Pharmacokinetics and tolerability of ABX464, a novel first-in-class compound to treat HIV infection, in healthy HIV-uninfected subjects

Background

An anti-HIV compound (ABX464) has been developed with a novel mechanism of activity in that it blocks viral gene expression in cells that are already infected.

Objectives

A first-in-man study was conducted to determine the pharmacokinetic and safety profiles of ABX464. This was carried out as an open label, parallel group, single ascending dose, exploratory study.

Methods

Twenty-four male subjects in good health without HIV infection, aged from 18 to 55 years old, with BMIs of 18-27 kg/m 2 were included. A single oral dose of ABX464 (50, 100, 150 or 200 mg) was administered on the morning of day 0 after overnight fasting, with follow-up for 45 days. Safety assessments consisted of vital signs, electrocardiogram, physical examination, laboratory tests and urinalysis. Pharmacokinetic parameters were calculated for ABX464 and its main metabolite ABX-464- N -glucuronide (ABX464-NGlc). The study was registered at https://www.clinicaltrials (trial number NCT02792686).

Results

ABX464 was well tolerated; the most frequent related treatment-emergent adverse events were headaches, nausea and vomiting; they were not considered as treatment-limiting effects. ABX464's C max was observed approximately 2 h after administration in all groups. ABX464 was rapidly and substantially metabolized into ABX464-NGlc. The C max of ABX464-NGlc was observed approximately 4 h post-dose and was about 160-fold higher than that of the parent with a much longer t 1/2 (90-110 h). The ratio of metabolite to parent drug was consistent across the complete dose range.

Conclusions

These studies confirmed that ABX464 is well tolerated and rapidly and substantially metabolized into ABX464-NGlc in human subjects.

Vero cell technology for rapid development of inactivated whole virus vaccines for emerging viral diseases

INTRODUCTION

Rapid development and production of vaccines against emerging diseases requires well established, validated, robust technologies to allow industrial scale production and accelerated licensure of products. Areas covered: A versatile Vero cell platform has been developed and utilized to deliver a wide range of candidate and licensed vaccines against emerging viral diseases. This platform builds on the 35 years' experience and safety record with inactivated whole virus vaccines such as polio vaccine. The current platform has been optimized to include a novel double inactivation procedure in order to ensure a highly robust inactivation procedure for novel emerging viruses. The utility of this platform in rapidly developing inactivated whole virus vaccines against pandemic (-like) influenza viruses and other emerging viruses such as West Nile, Chikungunya, Ross River and SARS is reviewed. The potential of the platform for development of vaccines against other emerging viruses such as Zika virus is described. Expert commentary: Use of this platform can substantially accelerate process development and facilitate licensure because of the substantial existing data set available for the cell matrix. However, programs to provide vaccines against emerging diseases must allow alternative clinical development paths to licensure, without the requirement to carry out large scale field efficacy studies.

Immunogenicity and protective efficacy of a Vero cell culture-derived whole-virus H7N9 vaccine in mice and guinea pigs

Background

A novel avian H7N9 virus with a high case fatality rate in humans emerged in China in 2013. We evaluated the immunogenicity and protective efficacy of a candidate Vero cell culture-derived whole-virus H7N9 vaccine in small animal models.

Methods

Antibody responses induced in immunized DBA/2J mice and guinea pigs were evaluated by hemagglutination inhibition (HI), microneutralization (MN), and neuraminidase inhibition (NAi) assays. T-helper cell responses and IgG subclass responses in mice were analyzed by ELISPOT and ELISA, respectively. Vaccine efficacy against lethal challenge with wild-type H7N9 virus was evaluated in immunized mice. H7N9-specific antibody responses induced in mice and guinea pigs were compared to those induced by a licensed whole-virus pandemic H1N1 (H1N1pdm09) vaccine.

Results

The whole-virus H7N9 vaccine induced dose-dependent H7N9-specific HI, MN and NAi antibodies in mice and guinea pigs. Evaluation of T-helper cell responses and IgG subclasses indicated the induction of a balanced Th1/Th2 response. Immunized mice were protected against lethal H7N9 challenge in a dose-dependent manner. H7N9 and H1N1pdm09 vaccines were similarly immunogenic.

Conclusions

The induction of H7N9-specific antibody and T cell responses and protection against lethal challenge suggest that the Vero cell culture-derived whole-virus vaccine would provide an effective intervention against the H7N9 virus.

Neuraminidase-Inhibiting Antibody Response to H5N1 Virus Vaccination in Chronically Ill and Immunocompromised Patients

Neuraminidase-inhibiting (NAi) antibodies have been reported to be an independent correlate of protection from influenza disease, but the NAi antibody response to influenza vaccination has never been assessed in chronically ill or immunocompromised participants. Using an enzyme-linked lectin assay, we demonstrated that 2 immunizations with a Vero cell culture-derived, whole-virus H5N1 A/Vietnam vaccine induces NAi antibodies in 94.3% of chronically ill and 83.8% of immunocompromised participants. A booster with a heterologous A/Indonesia H5N1 vaccine induced comparable NAi antibody titers in both groups and resulted in 100% seropositivity. These data support prepandemic H5N1 vaccination strategies for these highly vulnerable risk groups.

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

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

Hyperimmune intravenous immunoglobulin containing high titers of pandemic H1N1 hemagglutinin and neuraminidase antibodies provides dose-dependent protection against lethal virus challenge in SCID mice

Background

Convalescent plasma and fractionated immunoglobulins have been suggested as prophylactic or therapeutic interventions during an influenza pandemic.

Findings

Intravenous immunoglobulin (IVIG) preparations manufactured from human plasma collected before the 2009 H1N1 influenza pandemic, and post-pandemic hyperimmune (H)-IVIG preparations were characterized with respect to hemagglutination inhibition (HI), microneutralization (MN) and neuraminidase-inhibiting (NAi) antibody titers against pandemic H1N1 (pH1N1) and seasonal H1N1 (sH1N1) viruses. The protective efficacy of the IVIG and H-IVIG preparations was evaluated in a SCID mouse challenge model.

Substantial levels of HI, MN and NAi antibodies against pH1N1 (GMTs 1:45, 1:204 and 1: 727, respectively) and sH1N1 (GMTs 1:688, 1:4,946 and 1:312, respectively) were present in pre-pandemic IVIG preparations. In post-pandemic H-IVIG preparations, HI, MN and NAi antibody GMTs against pH1N1 were 1:1,280, 1:11,404 and 1:2,488 (28-, 56- and 3.4-fold enriched), respectively, compared to pre-pandemic IVIG preparations (p < 0.001). Post-pandemic H-IVIG (HI titer 1:1,280) provided complete protection from lethality of SCID mice against pH1N1 challenge (100% of mice survived for 29 days post-challenge). Pre-pandemic IVIG (HI titer 1:70) did not provide significant protection against pH1N1 challenge (50% of mice survived 29 days post-challenge compared to 40% survival in the buffer control group). There was a highly significant correlation between circulating in vivo HI and MN antibody titers and survival (p < 0001).

Conclusion

The substantial enrichment of HA- and NA-specific antibodies in H-IVIG and the efficacious protection of SCID mice against challenge with pH1N1 suggests H-IVIG as a promising intervention against pandemic influenza for immunocompromised patients and other risk groups.

Evaluation of OspA vaccination-induced serological correlates of protection against Lyme borreliosis in a mouse model

BACKGROUND

For clinical development of a novel multivalent OspA vaccine against Lyme borreliosis, serological assays are required which can be used to establish immune correlates of protection against infection with Borrelia.

METHODS

Four assays (an OspA IgG ELISA, a competitive inhibition (CI) ELISA, a Borrelia surface-binding (SB) assay and a Borrelia killing assay) were used to evaluate the correlation between immune responses induced by rOspA 1/2 (a chimeric immunogen containing protective epitopes from OspA serotypes 1 and 2), and protective immunity against infection by B. burgdorferi s.s. (OspA-1) and B. afzelii (OspA-2). Mice were immunized with OspA 1/2 doses ranging from 0.3 ng to 100 ng, to induce a range of OspA antibody titers, and exposed to needle challenge with B. burgdorferi s.s. or tick challenge with B. afzelii. Receiver operator characteristics (ROC) curves were constructed for each assay, and the area under the curve (AUC), sensitivity, specificity and Youden Index were calculated. Potential cutoff antibody titers which could be used as correlates of vaccine-induced protection were derived from the maximum Youden Index.

RESULTS

Immunization with OspA-1/2 provided dose-dependent protection against infection with B. burgdorferi s.s. and B. afzelii. Antibody responses detected by all four assays were highly significantly correlated with protection from infection by either B. burgdorferi s.s. (p<0.0001 to 0.0062) or B. afzelii (p<0.0001). ROC analyses of the diagnostic effectiveness of each assay showed the AUC to range between 0.95 and 0.79, demonstrating that all assays distinguish well between infected and non-infected animals. Based on sensitivity, specificity and AUC, the OspA IgG ELISA and SB assays best discriminated between infected and non-infected animals.

CONCLUSIONS

All four assays differentiate well between Borrelia-infected and non-infected animals. The relatively simple, high throughput IgG ELISA would be suitable to establish immune correlates of protection for the novel OspA vaccine in clinical trials.

Vero cell culture-derived pandemic influenza vaccines: preclinical and clinical development

Several subtypes of influenza A viruses with pandemic potential are endemic in bird populations throughout Asia, Africa and the Middle East, and evidence suggests that these viruses are adapting to the mammalian host. As emphasized by the high mortality rate of humans infected with H5N1 viruses, this situation presents a substantial risk to global human health. The Vero cell culture platform has been used to develop whole-virus influenza vaccines that provide broad cross-clade protection against viruses with pandemic potential, at low antigen doses, without the requirement for adjuvantation. The safety and immunogenicity of these vaccines has been demonstrated in studies with more than 10,000 individuals, including healthy adult and elderly subjects, children and various risk groups. These Vero cell-derived vaccines are licensed for prepandemic and pandemic use. The Vero platform is also being explored to develop next-generation live-attenuated and recombinant vaccines.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

CLINICAL TRIALS REGISTRATION

NCT01052402.

Quantitative detection of Borrelia burgdorferi sensu lato in erythema migrans skin lesions using internally controlled duplex real time PCR

B. burgdorferi sensu stricto, B. afzelii, B. garinii and B. bavariensis are the principal species which account for Lyme borreliosis (LB) globally. We have developed an internally controlled duplex quantitative real time PCR assay targeting the Borrelia 16S rRNA and the human RNAseP genes. This assay is well-suited for laboratory confirmation of suspected cases of LB and will be used to assess the efficacy of a vaccine against LB in clinical trials. The assay is highly specific, successfully detecting DNA extracted from 83 diverse B. burgdorferi sensu lato strains representing all major species causing LB, while 21 unrelated microbial species and human genomic DNA tested negative. The assay was highly reproducible and sensitive, with a lower limit of detection of 6 copies per PCR reaction. Together with culture, the assay was used to evaluate paired 3 mm skin biopsy samples taken from 121 patients presenting with solitary erythema migrans (EM) lesion. PCR testing identified more positive biopsy samples than culture (77.7% PCR positive versus 55.1% culture positive) and correctly identified all specimens scored as culture positive. OspA-based typing identified the majority of isolates as B. afzelii (96.8%) and the bacterial load was significantly higher in culture positive biopsies than in culture negative biopsies (P<0.001). The quantitative data also enabled relationships between Borrelia burden and patient symptoms to be evaluated. The bacterial load was significantly higher among patients with systemic symptoms than without (P = 0.02) and was significantly higher for biopsies retrieved from patients with EM lesions with central clearing (P<0.001). 16S copy numbers were moderately lower in samples from patients reporting a history of LB (P = 0.10). This is the first quantitative PCR study of human skin biopsies predominantly infected with B. afzelii and the first study to demonstrate a clear relationship between clinical symptoms in B. afzelii-infected patients and Borrelia burden.

Preclinical evaluation of Vaxfectin-adjuvanted Vero cell-derived seasonal split and pandemic whole virus influenza vaccines

Increasing the potency and supply of seasonal and pandemic influenza vaccines remains an important unmet medical need which may be effectively accomplished with adjuvanted egg- or cell culture-derived vaccines. Vaxfectin, a cationic lipid-based adjuvant with a favorable safety profile in phase 1 plasmid DNA vaccines trials, was tested in combination with seasonal split, trivalent and pandemic whole virus, monovalent influenza vaccines produced in Vero cell cultures. Comparison of hemagglutination inhibition (HI) antibody titers in Vaxfectin-adjuvanted to nonadjuvanted vaccinated mice and guinea pigs revealed 3- to 20-fold increases in antibody titers against each of the trivalent influenza virus vaccine strains and 2- to 8-fold increases in antibody titers against the monovalent H5N1 influenza virus vaccine strain. With the vaccine doses tested, comparable antibody responses were induced with formulations that were freshly prepared or refrigerated at conventional 2-8°C storage conditions for up to 6 mo. Comparison of T-cell frequencies measured by interferon-gamma ELISPOT assay between groups revealed increases of between 2- to 10-fold for each of the adjuvanted trivalent strains and up to 22-fold higher with monovalent H5N1 strain. Both trivalent and monovalent vaccines were easy to formulate with Vaxfectin by simple mixing. These preclinical data support further testing of Vaxfectin-adjuvanted Vero cell culture vaccines toward clinical studies designed to assess safety and immunogenicity of these vaccines in humans.

Cell culture (Vero cell) derived whole-virus non-adjuvanted H5N1 influenza vaccine induces long-lasting cross-reactive memory immune response: homologous or heterologous booster response following two dose or single dose priming

BACKGROUND

Influenza pandemic preparedness involves priming of the population with pre-pandemic vaccines. Such vaccines should be well tolerated and induce a long-lasting immunological memory that can effectively be boosted with a single dose of pandemic vaccine once available. The presented studies assessed different prime-boost regimens with a Vero cell-derived whole virus non-adjuvanted H5N1 vaccine.

METHODS

In one study, 281 healthy adult (18-59 years) and 280 elderly (≥ 60 years) subjects received two vaccinations, 21 days apart, with Vero cell-derived whole virus non-adjuvanted H5N1 vaccine (7.5 μg HA Antigen A/Vietnam/1203/2004) followed by a 6, 12-15, or 24 month booster (7.5 or 3.75μg A/Indonesia/05/2005 or A/Vietnam/1203/2004). In the other study, 230 healthy adults (18-59 years) received single dose priming (7.5 μg A/Vietnam/1203/2004) followed by a 12 month booster (7.5 or 3.75 μg A/Indonesia/05/2005). Antibody responses were assessed by microneutralization (MN) and single radial hemolysis (SRH) assay. Vaccine safety was assessed throughout.

RESULTS

Two dose priming was equally immunogenic in adults and the elderly: >72% of subjects in each population achieved MN titers ≥ 1:20 after the second vaccination. Booster vaccinations at 6, 12-15, and 24 months induced substantial antibody increases to both strains: after a 7.5 μg A/Indonesia/05/2005 booster, 93-95% of adults and 72-84% of the elderly achieved MN titers ≥ 1:20 against this strain. Homologous and heterologous booster responses were higher in the 7.5μg dose group than in the 3.75 μg dose group. Booster responses following single dose priming were similar; a 7.5 μg booster dose induced homologous MN titers ≥ 1:20 in 93% of subjects.

CONCLUSIONS

A Vero cell derived whole virus non-adjuvanted H5N1 influenza vaccine is well tolerated and induces long-lasting cross-clade immunological memory that can be effectively boosted 1-2 years after two dose or single dose priming, supporting its suitability for pre-pandemic vaccination.

A cell culture-derived whole-virus H5N1 vaccine induces long-lasting cross-clade protective immunity in mice which is augmented by a homologous or heterologous booster vaccination

BACKGROUND

Preparation for an H5N1 influenza pandemic in humans could include priming the population in the pre-pandemic period with a vaccine produced from an existing H5N1 vaccine strain, with the possibility of boosting with a pandemic virus vaccine when it becomes available. We investigated the longevity of the immune response after one or two priming immunizations with a whole-virus H5N1 vaccine and the extent to which this can be boosted by later immunization with either a homologous or heterologous vaccine.

METHODS

Mice received one or two priming immunizations with a Vero cell culture-derived, whole-virus clade 1 H5N1 vaccine formulated to contain either 750 ng or 30 ng hemagglutinin. Six months after the first priming immunization, mice received either a booster immunization with the same clade 1 vaccine or a heterologous clade 2.1 vaccine, or buffer. Humoral and cellular immune responses were evaluated before and at regular intervals after immunizations. Three weeks after booster immunization, mice were challenged with a lethal dose of wild-type H5N1 virus from clades 1, 2.1 or 2.2 and survival was monitored for 14 days.

RESULTS

One or two priming immunizations with the 750 ng or 30 ng HA formulations, respectively, induced H5N1-neutralizing antibody titers which were maintained for ≥ 6 months and provided long-term cross-clade protection against wild-type virus challenge. Both humoral and cellular immune responses were substantially increased by a booster immunization after 6 months. The broadest protective immunity was provided by an immunization regimen consisting of one or two priming immunizations with a clade 1 vaccine and a boosting immunization with a clade 2.1 vaccine.

CONCLUSIONS

These data support the concept that pre-pandemic vaccination can provide robust and long-lasting H5N1 immunity which could be effectively boosted by immunization either with another pre-pandemic vaccine or with the pandemic strain vaccine.

Antibody persistence after two vaccinations with either FSME-IMMUN® Junior or ENCEPUR® Children followed by third vaccination with FSME-IMMUN® Junior

Tick-borne encephalitis (TBE) vaccination strategies to induce optimal seroprotection in children are under constant evaluation. This multi-center, randomized, controlled, phase III clinical study examined antibody persistence in children aged 1-11 y following two prospectively administered doses of either the FSME-IMMUN® Junior or Encepur Children® vaccines, as well as investigating the immunogenicity, safety and vaccine interchangeability of a third vaccination with FSME-IMMUN(®) Junior. A high level of antibody persistence was observed in all subjects 6 mo after the first of two vaccinations with either pediatric TBE vaccine. Based on both immunological tests and viral antigens used, slightly higher seropositivity rates and higher GMCs /GMTs were found in children vaccinated with FSME-IMMUN® Junior compared with those who received Encepur® Children. Seropositivity rates across all age strata combined six months after the first vaccination with FSME-IMMUN® 0.25 mL Junior were 95.1% as determined by Immunozym ELISA, 93.2% as determined by Enzygnost ELISA and 95.3% as determined by NT; compared with 62.6%, 80.5% and 91.0% respectively after vaccination with Encepur® Children. A third vaccination with FSME-IMMUN(®) Junior induced 100% seropositivity in both study groups and was well tolerated as demonstrated by the low rates of systemic and injection site reactions. Subjects who received either FSME-IMMUN Junior® or Encepur(®) Children vaccine for the first two vaccinations and FSME-IMMUN Junior® for the third showed a comparably strong immune response regardless of the previous TBE vaccine administered, demonstrating that two vaccinations with Encepur® Children can successfully be followed by a third vaccination with FSME-IMMUN Junior®.

Pre-vaccination immunity and immune responses to a cell culture-derived whole-virus H1N1 vaccine are similar to a seasonal influenza vaccine

BACKGROUND

Immune responses to novel pandemic influenza vaccines may be influenced by previous exposure to antigenically similar seasonal strains.

METHODS

An open-label, randomized, phase I/II study was conducted to assess the immunogenicity and safety of a non-adjuvanted, inactivated whole-virus H1N1 A/California/07/2009 vaccine. 408 subjects were stratified by age (18-59 and >60 years) and randomized 1:1 to receive two vaccinations with either 3.75 or 7.5 μg hemagglutinin antigen 21 days apart. Safety, immunogenicity and the influence of seasonal influenza vaccination and antibody cross-reactivity with a seasonal H1N1 strain was assessed.

RESULTS

A single vaccination with either dose induced substantial increases in H1N1 A/California/07/2009 hemagglutination inhibition (HI) and neutralizing (MN) antibody titers in both adult and elderly subjects. A single 7.5 μg dose induced seroprotection rates of 86.9% in adults and 75.2% in elderly subjects. Two 7.5 μg vaccinations induced seroprotection rates in adult and elderly subjects of 90.9% and 89.1%, respectively. The robust immune response to vaccination was confirmed by analyses of neutralizing antibody titers. Both HI and MN antibodies persisted for ≥ 6 months post-vaccination. Between 34% and 49% of subjects had seroprotective levels of H1N1 A/California/07/2009 antibodies at baseline. Higher baseline HI titers were associated with receipt of the 2008-09 or 2009-10 seasonal influenza vaccine. High baseline A/California/07/2009 neutralizing antibody titers were also associated with high baseline titers against A/New Caledonia/20/99, a seasonal H1N1 strain which circulated and was included in the seasonal vaccine from 2000-01 to 2006-07. Pre-adsorption with A/H1N1/New Caledonia/20/99 antigen reduced A/H1N1/California/07/2009 baseline titers in 55% of tested sera. The vaccine was well tolerated with low rates of fever.

CONCLUSIONS

A whole-virus H1N1 A/California/07/2009 vaccine was safe and well tolerated and a single dose induced substantial immune responses similar to seasonal influenza vaccines, probably due to immunological priming by previous seasonal influenza vaccines or infections.

Chikungunya virus and the safety of plasma products

BACKGROUND

Chikungunya virus (CHIKV) outbreaks were previously restricted to parts of Africa, Indian Ocean Islands, South Asia, and Southeast Asia. In 2007, however, the first autochthonous CHIKV transmission was reported in Europe. High-level viremia, a mosquito vector that is also present in large urban areas of Europe and America, and uncertainty around the resistance of this Alphavirus toward physiochemical inactivation processes raised concerns about the safety of plasma derivatives. To verify the safety margins of plasma products with respect to CHIKV, commonly used virus inactivation steps were investigated for their effectiveness to inactivate this newly emerging virus.

STUDY DESIGN AND METHODS

Pasteurization for human serum albumin (HSA), vapor heating for Factor VIII inhibitor bypassing activity, solvent/detergent (S/D) treatment for intravenous immunoglobulin (IVIG), and incubation at low pH for IVIG were investigated for their capacity to inactivate CHIKV and the closely related Sindbis virus (SINV). The obtained results were compared to previous studies with West Nile virus and the commonly used model virus bovine viral diarrhea virus.

RESULTS

The data generated demonstrate the effective inactivation of CHIKV as well as SINV by the inactivation steps investigated and thereby support results from earlier validation studies in which model viruses were used.

CONCLUSION

High inactivation capacities with respect to CHIKV were demonstrated. This provides solid reassurance for the safety of plasma products and the results verify that the use of model viruses is appropriate to predict the inactivation characteristics of newly emerging viruses when their physicochemical properties are well characterized.

A cell culture-derived influenza vaccine provides consistent protection against infection and reduces the duration and severity of disease in infected individuals

A Vero cell culture–derived seasonal influenza vaccine provides consistently high levels of protection against cell culture–confirmed infection over a complete influenza season. Influenza symptoms are also less severe and of shorter duration in individuals who become infected despite vaccination.

Background. Current knowledge of the consistency of protection induced by seasonal influenza vaccines over the duration of a full influenza season is limited, and little is known about the clinical course of disease in individuals who become infected despite vaccination.

Methods. Data from a randomized double-blind placebo-controlled clinical trial undertaken in healthy young adults in the 2008–2009 influenza season were used to investigate the weekly cumulative efficacy of a Vero cell culture–derived influenza vaccine. In addition, the duration and severity of disease in vaccine and placebo recipients with cell culture–confirmed influenza infection were compared.

Results. Vaccine efficacy against matching strains was consistently high (73%–82%) throughout the study, including the entire period of the influenza season during which influenza activity was above the epidemic threshold. Vaccine efficacy was also consistent (68%–83%) when calculated for all strains, irrespective of antigenic match. Vaccination also ameliorated disease symptoms when infection was not prevented. Bivariate analysis of duration and severity showed a significant amelioration of myalgia (P = .003), headache (P = .025), and fatigue (P = .013) in infected vaccinated subjects compared with placebo. Cough (P = .143) and oropharyngeal pain (P = .083) were also reduced in infected vaccinated subjects.

Conclusions. A Vero cell culture–derived influenza vaccine provides consistently high levels of protection against cell culture–confirmed infection by seasonal influenza virus and significantly reduces the duration and severity of disease in those individuals in which infection is not prevented.

Clinical Trials Registration. ClinicalTrials.gov NCT00566345.

Quantitative comparison of the cross-protection induced by tick-borne encephalitis virus vaccines based on European and Far Eastern virus subtypes

Tick-borne encephalitis virus (TBEV) is a flavivirus of wide geographic distribution and the causative agent of tick-borne encephalitis (TBE), an infection of the central nervous system. TBE has the highest incidence rate in Russia, where locally produced as well as Western European vaccines for the prevention of TBE are available. The Western European vaccines are based on TBE viruses that belong to the European subtype, while the Russian vaccines are based on Far Eastern subtype viruses. The question of to which extent vaccination with a vaccine based on the European subtype is effective in protecting against the heterologous Far Eastern virus subtype - and vice versa - has not been answered conclusively. Here we immunized mice with TBE vaccines based on European and Far Eastern subtype viruses, and used an unbiased hybrid virus test system to determine cross-neutralizing antibody titers and cross-protective efficacy. All vaccines tested elicited cross-protective responses against the heterologous strains, similar to those induced against the respective homologous vaccine strains. These data, therefore, fully support the use of TBE vaccines in geographic regions where virus subtypes heterologous to the vaccine strains are prevalent.

Clinical development of a Vero cell culture-derived seasonal influenza vaccine

BACKGROUND

Cell culture technologies have the potential to improve the robustness and flexibility of influenza vaccine supply and to substantially shorten manufacturing timelines. We investigated the safety, immunogenicity and efficacy of a Vero cell culture-derived seasonal influenza vaccine and utilized these studies to establish a serological correlate of vaccine protection.

METHODS

Two multicenter, randomized, double-blind phase III trials were undertaken in the US during the 2008-2009 Northern hemisphere influenza season, in young (18-49 years) and older (50-64 years and ≥ 65 years) adult subjects. 7250 young adults were randomized 1:1 to receive either Vero-derived vaccine or placebo. 3210 older adult subjects were randomized 8:1 to receive either Vero-derived vaccine or a licensed egg-derived vaccine. Serum hemagglutination inhibition antibody titers were assessed 21 days post-vaccination. Vaccine efficacy in preventing cell culture-confirmed influenza infection was determined for the young adult population. Local and systemic adverse events were recorded in both studies.

RESULTS

The Vero-derived vaccine was safe and well tolerated in both young and older adults. All US and European immunological licensing thresholds were comfortably met in both populations. Vaccine efficacy in young adults was 79% against A/H1N1 viruses antigenically matching the corresponding vaccine strain and 78.5% for all antigenically matched influenza viruses. A hemagglutination inhibition antibody titer of ≥ 1:15 provided a reliable correlate of protection for the Vero-derived influenza vaccine, with no additional benefit at titers >1:30. Bridging of the correlate of protection established in the young adult population to the older adult immunogenicity data demonstrated the likely effectiveness of the Vero-derived vaccine in the older adult population.

CONCLUSIONS

A Vero cell culture-derived seasonal influenza vaccine is safe, immunogenic and protects against infection with influenza virus. The novel vaccine technology has the potential to make a substantial contribution to improving influenza vaccine supply.

CLINICAL TRIAL REGISTRATION

The studies are registered with ClinicalTrials.gov, numbers NCT00566345 and NCT00782431.

Safety and immunogenicity of an inactivated whole virus Vero cell-derived Ross River virus vaccine: a randomized trial

BACKGROUND

Ross River virus (RRV) is endemic in Australia and several South Pacific Islands. Approximately 5000 cases of RRV disease, which is characterized by debilitating polyarthritis, are recorded each year in Australia. This study describes the first clinical trial of a candidate RRV vaccine.

METHODS

An inactivated whole-virus Vero cell-derived RRV vaccine was tested in 382 healthy, RRV-naïve adults in a phase 1/2 dose-escalation study at ten sites in Austria, Belgium and The Netherlands. Subjects were equally randomized to receive 1.25 μg, 2.5 μg, 5 μg, or 10 μg aluminum hydroxide-adjuvanted or non-adjuvanted RRV vaccine, with a second dose after three weeks and a booster at six months. Vaccine immunogenicity was determined by measurements of serum IgG and neutralizing antibody titers. Vaccine tolerability and safety were monitored over the entire study period.

RESULTS

The optimal vaccine formulation was the adjuvanted 2.5 μg dose, as calculated using a repeated mixed model analysis of covariance comparing log-transformed RRV-specific IgG titers between different dose groups. Geometric means of RRV-specific serum antibodies measured 21 days after the third vaccination with the 2.5 μg adjuvanted formulation were 520.9 (90% CI 377.2-719.4) as determined by IgG ELISA and 119.9 (82.6-173.9) as determined by virus neutralization assay, resulting in seropositivity rates of 92.9% (82.6-98.0) and 92.7% (82.2-98.0), respectively. All vaccine formulations and doses were well tolerated after the first, second and third vaccination.

CONCLUSIONS

The adjuvanted, inactivated whole-virus Vero cell-derived Ross River virus vaccine is highly immunogenic in RRV-naïve adults and well tolerated at all dose levels.

Preparation of commercial quantities of a hyperimmune human intravenous immunoglobulin preparation against an emerging infectious disease: the example of pandemic H1N1 influenza

BACKGROUND

The recent H1N1 pandemic provided an opportunity to conceptually assess the possibility of rapidly providing a "hyperimmune" human immunoglobulin (H-IVIG) to an emerging infectious disease, in useful quantities with respect to public health. Commercial-scale H-IVIG production from plasma collected from donors convalescent from or vaccinated against pandemic influenza A (H1N1) virus is described.

STUDY DESIGN AND METHODS

A special protocol was implemented for the collection, processing, and shipment of plasma from previously qualified source plasma donors, self-identifying as convalescent from or vaccinated against H1N1 influenza. A licensed IVIG manufacturing process was utilized for the preparation of two commercial lots of approximately 50 kg 10% human IVIG preparation in total. The H1N1 hemagglutination inhibition and neutralization antibody titers of the resulting H-IVIG preparations were determined and compared with standard preparations.

RESULTS

Twenty-six plasma collection centers participated in the protocol. Donor enrollment exceeded 300 donors per week and within 30 days of protocol deployment plasma was being collected at a rate of more than 2000 L/week. Manufacture of both H-IVIG lots was unremarkable and both lots met the requirements for commercial release and the bulk of the product was distributed in normal commercial channels. Examination of plasma pools and final IVIG product confirmed pandemic H1N1 antibody titers substantially higher than those collected before the emergence of the pandemic H1N1 virus.

CONCLUSIONS

This work demonstrates the feasibility of producing a H-IVIG preparation at large scale relatively rapidly, with a significant enrichment in antibodies to the H1N1 influenza, achieved by donor self-identification.

H5N1 whole-virus vaccine induces neutralizing antibodies in humans which are protective in a mouse passive transfer model

Background

Vero cell culture-derived whole-virus H5N1 vaccines have been extensively tested in clinical trials and consistently demonstrated to be safe and immunogenic; however, clinical efficacy is difficult to evaluate in the absence of wide-spread human disease. A lethal mouse model has been utilized which allows investigation of the protective efficacy of active vaccination or passive transfer of vaccine induced sera following lethal H5N1 challenge.

Methods

We used passive transfer of immune sera to investigate antibody-mediated protection elicited by a Vero cell-derived, non-adjuvanted inactivated whole-virus H5N1 vaccine. Mice were injected intravenously with H5N1 vaccine-induced rodent or human immune sera and subsequently challenged with a lethal dose of wild-type H5N1 virus.

Results

Passive transfer of H5N1 vaccine-induced mouse, guinea pig and human immune sera provided dose-dependent protection of recipient mice against lethal challenge with wild-type H5N1 virus. Protective dose fifty values for serum H5N1 neutralizing antibody titers were calculated to be ≤1∶11 for all immune sera, independently of source species.

Conclusions

These data underpin the confidence that the Vero cell culture-derived, whole-virus H5N1 vaccine will be effective in a pandemic situation and support the use of neutralizing serum antibody titers as a correlate of protection for H5N1 vaccines.

Evaluation of an inactivated Ross River virus vaccine in active and passive mouse immunization models and establishment of a correlate of protection

Ross River Virus has caused reported outbreaks of epidemic polyarthritis, a chronic debilitating disease associated with significant long-term morbidity in Australia and the Pacific region since the 1920s. To address this public health concern, a formalin- and UV-inactivated whole virus vaccine grown in animal protein-free cell culture was developed and tested in preclinical studies to evaluate immunogenicity and efficacy in animal models. After active immunizations, the vaccine dose-dependently induced antibodies and protected adult mice from viremia and interferon α/β receptor knock-out (IFN-α/βR(-/-)) mice from death and disease. In passive transfer studies, administration of human vaccinee sera followed by RRV challenge protected adult mice from viremia and young mice from development of arthritic signs similar to human RRV-induced disease. Based on the good correlation between antibody titers in human sera and protection of animals, a correlate of protection was defined. This is of particular importance for the evaluation of the vaccine because of the comparatively low annual incidence of RRV disease, which renders a classical efficacy trial impractical. Antibody-dependent enhancement of infection, did not occur in mice even at low to undetectable concentrations of vaccine-induced antibodies. Also, RRV vaccine-induced antibodies were partially cross-protective against infection with a related alphavirus, Chikungunya virus, and did not enhance infection. Based on these findings, the inactivated RRV vaccine is expected to be efficacious and protect humans from RRV disease.

A new approach to a Lyme disease vaccine

A single recombinant outer surface protein A (OspA) antigen designed to contain protective elements from 2 different OspA serotypes (1 and 2) is able to induce antibody responses that protect mice against infection with either Borrelia burgdorferi sensu stricto (OspA serotype-1) or Borrelia afzelii (OspA serotype-2). Protection against infection with B burgdorferi ss strain ZS7 was demonstrated in a needle-challenge model. Protection against B. afzelii species was shown in a tick-challenge model using feral ticks. In both models, as little as .03 μg of antigen, when administered in a 2-dose immunization schedule with aluminum hydroxide as adjuvant, was sufficient to provide complete protection against the species targeted. This proof of principle study proves that knowledge of protective epitopes can be used for the rational design of effective, genetically modified vaccines requiring fewer OspA antigens and suggests that this approach may facilitate the development of an OspA vaccine for global use.

Increasing West Nile virus antibody titres in central European plasma donors from 2006 to 2010

We analysed by neutralisation assay 55 intravenous immunoglobulin preparations produced from human plasma collected in three central European countries, specifically Austria, Germany and the Czech Republic, from 2006 to 2010. The preparations from 2009 and 2010 contained increasing titres of neutralising antibodies against West Nile virus (WNV) in the absence of reported human WNV cases in these countries.

Efficacy, safety, and immunogenicity of a Vero-cell-culture-derived trivalent influenza vaccine: a multicentre, double-blind, randomised, placebo-controlled trial

BACKGROUND

The use of cell-culture technologies for the manufacture of influenza vaccines might contribute to improved strain selection and robust vaccine supplies. We investigated the safety, immunogenicity, and protective efficacy of a Vero-cell-culture-derived influenza vaccine, and assessed the correlation between vaccine efficacy and haemagglutination inhibition antibody titre.

METHODS

In a double-blind, placebo-controlled, phase 3 trial undertaken in 36 centres in the USA, healthy adults (aged 18-49 years) were randomly assigned in a 1:1 ratio to one injection of either placebo or Vero-cell-culture-derived influenza vaccine during the 2008-09 season. Randomisation was done in blocks by use of the random number generator algorithm, and participants were allocated by use of a centralised telephone system. The primary objective was the efficacy of the vaccine in preventing cell-culture-confirmed influenza infection with viruses that were antigenically matched to one of the vaccine strains. Analysis was by intention to treat. The study is registered with ClinicalTrials.gov, number NCT00566345.

FINDINGS

7250 participants were randomly assigned to vaccine (n=3626) and placebo (n=3624). 7236 were analysed for the primary outcome (n=3619 and n=3617, respectively). Overall protective efficacy for antigenically matched influenza infection was 78·5% (95% CI 60·8-88·2). The vaccine was well tolerated with no treatment-related serious adverse events. Adverse events were mainly mild and transient. An HI titre of at least 1:15 provided a reliable correlate of cell-culture-derived influenza vaccine-induced protection; no additional benefit was noted with titres greater than 1:30.

INTERPRETATION

The data indicate that existing correlates of protection afforded with egg-derived seasonal influenza vaccines also apply to this vaccine.

FUNDING

Federal (US Government) funds from the Office for Preparedness and Response, Biomedical Advanced Research and Development Authority, under contract to DynPort Vaccine Company.

Vectors based on modified vaccinia Ankara expressing influenza H5N1 hemagglutinin induce substantial cross-clade protective immunity

BACKGROUND

New highly pathogenic H5N1 influenza viruses are continuing to evolve with a potential threat for an influenza pandemic. So far, the H5N1 influenza viruses have not widely circulated in humans and therefore constitute a high risk for the non immune population. The aim of this study was to evaluate the cross-protective potential of the hemagglutinins of five H5N1 strains of divergent clades using a live attenuated modified vaccinia Ankara (MVA) vector vaccine.

METHODOLOGY/PRINCIPAL FINDINGS

The replication-deficient MVA virus was used to express influenza hemagglutinin (HA) proteins. Specifically, recombinant MVA viruses expressing the HA genes of the clade 1 virus A/Vietnam/1203/2004 (VN/1203), the clade 2.1.3 virus A/Indonesia/5/2005 (IN5/05), the clade 2.2 viruses A/turkey/Turkey/1/2005 (TT01/05) and A/chicken/Egypt/3/2006 (CE/06), and the clade 2.3.4 virus A/Anhui/1/2005 (AH1/05) were constructed. These experimental live vaccines were assessed in a lethal mouse model. Mice vaccinated with the VN/1203 hemagglutinin-expressing MVA induced excellent protection against all the above mentioned clades. Also mice vaccinated with the IN5/05 HA expressing MVA induced substantial protection against homologous and heterologous AH1/05 challenge. After vaccination with the CE/06 HA expressing MVA, mice were fully protected against clade 2.2 challenge and partially protected against challenge of other clades. Mice vaccinated with AH1/05 HA expressing MVA vectors were only partially protected against homologous and heterologous challenge. The live vaccines induced substantial amounts of neutralizing antibodies, mainly directed against the homologous challenge virus, and high levels of HA-specific IFN-γ secreting CD4 and CD8 T-cells against epitopes conserved among the H5 clades and subclades.

CONCLUSIONS/SIGNIFICANCE

The highest level of cross-protection was induced by the HA derived from the VN/1203 strain, suggesting that pandemic H5 vaccines utilizing MVA vector technology, should be based on the VN/1203 hemagglutinin. Furthermore, the recombinant MVA-HA-VN, as characterized in the present study, would be a promising candidate for such a vaccine.

Clinical evaluation to determine the appropriate paediatric formulation of a tick-borne encephalitis vaccine

Two dose-finding studies and one open label safety study with a paediatric FSME-IMMUN formulation were conducted in children and adolescents aged 1-15 years (N=3697). The 1.2 microg antigen dose was identified as the optimal dose, inducing high seroconversion rates following the primary vaccination series. Adolescents (aged 12-15 years) vaccinated with the optimal paediatric dose (1.2 microg) attained similarly high seroprotective rates to adults (aged 16-35 years) vaccinated with the 2.4 microg formulation of FSME-IMMUN. We concluded that the FSME-IMMUN paediatric vaccine formulation is safe and highly immunogenic, not only for children <12 years, but also for adolescents <16 years.

An inactivated West Nile Virus vaccine derived from a chemically synthesized cDNA system

A cDNA comprising the complete genome of West Nile Virus (WNV) was generated by chemical synthesis using published sequence data, independent of any preformed viral components. The synthetic WNV, produced by transfection of in vitro transcribed RNA into cell culture, exhibited undistinguishable biological properties compared to the corresponding animal-derived wild-type virus. No differences were found concerning viral growth in mammalian and insect cell lines and concerning expression of viral proteins in cells. There were also no significant differences in virulence in mice following intranasal challenge. After immunizations of mice with experimental vaccines derived from the synthetic and wild-type viruses, protection from lethal challenge was achieved with similar amounts of antigen. Both vaccine preparations also induced comparable levels of neutralizing antibodies in mice. In addition, the synthetic approach turned out to be very accurate, since the rescued WNV genome contained no undesired mutations. Thus, the first flavivirus based on chemical gene synthesis was indistinguishable from the parent virus. This demonstrates that virus isolates from animal sources are dispensable to derive seed viruses for vaccine production or research.

A whole virus pandemic influenza H1N1 vaccine is highly immunogenic and protective in active immunization and passive protection mouse models

The recent emergence and rapid spread of a novel swine-derived H1N1 influenza virus has resulted in the first influenza pandemic of this century. Monovalent vaccines have undergone preclinical and clinical development prior to initiation of mass immunization campaigns. We have carried out a series of immunogenicity and protection studies following active immunization of mice, which indicate that a whole virus, nonadjuvanted vaccine is immunogenic at low doses and protects against live virus challenge. The immunogenicity in this model was comparable to that of a whole virus H5N1 vaccine, which had previously been demonstrated to induce high levels of seroprotection in clinical studies. The efficacy of the H1N1 pandemic vaccine in protecting against live virus challenge was also seen to be equivalent to that of the H5N1 vaccine. The protective efficacy of the H1N1 vaccine was also confirmed using a severe combined immunodeficient (SCID) mouse model. It was demonstrated that mouse and guinea pig immune sera elicited following active H1N1 vaccination resulted in 100% protection of SCID mice following passive transfer of immune sera and lethal challenge. The immune responses to a whole virus pandemic H1N1 and a split seasonal H1N1 vaccine were also compared in this study. It was demonstrated that the whole virus vaccine induced a balanced Th-1 and Th-2 response in mice, whereas the split vaccine induced mainly a Th-2 response and only minimal levels of Th-1 responses. These data supported the initiation of clinical studies with the same low doses of whole virus vaccine that had previously been demonstrated to be immunogenic in clinical studies with a whole virus H5N1 vaccine.

Developing cell culture-derived pandemic vaccines

The growing prospect of avian influenza viruses achieving sustained interhuman transmission, combined with the recent emergence of a novel swine-origin A/H1N1 influenza strain, has brought the issue of influenza vaccine production capacity into sharp focus. It is becoming increasingly clear that traditional egg-based manufacturing processes may be insufficient to meet global vaccine demands in a pandemic situation that is caused by a highly pathogenic influenza virus. This review introduces the concepts of modern, cell culture-derived influenza vaccines and their manufacture, and explains the advantages of these vaccines in terms of both speed and efficiency of production as well as immunogenic efficacy. Vaccine production technologies using the mammalian cell lines Vero, MDCK and PER.C6, as well as the baculovirus/insect cell platform, are described in detail. Clinical data are provided from cell culture-derived vaccines that are at an advanced stage of development, and insights are provided into recent developments in the preclinical evaluation of more experimental technologies.

Seasonal influenza vaccine elicits heterosubtypic immunity against H5N1 that can be further boosted by H5N1 vaccination

Recent findings indicate that seasonal influenza vaccination or infection of healthy humans may contribute to heterosubtypic immunity against new influenza A subtypes, such as H5N1. Here, we investigated whether seasonal influenza vaccination in a mouse model could induce any immunity against the H5N1 subtype. It could be demonstrated that, largely due to the H1N1 component strain A/NewCaledonia/20/99, parenteral immunization of mice with a trivalent seasonal influenza vaccine elicited heterosubtype H5-reactive antibodies able to confer partial protection against H5N1 influenza virus infection. Furthermore, the trivalent seasonal influenza vaccine was found to be compatible with a whole virus H5N1 vaccine in a heterologous prime-boost immunization regimen, achieving superior efficacy compared to a single immunization with an equivalent low-dose of the H5N1 vaccine.

Vero cell platform in vaccine production: moving towards cell culture-based viral vaccines

The development of cell culture systems for virus propagation has led to major advances in virus vaccine development. Primary and diploid cell culture systems are now being replaced by the use of continuous cell lines (CCLs). These substrates are gaining increasing acceptance from regulatory authorities as improved screening technologies remove fears regarding their potential oncogenic properties. The Vero cell line is the most widely accepted CCL by regulatory authorities and has been used for over 30 years for the production of polio and rabies virus vaccines. The recent licensure of a Vero cell-derived live virus vaccine (ACAM2000, smallpox vaccine) has coincided with an explosion in the development of a range of new viral vaccines, ranging from live-attenuated pediatric vaccines against rotavirus infections to inactivated whole-virus vaccines against H5N1 pandemic influenza. These developments have illustrated the value of this cell culture platform in the rapid development of vaccines against a range of virus diseases.

A clinical trial of a whole-virus H5N1 vaccine derived from cell culture

BACKGROUND

Widespread infections of avian species with avian influenza H5N1 virus and its limited spread to humans suggest that the virus has the potential to cause a human influenza pandemic. An urgent need exists for an H5N1 vaccine that is effective against divergent strains of H5N1 virus.

METHODS

In a randomized, dose-escalation, phase 1 and 2 study involving six subgroups, we investigated the safety of an H5N1 whole-virus vaccine produced on Vero cell cultures and determined its ability to induce antibodies capable of neutralizing various H5N1 strains. In two visits 21 days apart, 275 volunteers between the ages of 18 and 45 years received two doses of vaccine that each contained 3.75 microg, 7.5 microg, 15 microg, or 30 microg of hemagglutinin antigen with alum adjuvant or 7.5 microg or 15 microg of hemagglutinin antigen without adjuvant. Serologic analysis was performed at baseline and on days 21 and 42.

RESULTS

The vaccine induced a neutralizing immune response not only against the clade 1 (A/Vietnam/1203/2004) virus strain but also against the clade 2 and 3 strains. The use of adjuvants did not improve the antibody response. Maximum responses to the vaccine strain were obtained with formulations containing 7.5 microg and 15 microg of hemagglutinin antigen without adjuvant. Mild pain at the injection site (in 9 to 27% of subjects) and headache (in 6 to 31% of subjects) were the most common adverse events identified for all vaccine formulations.

CONCLUSIONS

A two-dose vaccine regimen of either 7.5 microg or 15 microg of hemagglutinin antigen without adjuvant induced neutralizing antibodies against diverse H5N1 virus strains in a high percentage of subjects, suggesting that this may be a useful H5N1 vaccine. (ClinicalTrials.gov number, NCT00349141.)

Pre-clinical development of cell culture (Vero)-derived H5N1 pandemic vaccines

The rapid spread of avian influenza (H5N1) and its transmission to humans has raised the possibility of an imminent pandemic and concerns over the ability of standard influenza vaccine production methods to supply sufficient amounts of an effective vaccine. We report here on a robust and flexible strategy which uses wild-type virus grown in a continuous cell culture (Vero) system to produce an inactivated whole virus vaccine. Candidate vaccines based on clade 1 and clade 2 influenza H5N1 strains, produced at a variety of manufacturing scales, were demonstrated to be highly immunogenic in animal models without the need for adjuvant. The vaccines induce cross-neutralising antibodies and are protective in a mouse challenge model not only against the homologous virus but against other H5N1 strains, including those from other clades. These data indicate that cell culture-grown, whole virus vaccines, based on the wild-type virus, allow the rapid high-yield production of a candidate pandemic vaccine.