Virus-Vectored Influenza Virus Vaccines

Despite the availability of an inactivated vaccine that has been licensed for >50 years, the influenza virus continues to cause morbidity and mortality worldwide. Constant evolution of circulating influenza virus strains and the emergence of new strains diminishes the effectiveness of annual vaccines that rely on a match with circulating influenza strains. Thus, there is a continued need for new, efficacious vaccines conferring cross-clade protection to avoid the need for biannual reformulation of seasonal influenza vaccines. Recombinant virus-vectored vaccines are an appealing alternative to classical inactivated vaccines because virus vectors enable native expression of influenza antigens, even from virulent influenza viruses, while expressed in the context of the vector that can improve immunogenicity. In addition, a vectored vaccine often enables delivery of the vaccine to sites of inductive immunity such as the respiratory tract enabling protection from influenza virus infection. Moreover, the ability to readily manipulate virus vectors to produce novel influenza vaccines may provide the quickest path toward a universal vaccine protecting against all influenza viruses. This review will discuss experimental virus-vectored vaccines for use in humans, comparing them to licensed vaccines and the hurdles faced for licensure of these next-generation influenza virus vaccines.     

Targeting Antigens for Universal Influenza Vaccine Development

Traditional influenza vaccines generate strain-specific antibodies which cannot provide protection against divergent influenza virus strains. Further, due to frequent antigenic shifts and drift of influenza viruses, annual reformulation and revaccination are required in order to match circulating strains. Thus, the development of a universal influenza vaccine (UIV) is critical for long-term protection against all seasonal influenza virus strains, as well as to provide protection against a potential pandemic virus. One of the most important strategies in the development of UIVs is the selection of optimal targeting antigens to generate broadly cross-reactive neutralizing antibodies or cross-reactive T cell responses against divergent influenza virus strains. However, each type of target antigen for UIVs has advantages and limitations for the generation of sufficient immune responses against divergent influenza viruses. Herein, we review current strategies and perspectives regarding the use of antigens, including hemagglutinin, neuraminidase, matrix proteins, and internal proteins, for universal influenza vaccine development.     

Universally Immune: How Infection Permissive Next Generation Influenza Vaccines May Affect Population Immunity and Viral Spread

Next generation influenza vaccines that target conserved epitopes are becoming a clinical reality but still have challenges to overcome. Universal next generation vaccines are considered a vital tool to combat future pandemic viruses and have the potential to vastly improve long-term protection against seasonal influenza viruses. Key vaccine strategies include HA-stem and T cell activating vaccines; however, they could have unintended effects for virus adaptation as they recognise the virus after cell entry and do not directly block infection. This may lead to immune pressure on residual viruses. The potential for immune escape is already evident, for both the HA stem and T cell epitopes, and mosaic approaches for pre-emptive immune priming may be needed to circumvent key variants. Live attenuated influenza vaccines have not been immunogenic enough to boost T cells in adults with established prior immunity. Therefore, viral vectors or peptide approaches are key to harnessing T cell responses. A plethora of viral vector vaccines and routes of administration may be needed for next generation vaccine strategies that require repeated long-term administration to overcome vector immunity and increase our arsenal against diverse influenza viruses.     

An overview of the regulation of influenza vaccines in the United States

Influenza virus vaccines are unique among currently licensed viral vaccines. The vaccines designed to protect against seasonal influenza illness must be updated periodically in an effort to match the vaccine strain with currently circulating viruses, and the vaccine manufacturing timeline includes multiple, overlapping processes with a very limited amount of flexibility. In the United States (U.S.), over 150 million doses of seasonal trivalent and quadrivalent vaccine are produced annually, a mammoth effort, particularly in the context of a vaccine with components that usually change on a yearly basis. In addition, emergence of an influenza virus containing an HA subtype that has not recently circulated in humans is an ever present possibility. Recently, pandemic influenza vaccines have been licensed, and the pathways for licensure of pandemic vaccines and subsequent strain updating have been defined. Thus, there are formidable challenges for the regulation of currently licensed influenza vaccines, as well as for the regulation of influenza vaccines under development. This review describes the process of licensing influenza vaccines in the U.S., the process and steps involved in the annual updating of seasonal influenza vaccines, and some recent experiences and regulatory challenges faced in development and evaluation of novel influenza vaccines.     

Influenza Vaccines: A Moving Interdisciplinary Field

Vaccination is by far the most effective way of preventing morbidity and mortality due to infection of the upper respiratory tract by influenza virus. Current vaccines require yearly vaccine updates as the influenza virus can escape vaccine-induced humoral immunity due to the antigenic variability of its surface antigens. In case of a pandemic, new vaccines become available too late with current vaccine practices. New technologies that allow faster production of vaccine seed strains in combination with alternative production platforms and vaccine formulations may shorten the time gap between emergence of a new influenza virus and a vaccine becoming available. Adjuvants may allow antigen-sparing, allowing more people to be vaccinated with current vaccine production capacity. Adjuvants and universal vaccines can target immune responses to more conserved influenza epitopes, which eventually will result in broader protection for a longer time. In addition, further immunological studies are needed to gain insights in the immune features that contribute to protection from influenza-related disease and mortality, allowing redefinition of correlates of protection beyond virus neutralization in vitro.     

Pandemic influenza 1918 H1N1 and 1968 H3N2 DNA vaccines induce cross-reactive immunity in ferrets against infection with viruses drifted for decades

Please cite this paper as: Bragstad et al. (2010) Pandemic influenza 1918 H1N1 and 1968 H3N2 DNA vaccines induce cross‐reactive immunity in ferrets against infection with viruses drifted for decades. Influenza and Other Respiratory Viruses 5(1), 13–23. Background Alternative influenza vaccines and vaccine production forms are needed as the conventional protein vaccines do not induce broad cross‐reactivity against drifted strains. Furthermore, fast vaccine production is especially important in a pandemic situation, and broader vaccine reactivity would diminish the need for frequent change in the vaccine formulations. Objective In this study, we compared the ability of pandemic influenza DNA vaccines to induce immunity against distantly related strains within a subtype with the immunity induced by conventional trivalent protein vaccines against homologous virus challenge. Methods Ferrets were immunised by particle‐mediated epidermal delivery (gene gun) with DNA vaccines based on the haemagglutinin (HA) and neuraminidase (NA) and/or the matrix (M) and nucleoprotein genes of the 1918 H1N1 Spanish influenza pandemic virus or the 1968 H3N2 Hong Kong influenza pandemic virus. The animals were challenged with contemporary H1N1 or H3N2 viruses. Results We demonstrated that DNA vaccines encoding proteins of the original 1918 H1N1 pandemic virus induced protective cross‐reactive immune responses in ferrets against infection with a 1947 H1N1 virus and a recent 1999 H1N1 virus. Similarly, a DNA vaccine, based on the HA and NA of the 1968 H3N2 pandemic virus, induced cross‐reactive immune responses against a recent 2005 H3N2 virus challenge. Conclusions DNA vaccines based on pandemic or recent seasonal influenza genes induced cross‐reactive immunity against contemporary virus challenge as good as or superior to contemporary conventional trivalent protein vaccines. This suggests a unique ability of influenza DNA to induce cross‐protective immunity against both contemporary and long‐time drifted viruses.     

The Potential Advantages and Requirements of Live Attenuated Influenza Virus Vaccines*

Summary: :The potential advantages and requirements of live attenuated influenza virus vaccines. J. S. Mackenzie, Aust. N.Z. J. Med., 1977, 7, pp. 431–437. Live attenuated influenza A virus vaccines are potentially the most efficient and effective method of immunization against epidemic influenza, and offer the only feasible means of mass vaccination at a socially acceptable cost. The advantage of live virus vaccines are described and compared with killed virus vaccines in terms of immune responses, protection and commercial production. The most frequently considered methods of attenuation and their individual drawbacks are discussed with speculation on the future development and rationale of master vaccine strains. Recommended minimal requirements of master vaccine strains and candidate live vaccines are presented as a basis for their eventual evaluation by licensing authorities.     

IL-15 adjuvanted multivalent vaccinia-based universal influenza vaccine requires CD4+ T cells for heterosubtypic protection

Current influenza vaccines are ineffective against novel viruses and the source or the strain of the next outbreak of influenza is unpredictable; therefore, establishing universal immunity by vaccination to limit the impact of influenza remains a high priority. To meet this challenge, a novel vaccine has been developed using the immunogenic live vaccinia virus as a vaccine vector, expressing multiple H5N1 viral proteins (HA, NA, M1, M2, and NP) together with IL-15 as a molecular adjuvant. Previously, this vaccine demonstrated robust sterile cross-clade protection in mice against H5 influenza viruses, and herein its use has been extended to mediate heterosubtypic immunity toward viruses from both group 1 and 2 HA lineages. The vaccine protected mice against lethal challenge by increasing survival and significantly reducing lung viral loads against the most recent human H7N9, seasonal H3N2, pandemic-2009 H1N1, and highly pathogenic H7N7 influenza A viruses. Influenza-specific antibodies elicited by the vaccine failed to neutralize heterologous viruses and were unable to confer protection by passive transfer. Importantly, heterologous influenza-specific CD4⁺ and CD8⁺ T-cell responses that were elicited by the vaccine were effectively recalled and amplified following viral challenge in the lungs and periphery. Selective depletion of T-cell subsets in the immunized mice revealed an important role for CD4⁺ T cells in heterosubtypic protection, despite low sequence conservation among known MHC-II restricted epitopes across different influenza viruses. This study illustrates the potential utility of our multivalent Wyeth/IL-15/5Flu as a universal influenza vaccine with a correlate of protective immunity that is independent of neutralizing antibodies.Influenza causes widespread infection during seasonal epidemics and occasional worldwide pandemics despite available vaccines. The subtype of future outbreaks or pandemic influenza strains is unpredictable as is its source, evident from the most recent H7N9 outbreak from poultry in China, the variant H3N2 outbreak from swine in the United States in 2012, the H1N1 worldwide pandemic of 2009, and the highly pathogenic avian influenza (HPAI) H5N1 in 1997 from domestic poultry. Therefore, the development of a successful universal vaccination strategy is urgently needed.Universal protection requires heterosubtypic immunity (HSI), whereby vaccination against one influenza virus cross-protects against novel and emerging strains that could potentially be mediated by multiple adaptive immune mechanisms. T cells are potent mediators of HSI, because these cells typically recognize peptide epitopes derived from internal proteins of influenza virus, which are naturally more conserved than surface HA and NA across different strains and even serologically distinct viral subtypes. Because of sequence conservation of the majority of T-cell epitopes between different influenza viruses, cross-reactive T-cell responses have been detected in healthy seronegative individuals against H5N1 and pandemic H1N1-2009 viruses (1, 2).Previously, we generated a multivalent vaccinia virus-based H5N1 influenza vaccine, which demonstrated effective cross-clade immunity against lethal H5N1 challenges. This vaccine expresses five H5N1-derived influenza proteins (HA, NA, M1, M2, and NP), in combination with the immune stimulatory cytokine IL-15 (3) that increases long-term memory responses, along with enhanced T-cell, B-cell, and NK cell functions, including cytokine production and survival. Despite the use of live vaccine vectors being generally constrained in immune-compromised individuals, the vaccine vector (Wyeth/IL-15) has been proven safe and effective in primates and immune-deficient mice (4).A cell-culture–derived, live vaccine vector that encodes full-length influenza proteins with inherent capacity to access MHC-I and II processing pathways to establish robust influenza-specific T-cell responses is an excellent approach to overcome issues related to population-wide MHC polymorphism and egg-based production methods for HPAI vaccines. Herein, we extend the use of Wyeth/IL-15/5Flu vaccine against multiple human influenza viruses of different HA subtypes, including the highly pathogenic H7N7, pandemic H1N1-2009, seasonal H3N2, and the most recent human H7N9 viruses. The vaccine proved effective against all of the heterologous strains tested, and the immunological mechanisms of protection were investigated to decipher correlates of immunity.     

Vaccination with a synthetic peptide from the influenza virus hemagglutinin provides protection against distinct viral subtypes

Current influenza virus vaccines protect mostly against homologous virus strains; thus, regular immunization with updated vaccine formulations is necessary to guard against the virus' hallmark remodeling of regions that mediate neutralization. Development of a broadly protective influenza vaccine would mark a significant advance in human infectious diseases research. Antibodies with broad neutralizing activity (nAbs) against multiple influenza virus strains or subtypes have been reported to bind the stalk of the viral hemagglutinin, suggesting that a vaccine based on this region could elicit a broadly protective immune response. Here we describe a hemagglutinin subunit 2 protein (HA2)-based synthetic peptide vaccine that provides protection in mice against influenza viruses of the structurally divergent subtypes H3N2, H1N1, and H5N1. The immunogen is based on the binding site of the recently described nAb 12D1, which neutralizes H3 subtype viruses, demonstrates protective activity in vivo, and, in contrast to a majority of described nAbs, appears to bind to residues within a single α-helical portion of the HA2 protein. Our data further demonstrate that the specific design of our immunogen is integral in the induction of broadly active anti-hemagglutinin antibodies. These results provide proof of concept for an HA2-based influenza vaccine that could diminish the threat of pandemic influenza disease and generally reduce the significance of influenza viruses as human pathogens.     

Comparative safety, immunogenicity, and efficacy of several anti-H5N1 influenza experimental vaccines in a mouse and chicken models (Testing of killed and live H5 vaccine)

Please cite this paper as: Gambaryan et al. (2011) Comparative safety, immunogenicity, and efficacy of several anti‐H5N1 influenza experimental vaccines in a mouse and chicken models. Parallel testing of killed and live H5 vaccine. Influenza and Other Respiratory Viruses 6(3), 188–195. Objective Parallel testing of inactivated (split and whole virion) and live vaccine was conducted to compare the immunogenicity and protective efficacy against homologous and heterosubtypic challenge by H5N1 highly pathogenic avian influenza virus. Method Four experimental live vaccines based on two H5N1 influenza virus strains were tested; two of them had hemagglutinin (HA) of A/Vietnam/1203/04 strain lacking the polybasic HA cleavage site, and two others had hemagglutinins from attenuated H5N1 virus A/Chicken/Kurgan/3/05, with amino acid substitutions of Asp54/Asn and Lys222/Thr in HA1 and Val48/Ile and Lys131/Thr in HA2 while maintaining the polybasic HA cleavage site. The neuraminidase and non‐glycoprotein genes of the experimental live vaccines were from H2N2 cold‐adapted master strain A/Leningrad/134/17/57 (VN‐Len and Ku‐Len) or from the apathogenic H6N2 virus A/Gull/Moscow/3100/2006 (VN‐Gull and Ku‐Gull). Inactivated H5N1 and H1N1 and live H1N1 vaccine were used for comparison. All vaccines were applied in a single dose. Safety, immunogenicity, and protectivity against the challenge with HPAI H5N1 virus A/Chicken/Kurgan/3/05 were estimated. Results All experimental live H5 vaccines tested were apathogenic as determined by weight loss and conferred more than 90% protection against lethal challenge with A/Chicken/Kurgan/3/05 infection. Inactivated H1N1 vaccine in mice offered no protection against challenge with H5N1 virus, while live cold‐adapted H1N1 vaccine reduced the mortality near to zero level. Conclusions The high yield, safety, and protectivity of VN‐Len and Ku‐Len made them promising strains for the production of inactivated and live vaccines against H5N1 viruses.     

Hallmarks of CD4 T cell immunity against influenza

The mechanisms responsible for heterosubtypic immunity to influenza virus are not well understood but might hold the key for new vaccine strategies capable of providing lasting protection against both seasonal and pandemic strains. Memory CD4 T cells are capable of providing substantial protection against influenza both through direct effector mechanisms and indirectly through regulatory and helper functions. Here, we discuss the broad impact of memory CD4 T cells on heterosubtypic immunity against influenza and the prospects of translating findings from animal models into improved human influenza vaccines.     

Nanoparticles in influenza subunit vaccine development: Immunogenicity enhancement

The threat of novel influenza infections has sparked research efforts to develop subunit vaccines that can induce a more broadly protective immunity by targeting selected regions of the virus. In general, subunit vaccines are safer but may be less immunogenic than whole cell inactivated or live attenuated vaccines. Hence, novel adjuvants that boost immunogenicity are increasingly needed as we move toward the era of modern vaccines. In addition, targeting, delivery, and display of the selected antigens on the surface of professional antigen‐presenting cells are also important in vaccine design and development. The use of nanosized particles can be one of the strategies to enhance immunogenicity as they can be efficiently recognized by antigen‐presenting cells. They can act as both immunopotentiators and delivery system for the selected antigens. This review will discuss on the applications, advantages, limitations, and types of nanoparticles (NPs) used in the preparation of influenza subunit vaccine candidates to enhance humoral and cellular immune responses.     

Determination of H5N1 vaccine potency using reference antisera from heterologous strains of influenza

Please cite this paper as: Vodeiko and Weir (2011). Determination of H5N1 vaccine potency using reference antisera from heterologous strains of influenza. Influenza and Other Respiratory Viruses 6(3), 176–187. Background Standardization of inactivated influenza vaccines by hemagglutinin (HA) content is performed by the single radial immunodiffusion (SRID) method. Regulatory agencies prepare, calibrate, and distribute SRID reagent standards necessary for testing of seasonal influenza vaccines, and a similar process is used to produce potency reagents for candidate pandemic influenza vaccines that are manufactured for emergency stockpiles. Objectives Because of the concerns in generating a timely strain‐specific potency antiserum for an emerging pandemic virus, we evaluated the feasibility of using heterologous potency reference antiserum as a replacement for a strain‐specific (homologous) antiserum in the SRID potency assay for stockpiled H5N1 vaccines. Results The results indicate that a heterologous H5N1 antiserum can be used to determine the accurate potency of inactivated H5N1 influenza vaccines. Additionally, when H5N1 vaccine was subjected to an accelerated stability protocol, both homologous and heterologous antisera provided similar measurements of vaccine potency decline. Limitations to the heterologous antiserum approach to potency determination were shown by the inability of antiserum to recent seasonal H1N1 viruses to work in an SRID assay with the 2009 pandemic H1N1 A/California/07/2009 antigen. Conclusions The data demonstrate the feasibility of using heterologous antiserum for potency determination of at least some candidate vaccines in case of a shortage or delay of homologous antiserum. Further, the results suggest the prudence of stockpiling a broad library of potency reagents including many strains of influenza viruses with pandemic potential to provide an added measure of assurance that reagent production would not be a bottleneck to vaccine production during a pandemic.     

Long‐term vaccine‐induced heterologous protection against H5N1 influenza viruses in the ferret model

Please cite this paper as: Ducatez et al. (2012) Long‐term vaccine‐induced heterologous protection against H5N1 influenza viruses in the ferret model. Influenza and Other Respiratory Viruses 7(4), 506–512. Background Highly pathogenic H5N1 influenza viruses reemerged in humans in 2003 and have caused fatal human infections in Asia and Africa as well as ongoing outbreaks in poultry. These viruses have evolved substantially and are now so antigenically varied that a single vaccine antigen may not protect against all circulating strains. Nevertheless, studies have shown that substantial cross‐reactivity can be achieved with H5N1 vaccines. These studies have not, however, addressed the issue of duration of such cross‐reactive protection. Objectives To directly address this using the ferret model, we used two recommended World Health Organization H5N1 vaccine seed strains – A/Vietnam/1203/04 (clade 1) and A/duck/Hunan/795/02 (clade 2.1) – seven single, double, or triple mutant viruses based on A/Vietnam/1203/04, and the ancestral viruses A and D, selected from sequences at nodes of the hemagglutinin and neuraminidase gene phylogenies to represent antigenically diverse progeny H5N1 subclades as vaccine antigens. Results All inactivated whole‐virus vaccines provided full protection against morbidity and mortality in ferrets challenged with the highly pathogenic H5N1 strain A/Vietnam/1203/04 5 months and 1 year after immunization. Conclusion If an H5N1 pandemic was to arise, and with the hypothesis that one can extrapolate the results from three doses of a whole‐virion vaccine in ferrets to the available split vaccines for use in humans, the population could be efficiently immunized with currently available H5N1 vaccines, while the homologous vaccine is under production.     

Confronting the avian influenza threat: vaccine development for a potential pandemic

Sporadic human infection with avian influenza viruses has raised concern that reassortment between human and avian subtypes could generate viruses of pandemic potential. Vaccination is the principal means to combat the impact of influenza. During an influenza pandemic the immune status of the population would differ from that which exists during interpandemic periods. An emerging pandemic virus will create a surge in worldwide vaccine demand and new approaches in immunisation strategies may be needed to ensure optimum protection of unprimed individuals when vaccine antigen may be limited. The manufacture of vaccines from pathogenic avian influenza viruses by traditional methods is not feasible for safety reasons as well as technical issues. Strategies adopted to overcome these issues include the use of reverse genetic systems to generate reassortant strains, the use of baculovirus-expressed haemagglutinin or related non-pathogenic avian influenza strains, and the use of adjuvants to enhance immunogenicity. In clinical trials, conventional surface-antigen influenza virus vaccines produced from avian viruses have proved poorly immunogenic in immunologically naive populations. Adjuvanted or whole-virus preparations may improve immunogenicity and allow sparing of antigen.     

Prior contacts with the 2000–2003 seasonal vaccines extends the 2009 pandemic A/H1N1 vaccine-specific immune protection to non-humoral compartments

Activating different adaptive immune component is required to confer long-time protection against influenza viruses. By investigating the co-mobilization of immune compartments following A/H1N1 2009 pandemic vaccine (A(H1N1)pdm09 influenza vaccine–Panenza^®, Sanofi Pasteur), we show that multiple vaccination with 2000-2003 seasonal influenza vaccines leads to a broader immune repertoire than the one theoretically expected by vaccine strains. Moreover, in case of contact with strains previously encountered, the A(H1N1)pdm09-specific immune response is extended to non-humoral immune components (i.e. CD8+ and/or CD4+ T-cells response).     

A liposome-displayed hemagglutinin vaccine platform protects mice and ferrets from heterologous influenza virus challenge

Recombinant influenza virus vaccines based on hemagglutinin (HA) hold the potential to accelerate production timelines and improve efficacy relative to traditional egg-based platforms. Here, we assess a vaccine adjuvant system comprised of immunogenic liposomes that spontaneously convert soluble antigens into a particle format, displayed on the bilayer surface. When trimeric H3 HA was presented on liposomes, antigen delivery to macrophages was improved in vitro, and strong functional antibody responses were induced following intramuscular immunization of mice. Protection was conferred against challenge with a heterologous strain of H3N2 virus, and naive mice were also protected following passive serum transfer. When admixed with the particle-forming liposomes, immunization reduced viral infection severity at vaccine doses as low as 2 ng HA, highlighting dose-sparing potential. In ferrets, immunization induced neutralizing antibodies that reduced the upper respiratory viral load upon challenge with a more modern, heterologous H3N2 viral strain. To demonstrate the flexibility and modular nature of the liposome system, 10 recombinant surface antigens representing distinct influenza virus strains were bound simultaneously to generate a highly multivalent protein particle that with 5 ng individual antigen dosing induced antibodies in mice that specifically recognized the constituent immunogens and conferred protection against heterologous H5N1 influenza virus challenge. Taken together, these results show that stable presentation of recombinant HA on immunogenic liposome surfaces in an arrayed fashion enhances functional immune responses and warrants further attention for the development of broadly protective influenza virus vaccines.

Influenza virus is a persistent global health concern, mainly because the efficacy of current vaccines is suboptimal. The narrow breadth of protection and rapid waning of vaccination-induced antibodies along with the circulation of variant viruses necessitates annual reformulation and readministration of seasonal influenza virus vaccines. Seasonal influenza epidemics result in a global total of 3 to 5 million severe infections each year, with 290,000 to 650,000 deaths (1). The viral envelope contains two major surface glycoproteins, hemagglutinin (HA) and neuraminidase (NA), of which there are many antigenically distinct subtypes (H1-18, N1-11) (2, 3). Both proteins are subject to antigenic drift; the selection of advantageous mutations that alters antigenicity and promotes escape from preexisting immunity. In addition to seasonal epidemics, novel forms of the virus have arisen throughout history to cause pandemics with high morbidity and mortality rates. These strains generally arise by antigenic shift, a process through which two different influenza virus strains reassort their genomes within host cells. This results in an influenza virus strain to which the human population is largely naive (4, 5). The influenza virus''s capacity to circumvent immune recognition through antigenic change has been a significant barrier to the development of long-lasting immunity and highly efficacious vaccines.Currently, seasonal influenza vaccination relies on a global viral surveillance system and predictive models that determine which strains will be incorporated into the seasonal vaccine each year. However, seasonal vaccine efficacy varies significantly depending upon the degree of matching between the predicted and circulating strains and does not provide significant protection when variant seasonal or pandemic strains emerge. Most seasonal influenza vaccines are still produced in embryonated chicken eggs, which necessitates a protracted vaccine production timeline and can result in egg-adapted vaccine strains that are antigenically dissimilar from circulating strains (6, 7). To address this, future vaccine strategies should be developed that can either yield a more rapid production process or protect against a more extensive repertoire of influenza virus strains, ideally including strains that are yet to arise. Both approaches favor the application of recombinant influenza virus antigens, with molecular structures that can be precisely controlled and modified. Recombinant antigens have proven safe and effective in the Flublok vaccine (8), and several studies have assessed epitope-based vaccine strategies based on conserved protein sequences in the stalk region (9, 10) and head region (11) of recombinant HA antigens. However, for many experimental recombinant vaccines to achieve a sufficient degree of immunogenicity, recombinant antigens must be administered in conjunction with an adjuvant to increase the magnitude of the immune response that they elicit. While regulatory agencies have approved several adjuvanted influenza vaccines for clinical use (12, 13), existing adjuvants may not be optimum for recombinant proteins. New adjuvants are being developed including nanoparticle-based carriers for recombinant antigens (14, 15). Liposomes, in particular, have been developed as vaccine adjuvants (16) and have been assessed with recombinant HA in preclinical studies (17–19). In this study, to enhance liposome immunogenicity, a synthetic monophosphoryl lipid A (MPLA) variant, phosphorylated hexaacyl disaccharide (PHAD), was incorporated into the lipid membrane. MPLA is used as a component of AS01, a liposomal adjuvant currently included in the Shingrix vaccine for Herpes Zoster (20, 21).We have developed an adjuvant system based on liposomes containing cobalt-porphyrin phospholipid (CoPoP). CoPoP provides a methodology that results in biostable binding due to the sequestration of His-tagged antigens directly within the bilayer (22). The CoPoP contained in the liposomal membranes results in rapid binding of His-tag modified recombinant antigens at room temperature (RT) with straightforward coincubation. When used in this way for immunization, CoPoP particles have been shown to enhance antibody responses to recombinant antigens derived from several pathogens (23–26). CoPoP has entered human clinical trials as a component of a SARS-CoV-2 vaccine (ClinicalTrials.gov Identifier: {"type":"clinical-trial","attrs":{"text":"NCT04783311","term_id":"NCT04783311"}}NCT04783311). In this study, we assess whether CoPoP can contribute to a platform for influenza virus vaccines. Recombinant HA trimers with trimerizing foldon domains from T4 bacteriophage fibritin were used to generate antigen associated with CoPoP liposome surfaces with conformation putatively replicating the trimers formed by native HA complexes (27, 28).     

Modified Vaccinia Virus Ankara (MVA) as Production Platform for Vaccines against Influenza and Other Viral Respiratory Diseases

Respiratory viruses infections caused by influenza viruses, human parainfluenza virus (hPIV), respiratory syncytial virus (RSV) and coronaviruses are an eminent threat for public health. Currently, there are no licensed vaccines available for hPIV, RSV and coronaviruses, and the available seasonal influenza vaccines have considerable limitations. With regard to pandemic preparedness, it is important that procedures are in place to respond rapidly and produce tailor made vaccines against these respiratory viruses on short notice. Moreover, especially for influenza there is great need for the development of a universal vaccine that induces broad protective immunity against influenza viruses of various subtypes. Modified Vaccinia Virus Ankara (MVA) is a replication-deficient viral vector that holds great promise as a vaccine platform. MVA can encode one or more foreign antigens and thus functions as a multivalent vaccine. The vector can be used at biosafety level 1, has intrinsic adjuvant capacities and induces humoral and cellular immune responses. However, there are some practical and regulatory issues that need to be addressed in order to develop MVA-based vaccines on short notice at the verge of a pandemic. In this review, we discuss promising novel influenza virus vaccine targets and the use of MVA for vaccine development against various respiratory viruses.     

Influenza: the virus and prophylaxis with inactivated influenza vaccine in ��at risk�� groups, including COPD patients

Influenza is a major respiratory pathogen, which exerts a huge human and economic toll on society. Influenza is a vaccine preventable disease, however, the vaccine strains must be annually updated due to the continuous antigenic changes in the virus. Inactivated influenza vaccines have been used for over 50 years and have an excellent safety record. Annual vaccination is therefore recommended for all individuals with serious medical conditions, like COPD, and protects the vaccinee against influenza illness and also against hospitalization and death. In COPD patients, influenza infection can lead to exacerbations resulting in reduced quality of life, hospitalization and death in the most severe cases. Although there is only limited literature on the use of influenza vaccination solely in COPD patients, there is clearly enough evidence to recommend annual vaccination in this group. This review will focus on influenza virus and prophylaxis with inactivated influenza vaccines in COPD patients and other “at risk” groups to reduce morbidity, save lives, and reduce health care costs.     

Now and future influenza vaccines

Influenza is a modern day plague. In the young, the clinical picture is classical, but in the elderly, the disease may go unsuspected until complications such as pneumonia develop. Influenza A and B viruses are responsible, and these viruses mutate with great regularity. Antibodies to the HA and NA surface antigens of influenza viruses, both naturally and vaccine induced, are protective. The earliest influenza vaccines were crude, toxic, and ineffective. With modern purification techniques, the egg-grown viruses have been turned into safe, immunogenic, and effective killed-virus vaccines--whole virus and split virus. Surveillance permits the correct virus strains to be incorporated into each new vaccine. Those who have been experiencing the worst effects of influenza have been identified. These individuals need to be immunized each year. In the future, live influenza virus vaccines may offer the benefits of ease of administration and longer-lasting protection. Synthetic peptides, genetically engineered antigens, and even nonantigen (anti-idiotype) vaccines are possible, but such vaccines will require adjuvant enhancement. For the present, greater efforts must be made to use existing influenza vaccines.