virosomal seasonal influenza vaccine.

Acute disseminated encephalomyelitis (ADEM) is an inflammatory, usually monophasic, immune mediate, demyelinating disease of the central nervous system which involves the white matter. ADEM is more frequent in children and usually occurs after viral infections, but may follow vaccinations, bacterial infections, or may occur without previous events. Only 5% of cases of ADEM are preceded by vaccination within one month prior to symptoms onset. The diagnosis of ADEM requires both multifocal involvement and encephalopathy and specific demyelinating lesions of white matter. Overall prognosis of ADEM patients is often favorable, with full recovery reported in 23% to 100% of patients from pediatric cohorts, and more severe outcome in adult patients. We describe the first case of ADEM occurred few days after administration of virosomal seasonal influenza vaccine. The patient, a 59-year-old caucasic man with unremarkable past medical history presented at admission decreased alertness, 10 days after flu vaccination. During the 2 days following hospitalization, his clinical conditions deteriorated with drowsiness and fever until coma. The magnetic resonance imaging of the brain showed multiple and symmetrical white matter lesions in both cerebellar and cerebral hemispheres, suggesting demyelinating disease with inflammatory activity, compatible with ADEM. The patient was treated with high dose of steroids and intravenous immunoglobulin with relevant sequelae and severe neurological outcomes.

Immunogenicity and safety of a pediatric dose of a virosomal hepatitis A vaccine in healthy children in India.

As India is transitioning from high to intermediate hepatitis A endemicity, the need for hepatitis A vaccination programs increases. This study investigated the immunogenicity and safety of a virosomal hepatitis A vaccine (HAVpur Junior) compared with an aluminum-adsorbed hepatitis A vaccine (Havrix 720 Junior) in Indian children. Healthy children aged 18-47 months, stratified by age, were randomized to either HAVpur Junior or Havrix 720 Junior. The first dose of vaccine was administered on Day 1 and the second (booster) dose 6 months later. Antibodies against hepatitis A virus (HAV) were measured using a microparticle enzyme immunoassay. The primary objective assessed non-inferiority of HAVpur Junior to Havrix 720 Junior in terms of seroprotection rates (≥ 10 mIU/mL anti-HAV antibodies) at 1 month after the first vaccination. Non-inferiority was demonstrated if the lower limit of the 90% confidence interval of the group difference was greater than -10%. Local and systemic adverse events were recorded. The seroprotection rate at 1 month was 95.9% in the HAVpur Junior group and 96.6% in the Havrix 720 Junior group. As the lower limit of the 90% confidence interval of the group difference was greater than -10% (-4.7), non-inferiority of HAVpur Junior to Havrix 720 Junior was established. The overall incidence of adverse events (solicited and unsolicited) after each vaccination was similar in both groups. In conclusion, the aluminum-free virosomal vaccine HAVpur Junior induced a similar immune response to Havrix 720 Junior in healthy Indian children aged 18 to 47 months. Both vaccines were well tolerated. The study shows that the low-dose virosomal HAV vaccine is consistently efficacious and well tolerated in children of all age groups and is suitable for inclusion into Indian childhood vaccination schedules.

Evaluation of an intranasal virosomal vaccine against respiratory syncytial virus in mice: effect of TLR2 and NOD2 ligands on induction of systemic and mucosal immune responses.

INTRODUCTION: RSV infection remains a serious threat to newborns and the elderly. Currently, there is no vaccine available to prevent RSV infection. A mucosal RSV vaccine would be attractive as it could induce mucosal as well as systemic antibodies, capable of protecting both the upper and lower respiratory tract. Previously, we reported on a virosomal RSV vaccine for intramuscular injection with intrinsic adjuvant properties mediated by an incorporated lipophilic Toll-like receptor 2 (TLR2) ligand. However, it has not been investigated whether this virosomal RSV vaccine candidate would be suitable for use in mucosal immunization strategies and if additional incorporation of other innate receptor ligands, like NOD2-ligand, could further enhance the immunogenicity and protective efficacy of the vaccine. OBJECTIVE: To explore if intranasal (IN) immunization with a virosomal RSV vaccine, supplemented with TLR2 and/or NOD2-ligands, is an effective strategy to induce RSV-specific immunity. METHODS: We produced RSV-virosomes carrying TLR2 (Pam3CSK4) and/or NOD2 (L18-MDP) ligands. We tested the immunopotentiating properties of these virosomes in vitro, using TLR2- and/or NOD2-ligand-responsive murine and human cell lines, and in vivo by assessing induction of protective antibody and cellular responses upon IN immunization of BALB/c mice. RESULTS: Incorporation of Pam3CSK4 and/or L18-MDP potentiates the capacity of virosomes to activate (antigen-presenting) cells in vitro, as demonstrated by NF-κB induction. In vivo, incorporation of Pam3CSK4 in virosomes boosted serum IgG antibody responses and mucosal antibody responses after IN immunization. While L18-MDP alone was ineffective, incorporation of L18-MDP in Pam3CSK4-carrying virosomes further boosted mucosal antibody responses. Finally, IN immunization with adjuvanted virosomes, particularly Pam3CSK4/L18-MDP-adjuvanted-virosomes, protected mice against infection with RSV, without priming for enhanced disease. CONCLUSION: Mucosal immunization with RSV-virosomes, supplemented with incorporated TLR2- and/or NOD2-ligands, represents a promising approach to induce effective and safe RSV-specific immunity.

A virosomal respiratory syncytial virus vaccine adjuvanted with monophosphoryl lipid A provides protection against viral challenge without priming for enhanced disease in cotton rats.

BACKGROUND: Non-replicating respiratory syncytial virus (RSV) vaccine candidates could potentially prime for enhanced respiratory disease (ERD) due to a T-cell-mediated immunopathology, following RSV infection. Vaccines with built-in immune response modifiers, such as Toll-like receptor (TLR) ligands, may avoid such aberrant imprinting of the immune system. METHODS: We developed reconstituted RSV envelopes (virosomes) with incorporated TLR4 ligand, monophosphoryl lipid A (RSV-MPLA virosomes). Immune responses and lung pathology after vaccination and challenge were investigated in ERD-prone cotton rats and compared with responses induced by live virus and formaldehyde-inactivated vaccine (FI-RSV), a known cause of ERD upon RSV challenge. RESULTS: Vaccination with RSV-MPLA virosomes induced higher levels of virus-neutralizing antibodies than FI-RSV or live virus infection and provided protection against infection. FI-RSV, but not RSV-MPLA virosomes, primed for increases in expression of Th2 cytokines IL-4, IL-5, IL-13, and Th1 cytokine IL-1b, 6 hour-5 days after infection. By contrast, RSV-MPLA virosomes induced IFN-γ transcripts to similar levels as induced by live virus. Animals vaccinated with FI-RSV, but not RSV-MPLA virosomes showed alveolitis, with prominent neutrophil influx and peribronchiolar and perivascular infiltrates. CONCLUSION: These results show that RSV-MPLA virosomes represent a safe and immunogenic vaccine candidate that warrants evaluation in a clinical setting.

Head-to-head comparison of an intradermal and a virosome influenza vaccine in patients over the age of 60: evaluation of immunogenicity, cross-protection, safety and tolerability.

In the present study we first compare immunogenicity against vaccine and heterologous circulating A(H1N1)pdm09 strains, tolerability and safety of intradermal Intanza 15 µg and of virosomal adjuvanted, intramuscularly delivered influenza vaccine, Inflexal V, in healthy elderly volunteers. Five-hundred participants were enrolled in the study and randomly assigned to the two vaccine groups to receive either one dose of Intanza 15 µg or Inflexal V vaccine. All subjects reported solicited local and systemic reactions occurred within 7 d after vaccination and unsolicited adverse events up to 21 d post-immunization and any serious adverse event appeared during the study. A subset of 55 participants was randomly selected for immunogenicity and cross-protection evaluations. Serum samples were collected before and 1 and 3 mo after immunization. Antibody responses were measured using hemagglutination inhibition (HI) against all viruses used in the study and neutralization (NT) assays against A(H1N1)pdm09 strains. At least one of the CHMP criteria for influenza vaccine approval in the elderly was met by virosomal vaccine against all the tested viruses; intradermal vaccine met all criteria against all strains. Several parameters of immune response against strains with a different antigenic pattern from that of vaccine A/California/04/09(H1N1)pdm09 were significantly higher in the intradermal vaccine group compared with the virosomal group. Safety and systemic tolerability of both vaccines were excellent, but injection site reactions occurred significantly more frequently in the intradermal vaccination group. Immunogenicity of Intanza 15 µg intradermal vaccine tended to be higher than that of Inflexal V against heterologous strains in healthy elderly.

Safety and immunogenicity of a Sf9 insect cell-derived respiratory syncytial virus fusion protein nanoparticle vaccine.

OBJECTIVE: We performed a Phase 1 randomized, observer-blinded, placebo-controlled trial to evaluate the safety and immunogenicity of a recombinant respiratory syncytial virus (RSV) fusion (F) protein nanoparticle vaccine. METHODS: Six formulations with (5, 15, 30 and 60 µg) and without (30 and 60 µg) aluminum phosphate (AdjuPhos) were administered intramuscularly on day 0 and 30 in a dose escalating fashion to healthy adults 18-49 years of age. Solicited and unsolicited events were collected through day 210. Immunogenicity measures taken at day 0, 30 and 60 included RSV A and B microneutralization, anti-F IgG, antigenic site II peptide and palivizumab competitive antibodies. RESULTS: The vaccine was well-tolerated, with no evident dose-related toxicity or attributable SAEs. At day 60 both RSV A and B microneutralization was significantly increased in vaccinees versus placebo. Across all vaccinees there was a 7- to 19-fold increase in the anti-F IgG and a 7- to 24-fold increase in the antigenic site II binding and palivizumab competitive antibodies. CONCLUSIONS: The RSV F nanoparticle vaccine candidate was well tolerated without dose-related increases in adverse events. Measures of immunity indicate that neutralization, anti-RSV F IgG titers and palivizumab competing antibodies were induced at levels that have been associated with decreased risk of hospitalization. NCT01290419.

The immunogenicity and safety of a single 0.5 mL dose of virosomal subunit influenza vaccine administered to unprimed children aged ≥6 to <36 months: data from a randomized, Phase III study.

This study evaluated the immunogenicity, safety and tolerability of a single 0.5 mL dose of the seasonal virosomal subunit influenza vaccine (Inflexal V, Crucell, Switzerland) in 205 healthy, unprimed children aged at least 6 to <36 months, evaluated at four weeks post-vaccination and seven months from baseline. Of the enrolled children, 102 received one single 0.5 mL dose and 103 received the standard two 0.25 mL doses given four weeks apart. Both treatments evoked an immune response that satisfied the EMA/CHMP criteria for yearly vaccine licensing for all three vaccine strains. Exploratory analyses revealed no differences between the groups at four weeks post-vaccination. Furthermore, immunogenicity was maintained seven months after the first vaccination after both the 0.5 mL and standard two 0.25 mL doses. Adverse events were comparable between groups and were as expected according to the safety profile of the vaccine; overall, the vaccine was well tolerated. Our results show that a single 0.5 mL dose effectively and safely provided long-term immunogenicity to all three influenza strains in unprimed children aged at least 6 to <36 months.

[Comparison of seasonal influenza vaccines: composition and properties]. / Saisonale Influenza-Impfstoffe: Zusammensetzung und Eigenschaften.

The influenza virus isolation in embryonated chicken eggs was possible early in 1930er years and allowed the influenza vaccine production. Most influenza vaccines were derived from this, but actually new virus cell culture methods are established. For better tolerability, influenza vaccines include only antigen proportions (split- and subunit vaccines) but with the disadvantage of minor vaccine efficacy. This was compared with the addition of adjuvants. Aluminium salts are used for many decades and still in use to enhance the effect of vaccines. New formulations are MF59, AS03, AS04 or toll- like receptor-agonists. Also virosomal formulations and "ISCOMs"(Immune Stimulating Complexes) are newly designed and compromises enhanced immune reactions. Actually a broad range of various influenza vaccines exist and are available for a very different group of patients (which depends on physical conditions, age, immune status or allergies).

Immunogenicity and tolerability of a paediatric presentation of a virosomal hepatitis A vaccine in Chilean children aged 1-16 years.

We assessed the immunogenicity of the paediatric dose of Epaxal(®) (0.25 mL) and the degrees of seroprotection achieved with the standard dose (0.5 mL) of Epaxal(®) or a dose of Havrix(®) Junior, in children in an open, randomised, controlled, multi-centre, parallel-group study conducted at 2 Chilean study centres. 360 healthy children and adolescents 12 months to <17 years of age not previously vaccinated against hepatitis A were enrolled. Subjects were randomised 2:2:1 to be vaccinated with either Epaxal(®) 0.25 mL [n=146], Epaxal(®) 0.5 mL [n=142] or Havrix(®) Junior [n=72] intramuscularly on Day 1 and after 6 months (26 weeks±14 days). Primary end point was the proportion of subjects seroprotected (anti-HAV antibody concentration ≥10 mIU/mL) in the ATP population at Month 1. All vaccines elicited high seroprotection rates at Month 1: 95.7% with Epaxal(®) 0.25 mL, 99.3% with Epaxal(®) 0.5 mL and 94.0% with Havrix(®) Junior. After the booster vaccination, all subjects demonstrated 100% seroprotection with all vaccines. Antibody concentrations were similarly high in all age groups. The paediatric presentation achieved antibody concentrations similar to those achieved with the 0.5 mL dose across the entire age range, and there were no differences across the range of body weights from 9.0 kg to 82.7 kg. All study vaccines were well tolerated and there were no AEs leading to discontinuation. Thus, the paediatric 0.25 mL dose of Epaxal(®) fulfilled the primary objective of showing non-inferiority to the adult 0.5 mL dose and to Havrix(®) Junior, in terms of seroprotection rates achieved. The results show the paediatric dose of Epaxal(®) to be an attractive option when conducting childhood-vaccination programmes.

Safety and immunogenicity of a virus-like particle pandemic influenza A (H1N1) 2009 vaccine in a blinded, randomized, placebo-controlled trial of adults in Mexico.

Virus-like particles (VLPs) can be rapidly developed from influenza virus genetic sequences in order to supply vaccine after the onset of a pandemic. The safety and immunogenicity of one or two doses of a recombinant A (H1N1) 2009 influenza VLP vaccine was evaluated in a two-stage, Phase 2, randomized, double-blind, placebo-controlled study conducted in 4563 healthy adults, 18-64 years of age, during the H1N1 2009 pandemic in Mexico. In Part A, 1013 subjects were randomized into four treatment groups (5 µg, 15 µg, or 45 µg hemagglutinin [HA] VLP vaccine or placebo) and vaccinated 21 days apart, with sera collected on Days 1, 14 and 36 for hemagglutination inhibition (HAI) testing. After review of safety and immunogenicity data from Part A, additional subjects were immunized with a single dose of 15 µg VLP vaccine (N=2537) or placebo (N=1011) and assessed for safety in Part B. Results showed the H1N1 2009 VLP vaccine was safe and well-tolerated. Systemic solicited events were similar between placebo and VLP vaccinated groups with no vaccine-related serious adverse events. Dose response trends for solicited local adverse events were observed, with higher incidences of local pain, swelling, tenderness, and redness reported in the higher VLP dose groups (15 µg and 45 µg) compared to the placebo and 5 µg VLP groups following both vaccinations. Although the majority of local AEs were mild in severity, a dose trend in events of moderate or greater severity was also noted for these solicited events. The VLP vaccine groups demonstrated robust HAI immune responses after a single vaccination, with high rates of seroprotection (≥ 40 HAI titer) in 82-92% of all subjects and in 64-85% of subjects who were seronegative at the time of immunization. HAI geometric mean titers (GMTs), geometric mean ratios (GMRs) and seroconversion rates were also all statistically higher in the VLP groups compared to placebo for both post-baseline time points. Based on these data, additional clinical trials are in development to evaluate influenza vaccine candidate antigens manufactured using Spodoptera frugiperda (Sf9)/baculovirus-based VLP technology.

Evaluation of a virosomal H5N1 vaccine formulated with Matrix M™ adjuvant in a phase I clinical trial.

The avian influenza H5 virus epizootic continues to cause zoonosis with human fatalities, highlighting the continued need for pandemic preparedness against this subtype. This study evaluated the tolerability and immunogenicity of a Matrix M™ adjuvanted virosomal H5N1 vaccine in a phase I clinical trial. Sixty healthy adults were vaccinated intramuscularly with two doses of influenza H5N1 (NIBRG-14) virosomal vaccine alone (30 µg haemagglutinin (HA)) or 1.5, 7.5 or 30 µg HA formulated with 50 µg Matrix M™ adjuvant. The antibody response was analysed by haemagglutination inhibition (HI), microneutralisation (MN) and single radial haemolysis (SRH) assays. The vaccine was well tolerated in all groups but injection site pain was more frequently observed in the Matrix M™ adjuvanted groups. The vaccine elicited homologous and heterologous H5N1-specific antibody responses and the Matrix M™ adjuvanted formulations met all the EU regulatory criteria. In conclusion, Matrix M™ adjuvant was well tolerated and augmented the antibody response allowing considerable dose sparing down to 1.5 µg HA.

Different influenza vaccine formulations and adjuvants for childhood influenza vaccination.

Pediatric influenza is a very common disease: attack rates range from 23% to 48% during interpandemic years and are significantly higher during pandemics. Influenza-related complications seem to be more common in children at risk because of an underlying chronic severe disease, but recently collected data clearly demonstrate that otherwise healthy children can also suffer from severe influenza and that the annual number of deaths is no different between the two groups. The aim of this review is to discuss the characteristics of all influenza vaccines in order to evaluate the real likelihood of prevention, as well as the safety and tolerability of the different formulations and adjuvants. The data indicate that further studies collecting efficacy and effectiveness data and evaluating the immunogenicity and safety of the different formulations and adjuvants should lead to the identification of more ideal influenza vaccines that could be used with significant advantage in the entire pediatric population.

Immunogenicity and safety of a pediatric dose virosomal hepatitis A vaccine in Thai HIV-infected children.

The immunogenicity and safety of a pediatric dose of a virosomal hepatitis A vaccine (Epaxal®) was evaluated in a group of 45 Thai children with human immunodeficiency virus (HIV) infection, age 2-16 years. Vaccines were administered at 0 and 6 months. Anti-HAV antibody titers were measured at baseline (before injection) 1 and 7 months after primary vaccination. The prevalence of HAV protective antibody in 45 Thai HIV-infected children was 13.6%. The seroprotection rate was 71% at 1 month and 100% at 7 months. The booster dose increased geometric mean concentration (GMC) from 106.5 mIU/ml to 3486.1 mIU/ml. Higher CD4 lymphocyte counts at enrollment was a predictive factor for HAV antibody response. Both doses of Epaxal® were well tolerated. These preliminary data suggest that a pediatric dose of Epaxal® is an effective hepatitis A vaccine for HIV-infected children and should be considered for implementation on a larger scale in the pediatric HIV population.

Pandemic influenza A/H1N1 vaccine administered sequentially or simultaneously with seasonal influenza vaccine to HIV-infected children and adolescents.

In order to evaluate the immunogenicity, safety and tolerability of the 2009 A/H1N1 MF59-adjuvanted influenza vaccine administered sequentially or simultaneously with seasonal virosomal-adjuvanted influenza vaccine to HIV-infected children and adolescents, 36 HIV-infected children and adolescents, and 36 age- and gender-matched healthy controls were randomised 1:1 to receive the pandemic vaccine upon enrollment and the seasonal vaccine one month later, or to receive the pandemic and seasonal vaccines simultaneously upon enrollment. Seroconversion and seroprotection rates against the pandemic influenza A/H1N1 virus were 100% two months after vaccine administration in both groups, regardless of the sequence of administration. Geometric mean titres against pandemic and seasonal antigens were significantly higher when the seasonal and pandemic vaccines were administered simultaneously than when the seasonal vaccine was administered alone. Local and systemic reactions were mild and not increased by simultaneous administration. In conclusion, the 2009 pandemic influenza A/H1N1 MF59-adjuvanted vaccine is as immunogenic, safe and well tolerated in HIV-infected children and adolescents as in healthy controls. Its simultaneous administration with virosomal-adjuvanted seasonal antigens seems to increase immune response to both pandemic and seasonal viruses with the same safety profile as that of the pandemic vaccine alone. However, because this finding cannot be clearly explained by an immunological viewpoint, further studies are needed to clarify the reasons of its occurrence.

A randomized clinical trial assessing immunogenicity and safety of a double dose of virosomal-adjuvanted influenza vaccine administered to unprimed children aged 6-35 months.

This study evaluated the immunogenicity of a double dose of the seasonal virosomal-adjuvanted influenza vaccine (Inflexal V, Crucell, The Netherlands) in 65 previously unvaccinated children aged less than 3 years: 43 received double doses (two doses of 0.50 mL 4 weeks apart) and 22 standard doses (two doses of 0.25 mL 4 weeks apart). Both treatments evoked a response that satisfied the EMEA criteria for adequate immunogenicity for all three vaccine strains, but the double dose had a significantly greater effect on all of the studied parameters of humoral and cell-mediated immune response (p<0.05). This result was achieved without any increase in the incidence of local and systemic adverse events. This means that doubling the dose of the virosomal-adjuvanted influenza vaccine (i.e. administering the same dose as that usually given to older children) effectively and safely increases the immune response to inactivated influenza vaccine in unprimed children aged less than 3 years.

Virus-like particles as particulate vaccines.

Particulate structures hold great promise for the development of effective and affordable recombinant prophylactic as well as therapeutic vaccines. Different types of particulate structures, including virus-like particles (VLPs) and virosomes, have been developed depending on the nature of the viral pathogen to be targeted and the type of immune response (humoral vs cellular) to be elicited. Particulate structures allow the insertion or fusion of foreign antigenic sequences, resulting in chimeric particles delivering foreign antigens on their surface. Similarly, they are used as carriers for foreign antigens, including non-protein antigens, via chemical conjugation. Particulate structures, indeed, represent a very efficient system for delivering antigens to antigen presenting cells (APC) which, in turn, trigger and amplify the adaptive immune response. The present review will address the biological and immunological properties of particulate structures, in particular VLPs, as platform for vaccine development.