Cell culture-derived flu vaccine: Present and future

Insect-specific virus platforms for arbovirus vaccine development

Certain insect-specific viruses (ISVs), specifically the mosquito alphaviruses, Eilat and Yada Yada viruses, and orthoflaviviruses, Binjari, Aripo, YN15-283-02 and Chaoyang viruses, have emerged as potential platforms for generation of whole virus vaccines for human and veterinary applications. These ISVs are remarkably tolerant of the substitution of their structural polyproteins with those of alphaviruses and orthoflaviviruses that are pathogenic in humans and/or animals. The resulting ISV-based chimeric vaccines have been evaluated in mouse models and have demonstrated safety and efficacy in non-human primates, crocodiles and pigs. Targets include chikungunya, Venezuelan and eastern equine encephalitis, dengue, Zika, yellow fever, Japanese encephalitis and West Nile viruses. ISV-based chimeric vaccines provide authentically folded tertiary and quaternary whole virion particle structures to the immune system, a key feature for induction of protective antibody responses. These vaccines are manufactured in C6/36 or C7-10 mosquito cell lines, where they grow to high titers, but they do not replicate in vertebrate vaccine recipients. This review discusses the progress of these emerging technologies and addresses challenges related to adjuvanting, safety, and manufacturing.

Preventing Influenza Virus Infection and Severe Influenza Among Pregnant People and Infants

The landscape of research on the benefits of influenza vaccines and antivirals to protect pregnant persons and infants has increased in recent years, while influenza vaccination rates and antiviral usage have declined. Pregnant people and infants <6 months of age are at increased risk of hospitalization with influenza, making protection of this population essential. Maternal influenza vaccination at any time during pregnancy is the best way to reduce the risk of influenza and severe influenza in both pregnant people and their infants <6 months of age. Influenza antiviral medications for pregnant people and infants are also recommended as early as possible if influenza is confirmed or suspected. This report will update on the current research on the benefits of influenza vaccination during pregnancy and influenza antiviral medication for the pregnant person and infant, current Advisory Committee on Immunization Practices recommendations for influenza vaccination in pregnancy and vaccination coverage rates, current influenza antiviral medication guidance and usage rates in pregnancy and among infants, and future directions for influenza pregnancy research. With over half a century of maternal influenza vaccination in the United States, we have improved protection for pregnant persons and infants against influenza, but we still have room for improvement and optimization with new challenges to overcome following the COVID-19 pandemic. By continuing to fill research gaps and increase vaccination coverage and antiviral usage, there is potential for significant reductions in the domestic and global burden of influenza in pregnant persons and infants.

Protein Expression Platforms and the Challenges of Viral Antigen Production

Several protein expression platforms exist for a wide variety of biopharmaceutical needs. A substantial proportion of research and development into protein expression platforms and their optimization since the mid-1900s is a result of the production of viral antigens for use in subunit vaccine research. This review discusses the seven most popular forms of expression systems used in the past decade-bacterial, insect, mammalian, yeast, algal, plant and cell-free systems-in terms of advantages, uses and limitations for viral antigen production in the context of subunit vaccine research. Post-translational modifications, immunogenicity, efficacy, complexity, scalability and the cost of production are major points discussed. Examples of licenced and experimental vaccines are included along with images which summarize the processes involved.

Evaluation of the cross-protection of the Vero cell-derived attenuated influenza vaccines with compound adjuvant, through intranasal immunization

This study was to evaluate the sufficient safety and effect of the novel influenza vaccine program. It prepared new reassortant influenza virus, with high yield on Vero cells. According to the plaque counting, one dose LAIV was composed with 105 PFU of H1, H3, BY, and BV, respectively. Then mixed this LAIV with compound adjuvant, containing 500 μg/mL of carbopol971P and 50 μg/mL of tetanus toxin. That vaccination was called catt-flu. And it employed the GYZZ02 vaccine (commercialized freeze-dried LAIV, listed in China) as cohort analysis control. All mice received two doses of the vaccine, administered on days 0 and 14, respectively. That catt-flu program could induce more cross-protection with neutralizing antibody against heterogeneous types of influenza virus, not only based on HA but also NA protective antigen, through convenient nasal immunization, which had non-inferiority titter compared with the chicken embryo-derived GYZZ02 vaccine on safe and effect. The Vero cell-derived vaccine (LAIV) combined compound catt adjuvant (contain carbopol971P and tetanus toxin) could provide another safety and protective program of influenza vaccine by intranasal administration, as catt-flu program.

Production, Passaging Stability, and Histological Analysis of Madin-Darby Canine Kidney Cells Cultured in a Low-Serum Medium

Madin-Darby canine kidney (MDCK) cells are commonly used to produce cell-based influenza vaccines. However, the role of the low-serum medium on the proliferation of MDCK cells and the propagation of the influenza virus has not been well studied. In the present study, we used 5 of 15 culture methods with different concentrations of a mixed medium and neonatal bovine serum (NBS) to determine the best culture medium. We found that a VP:M199 ratio of 1:2 (3% NBS) was suitable for culturing MDCK cells. Furthermore, the stable growth of MDCK cells and the production of the influenza virus were evaluated over long-term passaging. We found no significant difference in terms of cell growth and virus production between high and low passages of MDCK cells under low-serum culture conditions, regardless of influenza virus infection. Lastly, we performed a comparison of the transcriptomics and proteomics of MDCK cells cultured in VP:M199 = 1:2 (3% NBS) with those cultured in VP:M199 = 1:2 (5% NBS) before and after influenza virus infection. The transcriptome analysis showed that differentially expressed genes were predominantly enriched in the metabolic pathway and MAPK signaling pathway, indicating an activated state. This suggests that decreasing the concentration of serum in the medium from 5% to 3% may increase the metabolic activity of cells. Proteomics analysis showed that only a small number of differentially expressed proteins could not be enriched for analysis, indicating minimal difference in the protein levels of MDCK cells when the serum concentration in the medium was decreased from 5% to 3%. Altogether, our findings suggest that the screening and application of a low-serum medium provide a background for the development and optimization of cell-based influenza vaccines.

Adjuvanted nanoliposomes displaying six hemagglutinins and neuraminidases as an influenza virus vaccine

Inclusion of defined quantities of the two major surface proteins of influenza virus, hemagglutinin (HA) and neuraminidase (NA), could benefit seasonal influenza vaccines. Recombinant HA and NA multimeric proteins derived from three influenza serotypes, H1N1, H3N2, and type B, are surface displayed on nanoliposomes co-loaded with immunostimulatory adjuvants, generating "hexaplex" particles that are used to immunize mice. Protective immune responses to hexaplex liposomes involve functional antibody elicitation against each included antigen, comparable to vaccination with monovalent antigen particles. When compared to contemporary recombinant or adjuvanted influenza virus vaccines, hexaplex liposomes perform favorably in many areas, including antibody production, T cell activation, protection from lethal virus challenge, and protection following passive sera transfer. Based on these results, hexaplex liposomes warrant further investigation as an adjuvanted recombinant influenza vaccine formulation.

Synthetic Cell Lines for Inducible Packaging of Influenza A Virus

Influenza A virus (IAV) is a negative-sense RNA virus that causes seasonal infections and periodic pandemics, inflicting huge economic and human costs on society. The current production of influenza virus for vaccines is initiated by generating a seed virus through the transfection of multiple plasmids in HEK293 cells followed by the infection of seed viruses into embryonated chicken eggs or cultured mammalian cells. We took a system design and synthetic biology approach to engineer cell lines that can be induced to produce all viral components except hemagglutinin (HA) and neuraminidase (NA), which are the antigens that specify the variants of IAV. Upon the transfection of HA and NA, the cell line can produce infectious IAV particles. RNA-Seq transcriptome analysis revealed inefficient synthesis of viral RNA and upregulated expression of genes involved in host response to viral infection as potential limiting factors and offered possible targets for enhancing the productivity of the synthetic cell line. Overall, we showed for the first time that it was possible to create packaging cell lines for the production of a cytopathic negative-sense RNA virus. The approach allows for the exploitation of altered kinetics of the synthesis of viral components and offers a new method for manufacturing viral vaccines.

The Screening and Mechanism of Influenza-Virus Sensitive MDCK Cell Lines for Influenza Vaccine Production

Influenza is a potentially fatal acute respiratory viral disease caused by the influenza virus. Influenza viruses vary in antigenicity and spread rapidly, resulting in seasonal epidemics. Vaccination is the most effective strategy for lowering the incidence and fatality rates of influenza-related disorders, and it is also an important method for reducing seasonal influenza infections. Mammalian Madin-Darby canine kidney (MDCK) cell lines are recommended for influenza virus growth, and such cell lines have been utilized in several commercial influenza vaccine productions. The limit dilution approach was used to screen ATCC-MDCK cell line subcellular strains that are especially sensitive to H1N1, H3N2, BV, and BY influenza viruses to increase virus production, and research on influenza virus culture media was performed to support influenza virus vaccine development. We also used RNA sequencing to identify differentially expressed genes and a GSEA analysis to determine the biological mechanisms underlying the various levels of susceptibility of cells to influenza viruses. MDCK cell subline 2B6 can be cultured to increase titer and the production of the H1N1, H3N2, BV, and BY influenza viruses. MDCK-2B6 has a significantly enriched and activated in ECM receptor interaction, JAK-STAT signaling, and cytokine receptor interaction signaling pathways, which may result in increased cellular susceptibility and cell proliferation activity to influenza viruses, promote viral adsorption and replication, and elevate viral production, ultimately. The study revealed that MDCK-2B6 can increase the influenza virus titer and yield in vaccine production by increasing cell sensitivity and enhancing proliferative activity.

Targeting neuraminidase: the next frontier for broadly protective influenza vaccines

Current seasonal influenza vaccines, which mainly target hemagglutinin (HA), require annual updates due to the continuous antigenic drift of the influenza virus. Developing an influenza vaccine with increased breadth of protection will have significant public health benefits. The recent discovery of broadly protective antibodies to neuraminidase (NA) has provided important insights into developing a universal influenza vaccine, either by improving seasonal influenza vaccines or designing novel immunogens. However, further in-depth molecular characterizations of NA antibody responses are warranted to fully leverage broadly protective NA antibodies for influenza vaccine designs. Overall, we posit that focusing on NA for influenza vaccine development is synergistic with existing efforts targeting HA, and may represent a cost-effective approach to generating a broadly protective influenza vaccine.

Overview of Avian Sex Reversal

Sex determination and differentiation are processes by which a bipotential gonad adopts either a testicular or ovarian cell fate, and secondary sexual characteristics adopt either male or female developmental patterns. In birds, although genetic factors control the sex determination program, sex differentiation is sensitive to hormones, which can induce sex reversal when disturbed. Although these sex-reversed birds can form phenotypes opposite to their genotypes, none can experience complete sex reversal or produce offspring under natural conditions. Promising evidence indicates that the incomplete sex reversal is associated with cell autonomous sex identity (CASI) of avian cells, which is controlled by genetic factors. However, studies cannot clearly describe the regulatory mechanism of avian CASI and sex development at present, and these factors require further exploration. In spite of this, the abundant findings of avian sex research have provided theoretical bases for the progress of gender control technologies, which are being improved through interdisciplinary co-operation and will ultimately be employed in poultry production. In this review, we provide an overview of avian sex determination and differentiation and comprehensively summarize the research progress on sex reversal in birds, especially chickens. Importantly, we describe key issues faced by applying gender control systems in poultry production and chronologically summarize the development of avian sex control methods. In conclusion, this review provides unique perspectives for avian sex studies and helps scientists develop more advanced systems for sex regulation in birds.

CpG dinucleotide enrichment in the influenza A virus genome as a live attenuated vaccine development strategy

Synonymous recoding of RNA virus genomes is a promising approach for generating attenuated viruses to use as vaccines. Problematically, recoding typically hinders virus growth, but this may be rectified using CpG dinucleotide enrichment. CpGs are recognised by cellular zinc-finger antiviral protein (ZAP), and so in principle, removing ZAP sensing from a virus propagation system will reverse attenuation of a CpG-enriched virus, enabling high titre yield of a vaccine virus. We tested this using a vaccine strain of influenza A virus (IAV) engineered for increased CpG content in genome segment 1. Virus attenuation was mediated by the short isoform of ZAP, correlated with the number of CpGs added, and was enacted via turnover of viral transcripts. The CpG-enriched virus was strongly attenuated in mice, yet conveyed protection from a potentially lethal challenge dose of wildtype virus. Importantly for vaccine development, CpG-enriched viruses were genetically stable during serial passage. Unexpectedly, in both MDCK cells and embryonated hens' eggs that are used to propagate live attenuated influenza vaccines, the ZAP-sensitive virus was fully replication competent. Thus, ZAP-sensitive CpG enriched viruses that are defective in human systems can yield high titre in vaccine propagation systems, providing a realistic, economically viable platform to augment existing live attenuated vaccines.

Hemagglutinin destabilization in H3N2 vaccine reference viruses skews antigenicity and prevents airborne transmission in ferrets

During influenza virus entry, the hemagglutinin (HA) protein binds receptors and causes membrane fusion after endosomal acid activation. To improve vaccine efficiency and pandemic risk assessment for currently-dominant H3N2 influenza viruses, we investigated HA stability of 6 vaccine reference viruses and 42 circulating viruses. Recent vaccine reference viruses had destabilized HA proteins due to egg-adaptive mutation HA1-L194P. Virus growth in cell culture was independent of HA stability. In ferrets, the vaccine reference viruses and circulating viruses required a relatively stable HA (activation and inactivation pH < 5.5) for airborne transmissibility. The recent vaccine reference viruses with destabilized HA proteins had reduced infectivity, had no airborne transmissibility unless reversion to HA1-P194L occurred, and had skewed antigenicity away from the studied viruses and circulating H3N2 viruses. Other vaccine reference viruses with stabilized HAs retained infectivity, transmissibility, and antigenicity. Therefore, HA stabilization should be prioritized over destabilization in vaccine reference virus selection to reduce mismatches between vaccine and circulating viruses.

Post-marketing surveillance study on influenza vaccine in South Korea using a nationwide spontaneous reporting database with multiple data mining methods

Safety profiles of the influenza vaccine and its subtypes are still limited. We aimed to address this knowledge gap using multiple data mining methods and calculated performance measurements to evaluate the precision of different detection methods. We conducted a post-marketing surveillance study between 2005 and 2019 using the Korea Adverse Event Reporting System database. Three data mining methods were applied: (a) proportional reporting ratio, (b) information component, and (c) tree-based scan statistics. We evaluated the performance of each method in comparison with the known adverse events (AEs) described in the labeling information. Compared to other vaccines, we identified 36 safety signals for the influenza vaccine, and 7 safety signals were unlabeled. In subtype-stratified analyses, application site disorders were reported more frequently with quadrivalent and cell-based vaccines, while a wide range of AEs were noted for trivalent and egg-based vaccines. Tree-based scan statistics showed well-balanced performance. Among the detected signals of influenza vaccines, narcolepsy requires special attention. A wider range of AEs were detected as signals for trivalent and egg-based vaccines. Although tree-based scan statistics showed balanced performance, complementary use of other techniques would be beneficial when large noise due to false positives is expected.

The Epidemiology of Influenza and the Associated Vaccines Development in China: A Review

Influenza prevention and control has been one of the biggest challenges encountered in the public health domain. The vaccination against influenza plays a pivotal role in the prevention of influenza, particularly for the elderly and small children. According to the epidemiology of influenza in China, the nation is under a heavy burden of this disease. Therefore, as a contribution to the prevention and control of influenza in China through the provision of relevant information, the present report discusses the production and batch issuance of the influenza vaccine, analysis of the vaccination status and vaccination rate of the influenza vaccine, and the development trend of the influenza vaccine in China.

Preclinical immunogenicity assessment of a cell-based inactivated whole-virion H5N1 influenza vaccine

In influenza vaccine development, Madin–Darby canine kidney (MDCK) cells provide multiple advantages, including large-scale production and egg independence. Several cell-based influenza vaccines have been approved worldwide. We cultured H5N1 virus in a serum-free MDCK cell suspension. The harvested virus was manufactured into vaccines after inactivation and purification. The vaccine effectiveness was assessed in the Wuhan Institute of Biological Products BSL2 facility. The pre- and postvaccination mouse serum titers were determined using the microneutralization and hemagglutination inhibition tests. The immunological responses induced by vaccine were investigated using immunological cell classification, cytokine expression quantification, and immunoglobulin G (IgG) subtype classification. The protective effect of the vaccine in mice was evaluated using challenge test. Antibodies against H5N1 in rats lasted up to 8 months after the first dose. Compared with those of the placebo group, the serum titer of vaccinated mice increased significantly, Th1 and Th2 cells were activated, and CD8+ T cells were activated in two dose groups. Furthermore, the challenge test showed that vaccination reduced the clinical symptoms and virus titer in the lungs of mice after challenge, indicating a superior immunological response. Notably, early after vaccination, considerably increased interferon-inducible protein-10 (IP-10) levels were found, indicating improved vaccine-induced innate immunity. However, IP-10 is an adverse event marker, which is a cause for concern. Overall, in the case of an outbreak, the whole-virion H5N1 vaccine should provide protection.

Controlled Human Infection Models To Accelerate Vaccine Development

The timelines for developing vaccines against infectious diseases are lengthy, and often vaccines that reach the stage of large phase 3 field trials fail to provide the desired level of protective efficacy. The application of controlled human challenge models of infection and disease at the appropriate stages of development could accelerate development of candidate vaccines and, in fact, has done so successfully in some limited cases. Human challenge models could potentially be used to gather critical information on pathogenesis, inform strain selection for vaccines, explore cross-protective immunity, identify immune correlates of protection and mechanisms of protection induced by infection or evoked by candidate vaccines, guide decisions on appropriate trial endpoints, and evaluate vaccine efficacy. We prepared this report to motivate fellow scientists to exploit the potential capacity of controlled human challenge experiments to advance vaccine development. In this review, we considered available challenge models for 17 infectious diseases in the context of the public health importance of each disease, the diversity and pathogenesis of the causative organisms, the vaccine candidates under development, and each model's capacity to evaluate them and identify correlates of protective immunity. Our broad assessment indicated that human challenge models have not yet reached their full potential to support the development of vaccines against infectious diseases. On the basis of our review, however, we believe that describing an ideal challenge model is possible, as is further developing existing and future challenge models.

Development of low-cost cage-like particles to formulate veterinary vaccines

Low-cost adjuvants are urgently needed for the development of veterinary vaccines able to trigger strong immune responses. In this work, we describe a method to obtain a low-cost cage-like particles (ISCOMATRIX-like) adjuvant useful to formulate veterinary vaccines candidates. The main components to form the particles are lipids and saponins, which were obtained from egg yolk by ethanolic extraction and by dialyzing a non-refined saponins extract, respectively. Lipids were fully characterized by thin layer chromatography (TLC) and gas-chromatography (GC) and enzymatic methods, and saponins were characterized by TLC, HPLC and MALDI-TOF. Cage-like particles were prepared with these components or with commercial inputs. Both particles and the traditional Alum used in veterinary vaccines were compared by immunizing mice with Ovalbumin (OVA) formulated with these adjuvants and assessing IgG1, IgG2a anti OVA antibodies and specific Delayed-type Hypersensitivity (DTH). In the yolk extract, a mixture of phospholipids, cholesterol and minor components of the extract (e.g. lyso-phospholipids) with suitable proportions to generate cage-like particles was obtained. Also, semi-purified saponins with similar features to those of the QuilA® were obtained. Cage-like particles prepared with these components have 40-50 nm and triggers similar levels of Anti-OVA IgG1 and DTH than with commercial inputs but higher specific-IgG2a. Both adjuvants largely increased the levels of IgG1, IgG2a and DTH in relation to the formulation with Alum. The methods described to extract lipids from egg yolk and saponins from non-refined extract allowed us to obtain an inexpensive and highly effective adjuvant.

Generation of a live attenuated influenza A vaccine by proteolysis targeting

The usefulness of live attenuated virus vaccines has been limited by suboptimal immunogenicity, safety concerns or cumbersome manufacturing processes and techniques. Here we describe the generation of a live attenuated influenza A virus vaccine using proteolysis-targeting chimeric (PROTAC) technology to degrade viral proteins via the endogenous ubiquitin-proteasome system of host cells. We engineered the genome of influenza A viruses in stable cell lines engineered for virus production to introduce a conditionally removable proteasome-targeting domain, generating fully infective PROTAC viruses that were live attenuated by the host protein degradation machinery upon infection. In mouse and ferret models, PROTAC viruses were highly attenuated and able to elicit robust and broad humoral, mucosal and cellular immunity against homologous and heterologous virus challenges. PROTAC-mediated attenuation of viruses may be broadly applicable for generating live attenuated vaccines.

Systematic review of the efficacy, effectiveness and safety of cell-based seasonal influenza vaccines for the prevention of laboratory-confirmed influenza in individuals ≥18 years of age

The most effective means of preventing seasonal influenza is through strain-specific vaccination. In this study, we investigated the efficacy, effectiveness and safety of cell-based trivalent and quadrivalent influenza vaccines. A systematic literature search was conducted in electronic databases and grey literature sources up to 7 February 2020. Randomised controlled trials (RCTs) and non-randomised studies of interventions (NRSIs) were eligible for inclusion. Two reviewers independently screened, extracted data and assessed the risk of bias of included studies. Certainty of evidence for key outcomes was assessed using the GRADE methodology. The search returned 28,846 records, of which 868 full-text articles were assessed for relevance. Of these, 19 studies met the inclusion criteria. No relative efficacy data were identified for the direct comparison of cell-based vaccines compared with traditional vaccines (egg-based). Efficacy data were available comparing cell-based trivalent influenza vaccines with placebo in adults (aged 18-49 years). Overall vaccine efficacy was 70% against any influenza subtype (95% CI 61%-77%, two RCTS), 82% against influenza A(H1N1) (95% CI 71%-89%, 2 RCTs), 72% against influenza A(H3N2) (95% CI 39%-87%, 2 RCTs) and 52% against influenza B (95% CI 30%-68%, 2 RCTs). Limited and heterogeneous data were presented for effectiveness when compared with no vaccination. One NRSI compared cell-based trivalent and quadrivalent vaccination with traditional trivalent and quadrivalent vaccination, finding a small but significant difference in favour of cell-based vaccines for influenza-related hospitalisation, hospital encounters and physician office visits. The safety profile of cell-based trivalent vaccines was comparable to traditional trivalent influenza vaccines. Compared with placebo, cell-based trivalent influenza vaccines have demonstrated greater efficacy in adults aged 18-49 years. Overall cell-based vaccines are well-tolerated in adults, however, evidence regarding the effectiveness of these vaccines compared with traditional seasonal influenza vaccines is limited.

The Highly Productive Thermothelomyces heterothallica C1 Expression System as a Host for Rapid Development of Influenza Vaccines

(1) Influenza viruses constantly change and evade prior immune responses, forcing seasonal re-vaccinations with updated vaccines. Current FDA-approved vaccine manufacturing technologies are too slow and/or expensive to quickly adapt to mid-season changes in the virus or to the emergence of pandemic strains. Therefore, cost-effective vaccine technologies that can quickly adapt to newly emerged strains are desirable. (2) The filamentous fungal host Thermothelomyces heterothallica C1 (C1, formerly Myceliophthora thermophila) offers a highly efficient and cost-effective alternative to reliably produce immunogens of vaccine quality at large scale. (3) We showed the utility of the C1 system expressing hemagglutinin (HA) and a HA fusion protein from different H1N1 influenza A virus strains. Mice vaccinated with the C1-derived HA proteins elicited anti-HA immune responses similar, or stronger than mice vaccinated with HA products derived from prototypical expression systems. A challenge study demonstrated that vaccinated mice were protected against the aggressive homologous viral challenge. (4) The C1 expression system is proposed as part of a set of protein expression systems for plug-and-play vaccine manufacturing platforms. Upon the emergence of pathogens of concern these platforms could serve as a quick solution for producing enough vaccines for immunizing the world population in a much shorter time and more affordably than is possible with current platforms.

Subtype H3N2 Influenza A Viruses: An Unmet Challenge in the Western Pacific

Subtype H3N2 influenza A viruses (A(H3N2)) have been the dominant strain in some countries in the Western Pacific region since the 2009 influenza A(H1N1) pandemic. Vaccination is the most effective way to prevent influenza; however, low vaccine effectiveness has been reported in some influenza seasons, especially for A(H3N2). Antigenic mismatch introduced by egg-adaptation during vaccine production between the vaccine and circulating viral stains is one of the reasons for low vaccine effectiveness. Here we review the extent of this phenomenon, the underlying molecular mechanisms and discuss recent strategies to ameliorate this, including new vaccine platforms that may provide better protection and should be considered to reduce the impact of A(H3N2) in the Western Pacific region.

Influenza Vaccine: An Engineering Vision from Virological Importance to Production

According to data from the World Health Organization (WHO) every year, millions of people are affected by flu. Flu is a disease caused by influenza viruses. For preventing this, seasonal influenza vaccinations are widely considered the most efficient way to protect against the negative effects of the flu. To date, there is no "one-size-fits-all" vaccine that can be effective all over the world to protect against all seasonal or pandemic influenza virus types. Because influenza virus transforms its genetic structure and it can emerges as immunogenically new (antigenic drift) which causes epidemics or new virus subtype (antigenic shift) which causes pandemics. As a result, annual revaccination or new subtype viral vaccine development is required. Currently, three types of vaccines (inactivated, live attenuated, and recombinant) are approved in different countries. These can be named "conventional influenza vaccines" and their production are based on eggs or cell culture. Although, there is good effort to develop new influenza vaccines for broader and longer period of time protection. In this sense these candidate vaccines are called "universal influenza vaccines". In this article, after we mentioned the short history of flu then virus morphology and infection, we explained the diseases caused by the influenza virus in humans. Afterward, we explained in detail the production methods of available influenza vaccines, types of bioreactors used in cell culture based production, conventional and new vaccine types, and development strategies for better vaccines.

Estimation of Reduction in Influenza Vaccine Effectiveness Due to Egg-Adaptation Changes-Systematic Literature Review and Expert Consensus

BACKGROUND

Influenza vaccines are the main tool to prevent morbidity and mortality of the disease; however, egg adaptations associated with the choice of the manufacturing process may reduce their effectiveness. This study aimed to estimate the impact of egg adaptations and antigenic drift on the effectiveness of trivalent (TIV) and quadrivalent (QIV) influenza vaccines.

METHODS

Nine experts in influenza virology were recruited into a Delphi-style exercise. In the first round, the experts were asked to answer questions on the impact of antigenic drift and egg adaptations on vaccine match (VM) and influenza vaccine effectiveness (IVE). In the second round, the experts were presented with the data from a systematic literature review on the same subject and aggregated experts' responses to round one questions. The experts were asked to review and confirm or amend their responses before the final summary statistics were calculated.

RESULTS

The experts estimated that, across Europe, the egg adaptations reduce, on average, VM to circulating viruses by 7-21% and reduce IVE by 4-16%. According to the experts, antigenic drift results in a similar impact on VM (8-24%) and IVE (5-20%). The highest reduction in IVE was estimated for the influenza virus A(H3N2) subtype for the under 65 age group. When asked about the frequency of the phenomena, the experts indicated that, on average, between the 2014 and 19 seasons, egg adaptation and antigenic drift were significant enough to impact IVE that occurred in two and three out of five seasons, respectively. They also agreed that this pattern is likely to reoccur in future seasons.

CONCLUSIONS

Expert estimates suggest there is a potential for 9% on average (weighted average of "All strains" over three age groups adjusted by population size) and up to a 16% increase in IVE (against A(H3N2), the <65 age group) if egg adaptations that arise when employing the traditional egg-based manufacturing process are avoided.

Evaluation of the antigenic stability of influenza virus like particles after exposure to acidic or basic pH

Purpose

Virus-like particles (VLPs) are being developed as a promising vaccine platform and therapeutic delivery. Various strategies for effectively constructing VLPs have been studied, but relatively few studies have been done on various factors affecting storage. In this study, we investigated the antigenic changes of VLPs in an acidic or basic pH environment using influenza VLPs as an experimental model.

Materials and Methods

Influenza VLPs containing hemagglutination and M1 proteins were generated and their antigenicity and protective immunity in vitro and in vivo were evaluated after exposure to acidic (pH 4 and 5) or basic (pH 9 and 10) pH buffers.

Results

VLP exposed to basic pH showed similar levels of antigenicity to those stored in neutral pH, while antigenicity of VLP exposed to acidic pH was found to be significantly reduced compared to those expose neutral or basic pH. All groups of mice responded effectively to low concentrations of virus infections; however, VLP vaccine groups exposed to acid pH were found not to induce sufficient protective immune responses when a high concentration of influenza virus infection.

Conclusion

In order for VLP to be used as a more powerful vaccine platform, it should be developed in a strategic way to respond well to external changes such as acidic pH conditions.

Approaches in broadening the neutralizing antibody response of the influenza vaccine

INTRODUCTION

Influenza vaccine is the mainstay for influenza prevention and elicits immune response and antigen-specific neutralizing antibodies against influenza virus. However, antigenic drift and shift can confer influenza virus to escape from the immune response induced by vaccine, and then reduce the vaccine effectiveness.

AREAS COVERED

To improve effect and neutralizing antibody response of vaccine for heterologous influenza virus, a literature review of preclinical and clinical studies published before August 2021 and searched in PubMed, which evaluated vaccine effectiveness improved by adjuvants and administration route.

EXPERT OPINION

The review showed that adjuvant, including imiquimod, GLA, MF59, and AS03, can improve the effectiveness of influenza vaccines by regulating immune system. Subjects receiving influenza vaccine combined with these adjuvants showed enhanced antibody response against homologous and heterologous virus strains compared to those vaccinated without adjuvant. This review also discussed the role of intradermal vaccination. In contrast to intramuscular vaccination, intradermal vaccination elicited a robust and prolonged antibody response against vaccine strains and drifted virus than intramuscular vaccination.

[Vaccination against community acquired pneumonia in adults. Update 2021 of the position paper by Neumoexpertos en Prevención Group]

Community-acquired pneumonia (CAP) continues to be an important cause of morbidity and mortality in adults. The aim of this study is to update the practical prevention guide for CAP through vaccination in Spain developed in 2016 and updated in 2018, based on available vaccines and evidence through bibliographic review and expert opinion. The arrival of COVID-19 as a new cause of CAP and the recent availability of safe and effective vaccines constitutes the most significant change. Vaccines against pneumococcus, influenza, pertussis and COVID-19 can help to reduce the burden of disease from CAP and its associated complications. The available evidence supports the priority indications established in this guide, and it would be advisable to try to achieve a widespread dissemination and implementation of these recommendations in routine clinical practice.

Comparison of N-linked glycosylation on hemagglutinins derived from chicken embryos and MDCK cells: a case of the production of a trivalent seasonal influenza vaccine

Abstract

N-linked glycosylation plays critical roles in folding, receptor binding, and immunomodulating of hemagglutinin (HA), the main antigen in influenza vaccines. Chicken embryos are the predominant production host for influenza vaccines, but Madin-Darby canine kidney (MDCK) cells have emerged as an important alternative host. In this study, we compared glycosylation patterns, including the occupancy of potential glycosylation sites and the distribution of different glycans, on the HAs of three strains of influenza viruses for the production a trivalent seasonal flu vaccine for the 2015-2016 Northern Hemisphere season (i.e., A/California/7/2009 (H1N1) X179A, A/Switzerland/9715293/2013 (H3N2) NIB-88, and B/Brisbane/60/2008 NYMC BX-35###). Of the 8, 12, and 11 potential glycosylation sites on the HAs of H1N1, H3N2, and B strains, respectively, most were highly occupied. For the H3N2 and B strains, MDCK-derived HAs contained more sites being partially occupied (<95%) than embryo-derived HAs. A highly sensitive glycan assay was developed where 50 different glycans were identified, which was more than what has been reported previously, and their relative abundance was quantified. In general, MDCK-derived HAs contain more glycans of higher molecular weight. High-mannose species account for the most abundant group of glycans, but at a lower level as compared to those reported in previous studies, presumably due to that lower abundance, complex structure glycans were accounted for in this study. The different glycosylation patterns between MDCK- and chicken embryo-derived HAs may help elucidate the role of glycosylation on the function of influenza vaccines.

Key points

• For the H3N2 and B strains, MDCK-derived HAs contained more partially (<95%) occupied glycosylation sites.

• MDCK-derived HAs contained more glycans of higher molecular weight.

• A systematic comparison of glycosylation on HAs used for trivalent seasonal flu vaccines was conducted.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00253-021-11247-5.

Flow virometry for process monitoring of live virus vaccines-lessons learned from ERVEBO

Direct at line monitoring of live virus particles in commercial manufacturing of vaccines is challenging due to their small size. Detection of malformed or damaged virions with reduced potency is rate-limited by release potency assays with long turnaround times. Thus, preempting batch failures caused by out of specification potency results is almost impossible. Much needed are in-process tools that can monitor and detect compromised viral particles in live-virus vaccines (LVVs) manufacturing based on changes in their biophysical properties to provide timely measures to rectify process stresses leading to such damage. Using ERVEBO, MSD's Ebola virus vaccine as an example, here we describe a flow virometry assay that can quickly detect damaged virus particles and provide mechanistic insight into process parameters contributing to the damage. Furthermore, we describe a 24-h high throughput infectivity assay that can be used to correlate damaged particles directly to loss in viral infectivity (potency) in-process. Collectively, we provide a set of innovative tools to enable rapid process development, process monitoring, and control strategy implementation in large scale LVV manufacturing.

Virucidal activity of Moringa A from Moringa oleifera seeds against Influenza A Viruses by regulating TFEB

Influenza A viruses (IAVs) are highly contagious pathogens infecting human and numerous animals. The viruses cause millions of infection cases and thousands of deaths every year, making IAVs a continual threat to global health. Our study demonstrated the virucidal activity of Moringa A as a new compound from Moringa oleifera seeds against IAVs. It inhibits virus replication in host cells and protects infected cells from the cytopathic effect induced by IAVs. The EC50andEC90 values of Moringa A for IAVs were 1.27 and 5.30 μM, respectively, when RAW264.7 cells were infected at MOI of 1. The different treatment experiments revealed that Moringa A has a significant inhibitory effect on the IAVs both before and afterdrug addition. Moringa A was observed to decrease the inflammatory cytokines TNF-α, IL-6, IL-1β, and IFN-β in H1N1 infected RAW264.7 cells. Finally, Moringa A was found to inhibit the expression and nuclear transfer of the cellular protein transcription factor EB (TFEB) and weaken the autophagy in infected cells, which could be an important antiviral mechanism. Our study demonstrates Moringa A has potent antiviral activity against IVAs, which could be due to the autophagy inhibition property.

New Vaccine-Manufacturing Methods Are Moving Away From the Egg

With seasonal influenza, Ebola, shingles, pneumonia, human papillomavirus, and other pathogens-combined now with the novel coronavirus (SARS-CoV-2)-the world's demand for vaccines is on a steep incline. New vaccine development is progressing rapidly, as seen with recent announcements of coronavirus options [1], [2], but what about their manufacture?

Evaluation of manufacturing feasibility and safety of an MDCK cell-based live attenuated influenza vaccine (LAIV) platform

Cell culture based live attenuated influenza vaccines (LAIV) as an alternative to egg-based LAIV have been explored because of lack of easy access to SPF eggs for large scale production. In this study, feasibility of MDCK platform was assessed by including multiple LAIV strains covering both type A (H1 and H3) and type B seasonal strains as well as the candidate pandemic potential strains like A/H5 and A/H7 for the growth in MDCK cells. A risk assessment study was conducted on the cell banks to evaluate safety concerns related to tumorigenicity with a regulatory perspective. Tumorigenic potential of the MDCK cells was evaluated in nude mice (10⁷cells/mouse) model system. The 50% tumor producing dose (TPD₅₀) of MDCK cells was studied in SCID mice to determine the amount of cells required for induction of tumors. Further, we conducted an oncogenicity study in three sensitive rodent species as per the requirements specified in the WHO guidelines. We determined TPD₅₀ value of 1.9 X 10⁴ cells/mice through subcutaneous route. Our results suggest that, the intranasal route of administration of the cell culture based LAIV pose minimal to no risk of tumorigenicity associated with the host cells. Also, non-oncogenic nature of MDCK cells was demonstrated. Host cell DNA in the vaccine formulations was < 10 ng/dose which ensures vaccine safety. Production efficiency and consistency were characterized and the observed titer values of the viral harvest and the processed bulk were comparable to the expansion in embryonated eggs. The present study clearly establishes the suitability of MDCK cells as a substrate for the manufacture of a safe and viable LAIV.

New Technologies for Influenza Vaccines

Vaccine development has been hampered by the long lead times and the high cost required to reach the market. The 2020 pandemic, caused by a new coronavirus (SARS-CoV-2) that was first reported in late 2019, has seen unprecedented rapid activity to generate a vaccine, which belies the traditional vaccine development cycle. Critically, much of this progress has been leveraged off existing technologies, many of which had their beginnings in influenza vaccine development. This commentary outlines the most promising of the next generation of non-egg-based influenza vaccines including new manufacturing platforms, structure-based antigen design/computational biology, protein-based vaccines including recombinant technologies, nanoparticles, gene- and vector-based technologies, as well as an update on activities around a universal influenza vaccine.

Development and Evaluation of Vero Cell-Derived Master Donor Viruses for Influenza Pandemic Preparedness

The embryonated egg-based platform currently produces the majority of seasonal influenza vaccines by employing a well-developed master donor virus (MDV, A/PR/8/34 (PR8)) to generate high-growth reassortants (HGRs) for A/H1N1 and A/H3N2 subtypes. Although the egg-based platform can supply enough seasonal influenza vaccines, it cannot meet surging demands during influenza pandemics. Therefore, multi-purpose platforms are desirable for pandemic preparedness. The Vero cell-based production platform is widely used for human vaccines and could be a potential multi-purpose platform for pandemic influenza vaccines. However, many wild-type and egg-derived influenza viruses cannot grow efficiently in Vero cells. Therefore, it is critical to develop Vero cell-derived high-growth MDVs for pandemic preparedness. In this study, we evaluated two in-house MDVs (Vero-15 and VB5) and two external MDVs (PR8 and PR8-HY) to generate Vero cell-derived HGRs for five avian influenza viruses (AIVs) with pandemic potentials (H5N1 clade 2.3.4, H5N1 clade 2.3.2.1, American-lineage H5N2, H7N9 first wave and H7N9 fifth wave). Overall, no single MDV could generate HGRs for all five AIVs, but this goal could be achieved by employing two in-house MDVs (vB5 and Vero-15). In immunization studies, mice received two doses of Vero cell-derived inactivated H5N1 and H7N9 whole virus antigens adjuvanted with alum and developed robust antibody responses.

Quadrivalent cell culture influenza virus vaccine. Comparison to egg-derived vaccine

Influenza virus infections pose a serious public health problem and vaccination is the most effective public health intervention against them. The current manufacture of influenza vaccines in embryonated chicken eggs entails significant limitations. These limitations have been overcome by producing vaccines in cell culture, which allow a faster and more flexible response to potential pandemic threats. Given the impact of influenza B virus on disease burden, the availability of quadrivalent vaccines is useful for increasing the rate of protection from disease. This paper analyzes the limitations of the current production of influenza vaccine in eggs and the advantages of vaccines developed in cell culture, as well as their safety, tolerability, efficacy and effectiveness. Additionally, we reflect on the contribution of new quadrivalent vaccines from cell culture as an alternative in seasonal vaccination campaigns against influenza.

Constrained Optimization for the Selection of Influenza Vaccines to Maximize the Population Benefit: A Demonstration Project

BACKGROUND

Influenza is an infectious disease causing a high annual economic and public health burden. The most efficient management of the disease is through prevention with vaccination. Many influenza vaccines are available, with varying efficacy and cost, targeting different age groups. Therefore, strategic decision-making about which vaccine to deliver to whom is warranted to improve efficiency.

OBJECTIVE

We present the use of a constrained optimization (CO) model to evaluate targeted strategies for providing influenza vaccines in three adult age groups in the USA.

METHODS

CO was considered for identifying an influenza vaccine provision strategy that maximizes the benefits at constrained annual budgets, by prioritizing vaccines based on return on investment. The approach optimizes a set of predefined outcome measures over several years resulting from an increasing investment using the best combination of influenza vaccines.

RESULTS

Results indicate the importance of understanding the relative differences in benefits for each vaccine type within and across age groups. Scenario and threshold analyses demonstrate the impact of changing budget distribution over time, price setting per vaccine type, and selection of outcome measure to optimize.

CONCLUSION

Significant gains in cost efficiency can be realized for a decision maker using a CO model, especially for a disease like influenza with many vaccine options. Testing the model under different scenarios offers powerful insights into maximum achievable benefit overall and per age group within the predefined constraints of a vaccine budget.

Influenza Virus Like Particles (VLPs): Opportunities for H7N9 Vaccine Development

In the midst of the ongoing COVID-19 coronavirus pandemic, influenza virus remains a major threat to public health due to its potential to cause epidemics and pandemics with significant human mortality. Cases of H7N9 human infections emerged in eastern China in 2013 and immediately raised pandemic concerns as historically, pandemics were caused by the introduction of new subtypes into immunologically naïve human populations. Highly pathogenic H7N9 cases with severe disease were reported recently, indicating the continuing public health threat and the need for a prophylactic vaccine. Here we review the development of recombinant influenza virus-like particles (VLPs) as vaccines against H7N9 virus. Several approaches to vaccine development are reviewed including the expression of VLPs in mammalian, plant and insect cell expression systems. Although considerable progress has been achieved, including demonstration of safety and immunogenicity of H7N9 VLPs in the human clinical trials, the remaining challenges need to be addressed. These challenges include improvements to the manufacturing processes, as well as enhancements to immunogenicity in order to elicit protective immunity to multiple variants and subtypes of influenza virus.

Next-generation influenza vaccines: opportunities and challenges

Seasonal influenza vaccines lack efficacy against drifted or pandemic influenza strains. Developing improved vaccines that elicit broader immunity remains a public health priority. Immune responses to current vaccines focus on the haemagglutinin head domain, whereas next-generation vaccines target less variable virus structures, including the haemagglutinin stem. Strategies employed to improve vaccine efficacy involve using structure-based design and nanoparticle display to optimize the antigenicity and immunogenicity of target antigens; increasing the antigen dose; using novel adjuvants; stimulating cellular immunity; and targeting other viral proteins, including neuraminidase, matrix protein 2 or nucleoprotein. Improved understanding of influenza antigen structure and immunobiology is advancing novel vaccine candidates into human trials.

Development of American-Lineage Influenza H5N2 Reassortant Vaccine Viruses for Pandemic Preparedness

Novel low-pathogenic avian influenza (LPAI) H5N2 viruses hit poultry farms in Taiwan in 2003, and evolved into highly pathogenic avian influenza (HPAI) viruses in 2010. These viruses are reassortant viruses containing HA and NA genes from American-lineage H5N2 and six internal genes from local H6N1 viruses. According to a serological survey, the Taiwan H5N2 viruses can cause asymptomatic infections in poultry workers. Therefore, a development of influenza H5N2 vaccines is desirable for pandemic preparation. In this study, we employed reverse genetics to generate a vaccine virus having HA and NA genes from A/Chicken/CY/A2628/2012 (E7, LPAI) and six internal genes from a Vero cell-adapted high-growth H5N1 vaccine virus (Vero-15). The reassortant H5N2 vaccine virus, E7-V15, presented high-growth efficiency in Vero cells (512 HAU, 10^7.6 TCID₅₀/mL), and passed all tests for qualification of candidate vaccine viruses. In ferret immunization, two doses of inactivated whole virus antigens (3 μg of HA protein) adjuvanted with alum could induce robust antibody response (HI titre 113.14). In conclusion, we have established reverse genetics to generate a qualified reassortant H5N2 vaccine virus for further development.

Evidence of Influenza A in Wild Norway Rats (Rattus norvegicus) in Boston, Massachusetts

Influenza A virus (IAV) is known to circulate among human and animal reservoirs, yet there are few studies that address the potential for urban rodents to carry and shed IAV. Rodents are often used as influenza models in the lab, but the few field studies that have looked for evidence of IAV in rodents have done so primarily in rural areas following outbreaks of IAV in poultry. This study sought to assess the prevalence of IAV recovered from wild Norway rats in a dense urban location (Boston). To do this, we sampled the oronasal cavity, paws, and lungs of Norway rats trapped by the City of Boston's Inspectional Services from December 2016 to September 2018. All samples were screened by real-time, reverse transcriptase PCR targeting the conserved IAV matrix segment. A total of 163 rats were trapped, 18 of which (11.04%) were RT-PCR positive for IAV in either oronasal swabs (9), paw swabs (9), both (2), or lung homogenates (2). A generalized linear model indicated that month and geographic location were correlated with IAV-positive PCR status of rats. A seasonal trend in IAV-PCR status was observed with the highest prevalence occurring in the winter months (December-January) followed by a decline over the course of the year, reaching its lowest prevalence in September. Sex and weight of rats were not significantly associated with IAV-PCR status, suggesting that rodent demography is not a primary driver of infection. This pilot study provides evidence of the need to further investigate the role that wild rats may play as reservoirs or mechanical vectors for IAV circulation in urban environments across seasons.

[Adult community acquired pneumonia vaccination: 2018 Update of the positioning of the Pneumonia Prevention Expert Group]

Community-acquired pneumonia (CAP) continues to be an important cause of morbidity and mortality in adults. The aim of this study is to update the 2016 practical prevention guidelines for CAP through vaccination in Spain, based on the available vaccines, as well as the evidence using a literature review and expert opinion. Vaccines against pneumococcus and influenza continue to be the main prevention tools available against CAP, and can contribute to reduce the burden of disease due to CAP and its associated complications. The available evidence supports the priority indications established in these guidelines, and it would be advisable to try to achieve a widespread dissemination and implementation of these recommendations in routine clinical practice.