Promises and challenges of live-attenuated intranasal influenza vaccines across the age spectrum: a review

The cationic liposome CCS/C adjuvant induces immunity to influenza independently of the adaptor protein MyD88

Traditional non-living vaccines are often least effective in the populations that need them most, such as neonates and elderly adults. Vaccine adjuvants are one approach to boost the immunogenicity of antigens in populations with reduced immunity. Ideally, vaccine adjuvants will increase the seroconversion rates across the population, lead to stronger immune responses, and enable the administration of fewer vaccine doses. We previously demonstrated that a cationic liposomal formulation of the commercial influenza split virus vaccine (CCS/C-HA) enhanced cellular and humoral immunity to the virus, increased seroconversion rates, and improved survival after live virus challenge in a preclinical model, as compared to the commercial vaccine as is (F-HA). We now evaluated vaccine efficacy in different strains and sexes of mice and determined the role of innate immunity in the mechanism of action of the CCS/C adjuvant by testing the response of mice deficient in Toll-like receptors or the TLR/IL-1 adaptor protein MyD88 following immunization with CCS/C-HA vs. F-HA. Although TLR2- and TLR4-deficient mice responded to F-HA immunization, F-HA immunization failed to engender a significant immune response in the absence of MyD88. In contrast, immunization with the CCS/C-HA vaccine overcame the requirement for MyD88 in the response to the commercial vaccine and improved the immune responses and seroconversion rates in all strains of mice tested, including those deficient in TLR2 and TLR4.

Viral Inhibition of the IFN-Induced JAK/STAT Signalling Pathway: Development of Live Attenuated Vaccines by Mutation of Viral-Encoded IFN-Antagonists

The interferon (IFN) induced anti-viral response is amongst the earliest and most potent of the innate responses to fight viral infection. The induction of the Janus kinase/signal transducer and activation of transcription (JAK/STAT) signalling pathway by IFNs leads to the upregulation of hundreds of interferon stimulated genes (ISGs) for which, many have the ability to rapidly kill viruses within infected cells. During the long course of evolution, viruses have evolved an extraordinary range of strategies to counteract the host immune responses in particular by targeting the JAK/STAT signalling pathway. Understanding how the IFN system is inhibited has provided critical insights into viral virulence and pathogenesis. Moreover, identification of factors encoded by viruses that modulate the JAK/STAT pathway has opened up opportunities to create new anti-viral drugs and rationally attenuated new generation vaccines, particularly for RNA viruses, by reverse genetics.

Intranasal hydroxypropyl-β-cyclodextrin-adjuvanted influenza vaccine protects against sub-heterologous virus infection

Intranasal vaccination with inactivated influenza viral antigens is an attractive and valid alternative to currently available influenza (flu) vaccines; many of which seem to need efficient and safe adjuvant, however. In this study, we examined whether hydroxypropyl-β-cyclodextrin (HP-β-CD), a widely used pharmaceutical excipient to improve solubility and drug delivery, can act as a mucosal adjuvant for intranasal flu vaccines. We found that intranasal immunization of mice with hemagglutinin split- as well as inactivated whole-virion influenza vaccine with HP-β-CD resulted in secretion of antigen-specific IgA and IgGs in the airway mucosa and the serum as well. As a result, both HP-β-CD adjuvanted-flu intranasal vaccine protected mice against lethal challenge with influenza virus, equivalent to those induced by experimental cholera toxin-adjuvanted ones. Of note, intranasal use of HP-β-CD as an adjuvant induced significantly lower antigen-specific IgE responses than that induced by aluminum salt adjuvant. These results suggest that HP-β-CD may be a potent mucosal adjuvant for seasonal and pandemic influenza vaccine.

Development of a stable liquid formulation of live attenuated influenza vaccine

Vaccination is the most effective means of preventing influenza. However, the cost of producing annual seasonal influenza vaccines puts them out of reach for most developing countries. While live attenuated influenza vaccines are among the most efficacious and can be manufactured at low cost, they may require lyophilization to be stable enough for developing-country use, which adds a significant cost burden. The development of a liquid live attenuated seasonal influenza vaccine that is stable for around a year-the duration of an annual influenza season-would significantly improve not only the production output but also the use and accessibility of influenza vaccines in low-resource settings. In this study, potential stabilizing excipients were screened and optimized using the least stable influenza vaccine strain presently known, H1N1 (A/California/07/2009), as a model. The stability-conferring properties of the lead formulations were also tested with a Type B strain of influenza virus (B/Brisbane/60/2008). Stability was also evaluated with higher titers of influenza virus and exposure to agitation and freeze-thaw stresses to further confirm the stability of the lead formulations. Through this process, we identified a liquid formulation consisting of sucrose phosphate glutamate buffer with 1% arginine and 0.5% recombinant human serum albumin that provided storage stability of one year at 2-8°C for the influenza A and B strains tested.

Adjuvanted influenza vaccines

Influenza is one of the most common causes of human morbidity and mortality that is preventable by vaccination. Immunization with available vaccines provides incomplete protection against illness caused by influenza virus, especially in high-risk groups such as the elderly and young children. Thus, more efficacious vaccines are needed for the entire population, and all the more so for high-risk groups. One way to improve immune responses and protection is to formulate the vaccine with antigen carriers and/or adjuvants, which can play an important role in improving immune responses and delivery to antigen-presenting cells, especially for a vaccine like influenza that is based on protein antigens usually administered without a carrier or adjuvant. In this review, the authors present an overview of available vaccines, focusing on research and development of new adjuvants used in influenza vaccines, as well as adjuvanted influenza vaccines aimed to improve immune responses, protection and breadth of coverage for influenza.

An interspecific Nicotiana hybrid as a useful and cost-effective platform for production of animal vaccines

The use of transgenic plants to produce novel products has great biotechnological potential as the relatively inexpensive inputs of light, water, and nutrients are utilised in return for potentially valuable bioactive metabolites, diagnostic proteins and vaccines. Extensive research is ongoing in this area internationally with the aim of producing plant-made vaccines of importance for both animals and humans. Vaccine purification is generally regarded as being integral to the preparation of safe and effective vaccines for use in humans. However, the use of crude plant extracts for animal immunisation may enable plant-made vaccines to become a cost-effective and efficacious approach to safely immunise large numbers of farm animals against diseases such as avian influenza. Since the technology associated with genetic transformation and large-scale propagation is very well established in Nicotiana, the genus has attributes well-suited for the production of plant-made vaccines. However the presence of potentially toxic alkaloids in Nicotiana extracts impedes their use as crude vaccine preparations. In the current study we describe a Nicotiana tabacum and N. glauca hybrid that expresses the HA glycoprotein of influenza A in its leaves but does not synthesize alkaloids. We demonstrate that injection with crude leaf extracts from these interspecific hybrid plants is a safe and effective approach for immunising mice. Moreover, this antigen-producing alkaloid-free, transgenic interspecific hybrid is vigorous, with a high capacity for vegetative shoot regeneration after harvesting. These plants are easily propagated by vegetative cuttings and have the added benefit of not producing viable pollen, thus reducing potential problems associated with bio-containment. Hence, these Nicotiana hybrids provide an advantageous production platform for partially purified, plant-made vaccines which may be particularly well suited for use in veterinary immunization programs.

Vaccines for Seasonal and Pandemic Influenza

Seasonal influenza continues to have a huge annual impact in the United States, accounting for tens of millions of illnesses, hundreds of thousands of excess hospitalizations, and tens of thousands of excess deaths. Vaccination remains the mainstay for the prevention of influenza. In the United States, 2 types of influenza vaccine are currently licensed: trivalent inactivated influenza vaccine and live attenuated influenza vaccine. Both are safe and effective in the populations for which they are approved for use. Children, adults <65 years of age, and the elderly all receive substantial health benefits from vaccination. In addition, vaccination appears to be cost-effective, if not cost saving, across the age spectrum. Despite long-standing recommendations for the routine vaccination of persons in high-priority groups, US vaccination rates remain too low across all age groups. Important issues to be addressed include improving vaccine delivery to current and expanded target groups, ensuring timely availability of adequate vaccine supply, and development of even more effective vaccines. Development of a vaccine against potentially pandemic strains is an essential part of the strategy to control and prevent a pandemic outbreak. The use of existing technologies for influenza vaccine production would be the most straightforward approach, because these technologies are commercially available and licensing would be relatively simple. Approaches currently being tested include subvirion inactivated vaccines and cold-adapted, live attenuated vaccines. Preliminary results have suggested that, for some pandemic antigens, particularly H5, subvirion inactivated vaccines are poorly immunogenic, for reasons that are not clear. Data from evaluation of live pandemic vaccines are pending. Second-generation approaches designed to provide improved immune responses at lower doses have focused on adjuvants such as alum and MF59, which are currently licensed for influenza or other vaccines. Additional experimental approaches are required to achieve the ultimate goal for seasonal and pandemic influenza prevention--namely, the ability to generate broadly cross-reactive and durable protection in humans.

Role of influenza vaccine for healthy children in the US

Influenza infection is associated with significant morbidity and mortality in adults, but the highest attack rates for influenza regularly occur in children, particularly those in preschool and elementary school. The consequences of influenza in this younger population - increased rate of hospitalization in those younger than 2 years of age and serious associated morbidity - have been underestimated. Children are also the critical link for spreading influenza in the community. Recent data suggest that mass influenza vaccination of healthy children would not only protect recipients, but also may reduce the burden of influenza throughout the community. During the past 3 decades, efforts to control influenza have focused on the use of an injectable trivalent inactivated vaccine (TIV) in high-risk persons. The vaccine is 'safe' and effective, but its acceptance and uptake by patients and healthcare providers have been modest at best. A new intranasal, live-attenuated, trivalent cold-adapted influenza virus vaccine (CAIV-T) [FluMist] is 'safe', well tolerated, immunogenic, and efficacious in preventing influenza illness in healthy children. Compared with TIV, CAIV-T is easier to administer and should be more readily acceptable, particularly for mass immunization campaigns. CAIV-T also induces a broader immune response and has demonstrated protection against at least three different variant influenza strains. This vaccine is particularly well suited for routine immunization of children and thus offers the potential for greatly improved control of influenza. However, the acquisition cost per single dose of FluMist for the 2003-4 season ( approximate, equals 46 US dollars) significantly hampered its uptake both by practitioners and by managed care organizations, even despite a later approximate, equals 25 US dollars rebate offer. For the 2004-5 season, CAIV-T is likely to be only modestly more expensive (average wholesale price: 16.50 US dollars for non-returnable doses, 23 US dollars for returnable doses) than TIV. The practitioner must consider the benefits of FluMist compared with its likely higher vaccine cost and the issues of reimbursement among multiple insurers.

Vaccines administered simultaneously: directions for new combination vaccines based on an historical review of the literature

OBJECTIVES

The recognized benefits of administering vaccines simultaneously has encouraged vaccine producers to develop combination vaccines. If contemporary research and development can realize vaccines that achieve the current standards for safety, immunogenicity, and efficacy, other specific vaccine associations may also merit reconsideration as combination vaccines.

METHODS

An historical review of the vaccine association literature reveals two important themes: first, the programs of mass vaccination, in particular, the eradication of smallpox, sessions where multiple vaccines (other than the smallpox vaccine) were given concurrently, and the Expanded Programme on Immunization (EPI); and, second, the domain of travel vaccines, including travellers to a disease-endemic country (such as migrants, tourists, military personnel, or expatriates) and WHO requirements for international travellers.

RESULTS/CONCLUSIONS

Based on this historical review, combination vaccines worth reconsideration could fill epidemiologic niches in the EPI with, for instance, a measles--yellow fever, a measles--Japanese encephalitis or a pertussis-based paediatric combination rabies vaccine. Furthermore, other combinations could broaden protection against the pathogens responsible for meningitis, pneumonia, or enteric diseases. Nevertheless, complex issues such as necessity, feasibility, or affordability will ultimately determine if any one of these becomes a combination vaccine.

Live cold-adapted influenza A vaccine produced in Vero cell line

The African green monkey kidney (Vero) cell line was used as a substrate for the development of a live cold-adapted (ca) reassortant influenza vaccine. For that purpose, a new master strain was generated by an adaptation of the wild type (wt) A/Singapore/1/57 virus to growth at 25 degrees C in a Vero cell line. The resulting cold-adapted (ca) muster strain A/Singapore/1/57ca showed temperature sensitive (ts) phenotype and was attenuated in animal models and protective in the challenge experiments in ferrets. Two vaccine candidates of influenza A(H1N1) and A(H3N2) subtypes (6/2 reassortants) inheriting six genes coding internal proteins from the new master strain and the surface antigens hemagglutinin (HA) and neuraminidase (NA) from the epidemic viruses were obtained by a standard method of genetic reassortment. All steps of the vaccine preparation were done exclusively in Vero cells, including the isolation of the epidemic viruses. Both vaccine strains were used for immunization of young adult volunteers in a limited clinical trial and appeared to be safe, well tolerated and immunogenic after intranasal administration.

Influenza virus: immunity and vaccination strategies. Comparison of the immune response to inactivated and live, attenuated influenza vaccines

Influenza virus is a globally important respiratory pathogen which causes a high degree of morbidity and mortality annually. The virus is continuously undergoing antigenic change and thus bypasses the host's acquired immunity to influenza. Despite the improvement in antiviral therapy during the last decade, vaccination is still the most effective method of prophylaxis. Vaccination induces a good degree of protection (60-90% efficacy) and is well tolerated by the recipient. For those at risk of complications from influenza, annual vaccination is recommended due to the antigenic changes in circulating strains. However, there is still room for improvement in vaccine efficacy, long-lasting effect, ease of administration and compliance rates. The mucosal tissues of the respiratory tract are the main portal entry of influenza, and the mucosal immune system provides the first line of defence against infection. Secretory immunoglobulin A (SIgA) and IgM are the major neutralizing antibodies directed against mucosal pathogens. These antibodies work to prevent pathogen entry and can function intracellularly to inhibit replication of virus. This review describes influenza virus infection, epidemiology, clinical presentation and immune system response, particularly as it pertains to mucosal immunity and vaccine use. Specifically, this review provides an update of the current status on influenza vaccination and concentrates on the two main types of influenza vaccines currently in use, namely the cold-adapted vaccine (CAV) given intranasally/orally, and the inactivated vaccine (IV) delivered subcutanously or intramuscularly. The commercially available trivalent IV (TIV) elicits good serum antibody responses but induces poorly mucosal IgA antibody and cell-mediated immunity. In contrast, the CAV may elicit a long-lasting, broader immune (humoral and cellular) response, which more closely resembles natural immunity. The immune response induced by these two vaccines will be compared in this review.

Intranasal Cold-Adapted Influenza Virus Vaccine Combined with Inactivated Influenza Virus Vaccines

Although influenza vaccine delivery strategies have improved coverage rates to unprecedented levels nationally among persons aged 65 years and older, influenza remains one of the greatest vaccine-preventable threats to public health among elderly in the US. A new, intranasal live attenuated influenza vaccine (LAIV) was recently approved by the US FDA for use in persons aged 5-49 years, which excludes the elderly population. Limitations of immune response to inactivated influenza vaccine (IAIV) and effectiveness of current influenza vaccination strategies among the elderly suggest that a combined approach using LAIV and/or the IAIV in various permutations might benefit this group. We explore characteristics of the LAIV, data regarding its utility in protecting against influenza in the elderly, and challenges and opportunities regarding potential combined inactivated/live attenuated vaccination strategies for the elderly. Although LAIV appears to hold promise either alone or in combination with IAIV, large well conducted randomised trials are necessary to define further the role of LAIV in preventing influenza morbidity and mortality among the elderly. We also suggest that innovative vaccine coverage strategies designed to optimise prevention and control of influenza and minimise viral transmission in the community must accompany, in parallel, the acquisition of clinical trials data to best combat morbidity and mortality from influenza.

A decade after the generation of a negative-sense RNA virus from cloned cDNA - what have we learned?

Since the first generation of a negative-sense RNA virus entirely from cloned cDNA in 1994, similar reverse genetics systems have been established for members of most genera of the Rhabdo- and Paramyxoviridae families, as well as for Ebola virus (Filoviridae). The generation of segmented negative-sense RNA viruses was technically more challenging and has lagged behind the recovery of nonsegmented viruses, primarily because of the difficulty of providing more than one genomic RNA segment. A member of the Bunyaviridae family (whose genome is composed of three RNA segments) was first generated from cloned cDNA in 1996, followed in 1999 by the production of influenza virus, which contains eight RNA segments. Thus, reverse genetics, or the de novo synthesis of negative-sense RNA viruses from cloned cDNA, has become a reliable laboratory method that can be used to study this large group of medically and economically important viruses. It provides a powerful tool for dissecting the virus life cycle, virus assembly, the role of viral proteins in pathogenicity and the interplay of viral proteins with components of the host cell immune response. Finally, reverse genetics has opened the way to develop live attenuated virus vaccines and vaccine vectors.

Universal vaccination of healthy children against influenza: a role for the cold-adapted intranasal influenza vaccine

The incidence of influenza in children well exceeds that of the elderly and has been identified as the basis for 20% of doctor visits for children during the winter. The disease results in over 100 hospitalizations per 100000 person-months in children <2 years of age. Furthermore, children serve as the major vector in the community; thus, influenza in children results in significant costs to society. Although efficacious, the current intramuscular, inactivated influenza vaccine is infrequently used in children, and is currently targeted only at children at high risk and those who are household members of such individuals. Experts believe that vaccinating only high risk individuals has little impact on the cycle of annual epidemics, but that universal vaccination of children may very well have a substantial impact. Experimental data support this. A recently published cost-benefit analysis indicated that routine, school-aged vaccination through individual visits to a clinician would save 4 US dollars per child vaccinated. A group program such as a school-based one would save 35 US dollars. One obstacle to universal vaccination includes the real and perceived resistance to the addition of yet another annual injection to the already crowded schedule of routine childhood immunizations. Nearing licensure is an intranasal, live attenuated, cold-adapted intranasal influenza vaccine. Cold-adaptation prevents replication in the lower respiratory tract. Trials have demonstrated immunogenicity, safety, and tolerability in adults as well as children. Placebo-controlled trials have shown efficacy rates of 83 to 94%. This novel vaccine addresses obstacles to universal childhood immunization and would permit a program of routine use that would dramatically reduce transmission and stem epidemics of influenza.

Equine influenza virus infections: an update

Equine influenza is one of the most economically important contagious respiratory diseases of horses. In this paper the current state of knowledge of equine influenza virus and the most important aspects of these virus infections, e.g. epidemiology, clinical aspects, pathogenesis and pathology, immunity, diagnosis, treatment, management and vaccination, are reviewed with an emphasis on epidemiology, diagnosis and vaccinology. Many questions have remained and with the advent of improved technology new questions have arisen. Consequently, research priorities should be set in an attempt to answer them. Therefore, this review ends with some personal recommendations for important priorities for future research.

Generation of influenza A virus from cloned cDNAs--historical perspective and outlook for the new millenium

Influenza virus reverse genetics has reached a level of sophistication where one can confidently generate virus entirely from cloned DNAs. The new systems makes it feasible to study the molecular mechanisms of virus replication and pathogenicity, as well as to generate attenuated live virus vaccines, gene delivery vehicles, and possibly other RNA viruses from cloned cDNAs. During the next decade, one can anticipate the translation of influenza virus reverse genetics into biomedically relevant advances.

Nasal immunization with subunit proteosome influenza vaccines induces serum HAI, mucosal IgA and protection against influenza challenge

The immunogenicity of a mucosally delivered subunit influenza vaccine was assessed in mice. Split influenza virus vaccine (sFlu) was formulated with proteosomes (Pr-sFlu), administered intranasally, and the induced immunity was compared with the responses elicited by sFlu alone given either intramuscularly or intranasally. Intranasal (i.n.) immunization with Pr-sFlu induced specific serum IgG and hemagglutination inhibition (HAI) titers comparable to or better than those induced by intramuscular (i.m.) sFlu, and in contrast to sFlu alone, i.n. Pr-sFlu also induced high levels of influenza-specific IgA in lung and nasal washes. Mice receiving i.n. Pr-sFlu were completely protected against live virus challenge, as were mice immunized by injection with sFlu alone. The i.n. Pr-sFlu elicited cytokine responses polarized towards a type 1 phenotype whereas those elicited by sFlu alone were of a mixed type 1/type 2 phenotype. The data strongly suggest that i.n. proteosome-formulated influenza antigens are highly effective and are excellent candidates for a non-invasive human vaccine.

Reverse genetics of influenza virus

Reverse genetics of negative-sense RNA viruses, which enables one to generate virus entirely from cloned cDNA, has progressed rapidly over the past decade. However, despite the relative ease with which nonsegmented negative-sense RNA viruses can now be produced from plasmids, the ability to generate viruses with segmented genomes has lagged considerably, largely because of the inherent technical difficulties in providing all viral RNAs and proteins from cloned cDNA. A breakthrough in reverse genetics technology in the influenza virus field came in 1999, when we (Neumann et al., 1999, Proc. Natl. Acad. Sci. USA 96, 9345-9350) and others (Fodor et al., 1999, J. Virol. 73, 9679-9682) exploited a new approach to viral RNA production. In this review, we discuss the background for this advance, the systems that are now available for the generation of influenza viruses, and the implications of these developments for the future of virus research.

Nosocomial outbreak of influenza virus A (H3N2) infection in a solid organ transplant department

BACKGROUND

There is a strong body of evidence in favor of influenza virus immunization in solid organ recipients. However, little attention has been devoted to other reservoirs, such as the patients' relatives and, at the time of hospital admission, to the healthcare workers.

METHODS

Analysis of the epidemiology of an outbreak of nosocomial influenza A in a solid organ transplant unit.

RESULTS

Four cases of influenza A virus infection were reported during a short 4-day outbreak in a 12 single-room transplant unit. None of the patients had been immunized against influenza. Three patients had not been visited by their relatives between admission and influenza infection. Three nurses, among the 27 healthcare workers, presented with clinical flu symptoms at times consistent with nosocomial transmission.

CONCLUSIONS

Because the prevention of influenza infection by vaccination warrants a global strategy to target the different reservoirs, we suggest that the modern policy of vaccinating solid organ patients should be extended both to their relatives and to the healthcare workers of transplant units.

Making vaccines more acceptable--methods to prevent and minimize pain and other common adverse events associated with vaccines

The growing abundance of highly immunogenic vaccines has arrived with a burden of pain, distress, and common adverse reactions that in turn may interfere with parental compliance and aggravate anti-vaccine sentiment. In a study of 150 children in each of 2 age-groups, we found that approximately 20% of the subjects suffered serious distress or worse. During the procedural phase, approximately 90% of the 15-to-18 month old children and 45% of the 4-to-6 year old children showed serious distress or worse. To address non-adherence with pediatric vaccine schedules, we must consider all of the possible issues that might prevent a parent from taking a child to a health care provider for vaccination. In that same study we identified useful predictors for both preparatory and procedural distress - predictors that might be used in identifying children who might benefit from preventive interventions. Vaccine providers might consider a variety of interventions. Attitude, empathy, instruction, and practice have all been shown to have a salutatory effect upon pain and anxiety with medical procedures in general and specifically with vaccinations. Distraction has also been found to be an effective method for distress and pain prevention in children. More formal methods of clinical hypnosis which combine a deep state of relaxation with focused imagery and suggestion have also been found to be effective in helping children and adolescents prepare for, cope with, and tolerate the pain and anxiety associated with medical procedures. So-called 'sugar nipples' delivering small amounts of sucrose orally at the time of a painful procedure in an infant has been not been shown to decrease vaccination pain and studies on refrigerant topical anesthetics are mixed. Studies have found a eutectic mixture of 2.5% lidocaine and 2.5% prilocaine (EMLA) effective in providing adequate local anesthesia in children, but it suffers from problems in practical application. Studies with various injection techniques have not identified ready solutions, and although jet injection appears to provoke less anxiety and cause less immediate pain, studies also indicate a somewhat greater incidence of delayed local reactogenicity including soreness and edema. Other measures to prevent or rapidly treat other common adverse events have been shown effective and should be considered as well.