Contemporary H3N2 influenza viruses have a glycosylation site that alters binding of antibodies elicited by egg-adapted vaccine strains

Modelling the Economic Impact of lnfluenza Vaccine Programs with the Cell-Based Quadrivalent Influenza Vaccine and Adjuvanted Trivalent Influenza Vaccine in Canada

In Canada, approximately 12,000 people annually are hospitalized with influenza. While vaccination is the most effective method for reducing the burden of seasonal influenza, the propagation of vaccine virus strains in eggs can result in egg adaption, resulting in reduced antigenic similarity to circulating strains and thus lower vaccine effectiveness (VE). Cell-based propagation methods avoid these alterations and therefore may be more effective than egg-propagation vaccines. We evaluated three different scenarios: (1) egg-based quadrivalent influenza vaccine (QIVe) for individuals <65 years and adjuvanted trivalent influenza vaccine (aTIV) for ≥65 years; (2) QIVe (<65 years) and high-dose QIV (HD −; QIV; ≥65 years); and (3) cell-based derived QIV (QIVc; <65 years) and aTIV (≥65 years) compared with a baseline scenario of QIVe for all age groups. Modelling was performed using a dynamic age-structured SEIR model, which assessed each strain individually using data from the 2012−2019 seasons. Probabilistic sensitivity analysis assessed the robustness of the results with respect to variation in absolute VE, relative VE, number of egg-adapted seasons, and economic parameters. QIVe + aTIV was cost-saving compared with the baseline scenario (QIVe for all), and QIVe + HD − QIV was not cost-effective in the majority of simulations, reflecting the high acquisition cost of HD − QIV. Overall, while the incremental benefits may vary by influenza season, QIVc + aTIV resulted in the greatest reductions in cases, hospitalizations, and mortality, and was cost-effective (ICER < CAD 50,000) in all simulations.

Assessment of influenza A (H1N1, H3N2) oseltamivir resistance during 2017-2019 in Iran

Background and Objectives

Neuraminidase inhibitors (NAIs) as an imperative antiviral for influenza prophylaxis and treatment are being consumed worldwide. Increasing use of these antivirals might be associated with drug resistance. Regarding the significance of these variations, this study aimed to investigate the mutations occurring in the NA gene of influenza A viruses leading to oseltamivir resistance during 2017-2019 in Iran.

Materials and Methods

In this cross-sectional study, 40 influenza A (H1N1, H3N2) strains, isolated in National Influenza Center (NIC) from patients with Severe Acute Respiratory Infection (SARI) during 2017-2019 were subjected to RT-PCR and sequencing of NA complete gene. The frequency of oseltamivir resistance and variation of NA amino acids in these strains were investigated.

Results

No significant mutation conferring oseltamivir resistance was detected. However, NA antigenic sites in these strains depicted minor changes compared to the vaccine strains. Among H3N2 isolates, mutations at 329, 344, 346 and 385 and among H1N1 isolates mutations at 143 and 188 residues occurred in NA antigenic regions.

Conclusion

Evaluation of NA gene sequences, showed no resistant viruses to oseltamivir. Given that the viruses in the present study were the last viruses circulating in Iran before COVID-19 pandemic, the results will be beneficial to have a worthy comparison with the strains circulating after the pandemic. Constant monitoring for the emergence of drug-resistant variants and antigenic changes are crucial for all countries.

The Pre-Existing Human Antibody Repertoire to Computationally Optimized Influenza H1 Hemagglutinin Vaccines

Computationally optimized broadly reactive Ag (COBRA) hemagglutinin (HA) immunogens have previously been generated for several influenza subtypes to improve vaccine-elicited Ab breadth. As nearly all individuals have pre-existing immunity to influenza viruses, influenza-specific memory B cells will likely be recalled upon COBRA HA vaccination. We determined the epitope specificity and repertoire characteristics of pre-existing human B cells to H1 COBRA HA Ags. Cross-reactivity between wild-type HA and H1 COBRA HA proteins P1, X6, and Y2 were observed for isolated mAbs. The mAbs bound five distinct epitopes on the pandemic A/California/04/2009 HA head and stem domains, and most mAbs had hemagglutination inhibition and neutralizing activity against 2009 pandemic H1 strains. Two head-directed mAbs, CA09-26 and CA09-45, had hemagglutination inhibition and neutralizing activity against a prepandemic H1 strain. One mAb, P1-05, targeted the stem region of H1 HA, but did not compete with a known stem-targeting H1 mAb. We determined that mAb P1-05 recognizes a recently discovered HA epitope, the anchor epitope, and we identified similar mAbs using B cell repertoire sequencing. In addition, the trimerization domain distance from HA was critical to recognition of this epitope by mAb P1-05, suggesting the importance of protein design for vaccine formulations. Overall, these data indicate that seasonally vaccinated individuals possess a population of functional H1 COBRA HA-reactive B cells that target head, central stalk, and anchor epitopes, and they demonstrate the importance of structure-based assessment of subunit protein vaccine candidates to ensure accessibility of optimal protein epitopes.

Seasonal influenza vaccination expands hemagglutinin-specific antibody breadth to older and future A/H3N2 viruses

History of influenza A/H3N2 exposure, especially childhood infection, shape antibody responses after influenza vaccination and infection, but have not been extensively studied. We investigated the breadth and durability of influenza A/H3N2-specific hemagglutinin-inhibition antibodies after live-attenuated influenza vaccine in children (aged 3-17 years, n = 42), and after inactivated influenza vaccine or infection in adults (aged 22-61 years, n = 42) using 14 antigenically distinct A/H3N2 viruses circulating from 1968 to 2018. We found that vaccination and infection elicited cross-reactive antibody responses, predominantly directed against newer or future strains. Childhood H3-priming increased the breadth and magnitude of back-boosted A/H3N2-specific antibodies in adults. Broader and more durable A/H3N2-specific antibodies were observed in repeatedly vaccinated adults than in children and previously unvaccinated adults. Our findings suggest that early A/H3N2 exposure and frequent seasonal vaccination could increase the breadth and seropositivity of antibody responses, which may improve vaccine protection against future viruses.

An epitope-optimized human H3N2 influenza vaccine induces broadly protective immunity in mice and ferrets

There is a crucial need for an improved H3N2 influenza virus vaccine due to low vaccine efficacy rates and increased morbidity and mortality associated with H3N2-dominated influenza seasons. Here, we utilize a computational design strategy to produce epitope-optimized, broadly cross-reactive H3 hemagglutinins in order to create a universal H3N2 influenza vaccine. The Epigraph immunogens are designed to maximize the viral population frequency of epitopes incorporated into the immunogen. We compared our Epigraph H3 vaccine to the traditional egg-based inactivated influenza vaccine from 2018-19, FluZone. Epigraph vaccination-induced stronger cross-reactive antibody responses than FluZone against 18 H3N2 viruses isolated from 1968 to 2019 in both mice and ferrets, with protective hemagglutination inhibition titers against 93-100% of the contemporary H3N2 strains compared to only 27% protection measured from FluZone. In addition, Epigraph vaccination-induced strong cross-reactive T-cell immunity which significantly contributes to protection against lethal influenza virus infection. Finally, Epigraph vaccination protected ferrets from influenza disease after challenge with two H3N2 viruses. The superior cross-reactive immunity induced by these Epigraph immunogens supports their development as a universal H3N2 influenza vaccine.

Current Opinion in LAIV: A Matter of Parent Virus Choice

Influenza is still a frequent seasonal infection of the upper respiratory tract, which may have deadly consequences, especially for the elderly. This is in spite of the availability of vaccines suggested for persons above 65 years of age. Two types of conventional influenza vaccines are currently licensed for use-live attenuated and inactivated vaccines. Depending on local regulatory requirements, live attenuated vaccines are produced by the reverse genetics technique or by classical reassortment in embryonated chicken eggs. Sometimes, the efficiency of classical reassortment is complicated by certain properties of the wild-type parent virus. Cases of low efficacy of vaccines have been noted, which, among other reasons, may be associated with suboptimal properties of the wild-type parent virus that are not considered when recommendations for influenza vaccine composition are made. Unfortunately, knowledge surrounding the roles of properties of the circulating influenza virus and its impact on the efficacy of the reassortment process, vaccination efficiency, the infectivity of the vaccine candidates, etc., is now scattered in different publications. This review summarizes the main features of the influenza virus that may dramatically affect different aspects of the preparation of egg-derived live attenuated vaccine candidates and their effectiveness. The author expresses her personal view, which may not coincide with the opinion of other experts in the field of influenza vaccines.

Antigenic and virological properties of an H3N2 variant that continues to dominate the 2021-22 Northern Hemisphere influenza season

Influenza viruses circulated at very low levels during the beginning of the COVID-19 pandemic, and population immunity against these viruses is low. An H3N2 strain (3C.2a1b.2a2) with a hemagglutinin (HA) that has several substitutions relative to the 2021-22 H3N2 vaccine strain is dominating the 2021-22 Northern Hemisphere influenza season. Here, we show that one of these substitutions eliminates a key glycosylation site on HA and alters sialic acid binding. Using glycan array profiling, we show that the 3C.2a1b.2a2 H3 maintains binding to an extended biantennary sialoside and replicates to high titers in human airway cells. We find that antibodies elicited by the 2021-22 Northern Hemisphere influenza vaccine poorly neutralize the 3C.2a1b.2a2 H3N2 strain. Together, these data indicate that 3C.2a1b.2a2 H3N2 viruses efficiently replicate in human cells and escape vaccine-elicited antibodies.

STING agonist-containing microparticles improve seasonal influenza vaccine efficacy and durability in ferrets over standard adjuvant

The current pandemic highlights the need for effective vaccines against respiratory viruses. An ideal vaccine should induce robust and long-lasting responses with high manufacturing scalability. We use an adjuvant comprised of a Stimulator of Interferon Genes (STING) agonist incorporated in a scalable microparticle platform to achieve durable protection against the influenza virus. This formulation overcomes the challenges presented by the cytosolic localization of STING and the hydrophilicity of its agonists. We evaluated a monoaxial formulation of polymeric acetalated dextran microparticles (MPs) to deliver the STING agonist cyclic GMP-AMP (cGAMP) which achieved >10× dose-sparing effects compared to other published work. Efficacy was evaluated in ferrets, a larger animal model of choice for influenza vaccines. cGAMP MPs with recombinant hemagglutinin reduced viral shedding and improved vaccine outcomes compared to a seasonal influenza vaccine. Importantly, sustained protection against a lethal influenza infection was detected a year after a single dose of the vaccine-adjuvant.

Generation and characterization of monoclonal antibodies against the hemagglutinin of H3N2 influenza A viruses

Seasonal influenza viruses are highly contagious, leading to 290,000-650,000 mortalities every year globally. Among the influenza viruses, influenza A virus (H3N2) has attracted much attention due to its high frequency of antigenic variations, resulting in poor protection by vaccination. We generated a panel of murine neutralizing monoclonal antibodies (mAbs) against A/Texas/50/2012 (H3N2) and identified the relevant epitopes that potentially influence the antigenicity by selecting mAb-resistant mutants. The epitopes were mainly in antigenic site A (1/9, 11.1%), B (6/9, 66.7%), and C (1/9, 11.1%), which is consistent with recent reports on the immunodominance of antigenic site B. The amino acid substitutions at positions 156, 157, 159, 160, and 189 at antigenic site B resulted in decreased mAb capability for blocking receptor binding. In addition, the neutralizing spectra of three mAbs (1F8, 1G9 and 1H5) were different, suggesting that their epitopes may be different but partially overlapping, and it required further study. Further, the mAb 3F9 selected a new substitution, D53G/N, at antigenic site C and showed in vitro neutralizing activity against A/Victoria/361/2011 (H3N2), A/Texas/50/2012 (H3N2), and A/Hong Kong/2671/2019 (H3N2), suggesting a potential epitope on H3 hemagglutinin for inducing broad neutralizing antibody responses. Continuous research and regular monitoring of novel epitopes are of great importance for improving vaccine strain selection.

Suitability of NIID-MDCK cells as a substrate for cell-based influenza vaccine development from the perspective of adventitious virus susceptibility

The practical use of cell-based seasonal influenza vaccines is currently being considered in Japan. From the perspective of adventitious virus contamination, we assessed the suitability of NIID-MDCK cells (NIID-MDCK-Cs) as a safe substrate for the isolation of influenza viruses from clinical specimens. We first established a sensitive multiplex real-time PCR system to screen for 27 respiratory viruses and used it on 34 virus samples that were isolated by passaging influenza-positive clinical specimens in NIID-MDCK-Cs. Incidentally, the limit of detection of the system was 100 or fewer genome copies per reaction. In addition to influenza viruses, human enterovirus 68 (HEV-D68) genomes were detected in two samples after two or three passages in NIID-MDCK-Cs. To further investigate the susceptibility of NIID-MDCK-Cs to adventitious viruses, eight common respiratory viruses were subjected to passages in NIID-MDCK-Cs. The genome copy numbers of seven viruses other than parainfluenza 3 decreased below the limit of detection (LOD) by passage 4. By passaging in NIID-MDCK-Cs, the genome numbers of the input HEV-D68, 1 x 10⁸ copies, declined to 10² at passage 3 and to under the LOD at passage 4, whereas those of the other six viruses were under the LOD by passage 3. These results implied that during the process of isolating influenza viruses with NIID-MDCK-Cs, contaminating viruses other than parainfluenza 3 can be efficiently removed by passages in NIID-MDCK-Cs. NIID-MDCK-Cs could be a safe substrate for isolating influenza viruses that can be used to develop cell-based influenza vaccine candidate viruses. This article is protected by copyright. All rights reserved.

A single-shot adenoviral vaccine provides hemagglutinin stalk-mediated protection against heterosubtypic influenza challenge in mice

Conventional influenza vaccines fail to confer broad protection against diverse influenza A viruses with pandemic potential. Efforts to develop a universal influenza virus vaccine include refocusing immunity towards the highly conserved stalk domain of the influenza virus surface glycoprotein, hemagglutinin (HA). We constructed a non-replicating adenoviral (Ad) vector, encoding a secreted form of H1 HA, to evaluate HA stalk-focused immunity. The Ad5_H1 vaccine was tested in mice for its ability to elicit broad, cross-reactive protection against homologous, heterologous, and heterosubtypic lethal challenge in a single-shot immunization regimen. Ad5_H1 elicited hemagglutination inhibition (HI+) active antibodies (Abs), which conferred 100% sterilizing protection from homologous H1N1 challenge. Furthermore, Ad5_H1 rapidly induced H1-stalk-specific Abs with Fc-mediated effector function activity, in addition to stimulating both CD4+ and CD8+ stalk-specific T cell responses. This phenotype of immunity provided 100% protection from lethal challenge with a head-mismatched, reassortant influenza virus bearing a chimeric HA, cH6/1, in a stalk-mediated manner. Most importantly, 100% protection from mortality following lethal challenge with a heterosubtypic avian influenza virus, H5N1, was observed following a single immunization with Ad5_H1. In conclusion, Ad-based influenza vaccines can elicit significant breadth of protection in naive animals and could be considered for pandemic preparedness and stockpiling.

Evaluation of determinants of the serological response to the quadrivalent split-inactivated influenza vaccine

The seasonal influenza vaccine is only effective in half of the vaccinated population. To identify determinants of vaccine efficacy, we used data from > 1,300 vaccination events to predict the response to vaccination measured as seroconversion as well as hemagglutination inhibition (HAI) titer levels one year after. We evaluated the predictive capabilities of age, body mass index (BMI), sex, race, comorbidities, vaccination history, and baseline HAI titers, as well as vaccination month and vaccine dose in multiple linear regression models. The models predicted the categorical response for > 75% of the cases in all subsets with one exception. Prior vaccination, baseline titer level, and age were the major determinants of seroconversion, all of which had negative effects. Further, we identified a gender effect in older participants and an effect of vaccination month. BMI had a surprisingly small effect, likely due to its correlation with age. Comorbidities, vaccine dose, and race had negligible effects. Our models can generate a new seroconversion score that is corrected for the impact of these factors which can facilitate future biomarker identification.

Influenza Vaccine Effectiveness by A(H3N2) Phylogenetic Subcluster and Prior Vaccination History: 2016-2017 and 2017-2018 Epidemics in Canada

BACKGROUND

The influenza A(H3N2) vaccine was updated from clade 3C.3a in 2015-2016 to 3C.2a for 2016-2017 and 2017-2018. Circulating 3C.2a viruses showed considerable hemagglutinin glycoprotein diversification and the egg-adapted vaccine also bore mutations.

METHODS

Vaccine effectiveness (VE) in 2016-2017 and 2017-2018 was assessed by test-negative design, explored by A(H3N2) phylogenetic subcluster and prior season's vaccination history.

RESULTS

In 2016-2017, A(H3N2) VE was 36% (95% confidence interval [CI], 18%-50%), comparable with (43%; 95% CI, 24%-58%) or without (33%; 95% CI, -21% to 62%) prior season's vaccination. In 2017-2018, VE was 14% (95% CI, -8% to 31%), lower with (9%; 95% CI, -18% to 30%) versus without (45%; 95% CI, -7% to 71%) prior season's vaccination. In 2016-2017, VE against predominant clade 3C.2a1 viruses was 33% (95% CI, 11%-50%): 18% (95% CI, -40% to 52%) for 3C.2a1a defined by a pivotal T135K loss of glycosylation; 60% (95% CI, 19%-81%) for 3C.2a1b (without T135K); and 31% (95% CI, 2%-51%) for other 3C.2a1 variants (with/without T135K). VE against 3C.2a2 viruses was 45% (95% CI, 2%-70%) in 2016-2017 but 15% (95% CI, -7% to 33%) in 2017-2018 when 3C.2a2 predominated. VE against 3C.2a1b in 2017-2018 was 37% (95% CI, -57% to 75%), lower at 12% (95% CI, -129% to 67%) for a new 3C.2a1b subcluster (n = 28) also bearing T135K.

CONCLUSIONS

Exploring VE by phylogenetic subcluster and prior vaccination history reveals informative heterogeneity. Pivotal mutations affecting glycosylation sites, and repeat vaccination using unchanged antigen, may reduce VE.

Drop the Needle; A Temperature Stable Oral Tablet Vaccine Is Protective against Respiratory Viral Pathogens

To effectively combat emerging infections and prevent future pandemics, next generation vaccines must be developed quickly, manufactured rapidly, and most critically, administered easily. Next generation vaccines need innovative approaches that prevent infection, severe disease, and reduce community transmission of respiratory pathogens such as influenza and SARS-CoV-2. Here we review an oral vaccine tablet that can be manufactured and released in less than 16 weeks of antigen design and deployed without the need for cold chain. The oral Ad5 modular vaccine platform utilizes a non-replicating adenoviral vector (rAd5) containing a novel molecular TLR3 adjuvant that is delivered by tablet, not by needle. This enterically coated, room temperature-stable vaccine tablet elicits robust antigen-specific IgA in the gastrointestinal and respiratory tracts and upregulates mucosal homing adhesion molecules on circulating B and T cells. Several influenza antigens have been tested using this novel vaccine approach and demonstrated efficacy in both preclinical animal models and in phase I/II clinical trials, including in a human challenge study. This oral rAd5 vaccine platform technology offers a promising new avenue for aiding in rapid pandemic preparedness and equitable worldwide vaccine distribution.

Precision Vaccine Development: Cues From Natural Immunity

Traditional vaccine development against infectious diseases has been guided by the overarching aim to generate efficacious vaccines normally indicated by an antibody and/or cellular response that correlates with protection. However, this approach has been shown to be only a partially effective measure, since vaccine- and pathogen-specific immunity may not perfectly overlap. Thus, some vaccine development strategies, normally focused on targeted generation of both antigen specific antibody and T cell responses, resulting in a long-lived heterogenous and stable pool of memory lymphocytes, may benefit from better mimicking the immune response of a natural infection. However, challenges to achieving this goal remain unattended, due to gaps in our understanding of human immunity and full elucidation of infectious pathogenesis. In this review, we describe recent advances in the development of effective vaccines, focusing on how understanding the differences in the immunizing and non-immunizing immune responses to natural infections and corresponding shifts in immune ontogeny are crucial to inform the next generation of infectious disease vaccines.

The Antibody Response Against Neuraminidase in Human Influenza A (H3N2) Virus Infections During 2018/2019 Flu Season: Focusing on the Epitopes of 329-N-Glycosylation and E344 in N2

Seasonal influenza A (H3N2) virus has been a concern since its first introduction in humans in 1968. Accumulating antigenic changes in viral hemagglutinin (HA), particularly recent cocirculations of multiple HA genetic clades, allow H3N2 virus evade into humans annually. From 2010, the binding of neuraminidase (NA) to sialic acid made the traditional assay for HA inhibition antibodies (Abs) unsuitable for antigenicity characterization. Here, we investigated the serum anti-NA response in a cohort with a seroconversion of microneutralizing (MN) Abs targeting the circulating strain, A/Singapore/INFIMH-16-0019/2016 (H3N2, 3C.2a1)-like, a virus during 2018/2019 flu seasons. We discovered that MN Ab titers show no difference between children and adults. Nevertheless, higher titers of Abs with NA activity inhibition (NI) activity of 129 and seroconversion rate of 68.42% are presented in children aged 7-17 years (n = 19) and 73.47 and 41.17% in adults aged 21-59 years (n = 17), respectively. The MN Abs generated in children display direct correlations with HA- and NA-binding Abs or NI Abs. The NI activity exhibited cross-reactivity to N2 of H3N2 viruses of 2007 and 2013, commonly with 329-N-glycosylation and E344 in N2, a characteristic of earlier 3C.2a H3N2 virus in 2014. The percentage of such viruses pronouncedly decreased and was even replaced by those dominant H3N2 viruses with E344K and 329 non-glycosylation, which have a significantly low activity to the tested antisera. Our findings suggest that NI assay is a testable assay applied in H3N2 infection in children, and the antigenic drift of current N2 should be considered for vaccine selection.

Antigenic characterization of influenza and SARS-CoV-2 viruses

Antigenic characterization of emerging and re-emerging viruses is necessary for the prevention of and response to outbreaks, evaluation of infection mechanisms, understanding of virus evolution, and selection of strains for vaccine development. Primary analytic methods, including enzyme-linked immunosorbent/lectin assays, hemagglutination inhibition, neuraminidase inhibition, micro-neutralization assays, and antigenic cartography, have been widely used in the field of influenza research. These techniques have been improved upon over time for increased analytical capacity, and some have been mobilized for the rapid characterization of the SARS-CoV-2 virus as well as its variants, facilitating the development of highly effective vaccines within 1 year of the initially reported outbreak. While great strides have been made for evaluating the antigenic properties of these viruses, multiple challenges prevent efficient vaccine strain selection and accurate assessment. For influenza, these barriers include the requirement for a large virus quantity to perform the assays, more than what can typically be provided by the clinical samples alone, cell- or egg-adapted mutations that can cause antigenic mismatch between the vaccine strain and circulating viruses, and up to a 6-month duration of vaccine development after vaccine strain selection, which allows viruses to continue evolving with potential for antigenic drift and, thus, antigenic mismatch between the vaccine strain and the emerging epidemic strain. SARS-CoV-2 characterization has faced similar challenges with the additional barrier of the need for facilities with high biosafety levels due to its infectious nature. In this study, we review the primary analytic methods used for antigenic characterization of influenza and SARS-CoV-2 and discuss the barriers of these methods and current developments for addressing these challenges.

Phase 3 Randomized, Multicenter, Placebo-Controlled Study to Evaluate Safety, Immunogenicity, and Lot-to-Lot Consistency of an Adjuvanted Cell Culture-Derived, H5N1 Subunit Influenza Virus Vaccine in Healthy Adult Subjects

A cell-based process may be better suited for vaccine production during a highly pathogenic avian influenza (HPAI) pandemic. This was a phase 3, randomized, controlled, observer-blind, multicenter study evaluated safety, immunogenicity, and lot-to-lot consistency of two doses of a MF59-adjuvanted, H5N1 influenza pandemic vaccine manufactured on a cell culture platform (aH5N1c) in 3196 healthy adult subjects, stratified into two age groups: 18 to <65 and ≥65 years. Immunogenicity was measured using hemagglutination inhibition (HI) titers. HI antibody responses increased after the first aH5N1c vaccine dose, and 3 weeks after the second vaccination (Day 43), age-appropriate US Center for Biologics Evaluation and Research (CBER) and former European Medicines Authority Committee for Medicinal Products for Human Use (EMA CHMP) immunogenicity criteria were met. Six months after the first vaccination, HI titers were above baseline but no longer met CBER and CHMP criteria. No relevant changes over time were seen in placebo subjects. Solicited AEs were more frequent in the active treatment than the placebo group, primarily due to injection site pain. No serious adverse events (SAEs) related to aH5N1c- were reported. aH5N1c influenza vaccine elicited high levels of antibodies following two vaccinations administered 21 days apart and met both CBER and former CHMP immunogenicity criteria at Day 43 among both younger and older adults with a clinically acceptable safety profile. Consistency of the three consecutive aH5N1c vaccine lots was demonstrated (NCT02839330).

Female-biased effects of aging on a chimeric hemagglutinin stalk-based universal influenza virus vaccine in mice

To determine if biological sex and age intersect to affect universal influenza vaccine-induced immunity, adult and aged male and female C57BL/6 mice were sequentially immunized with a chimeric-hemagglutinin (cHA) stalk-based H1 vaccine. Adult mice developed greater quantity and quality of H1-stalk antibodies, that were more cross-reactive with other group 1, but not group 2, influenza viruses, than aged mice. The vaccine did not induce neutralizing or hemagglutination inhibition antibodies, but rather antibody-dependent cellular cytotoxicity, which was greater in adult than aged mice. Vaccinated adult mice were better protected than aged mice after challenge with 2009 H1N1 virus, experiencing less morbidity and having lower pulmonary virus titers. The age-associated decline in immunity and protection was consistently greater among females than males, with the reduction in immunity and protection for aged as compared with adult females often being the sole comparison driving the overall age-associated significant differences. The age-associated reduction in stalk-based immunity in females was not, however, associated with changes in estradiol. To determine if the better antibodies in adults could be utilized to protect aged mice, serum was passively transferred from vaccinated adult mice into naïve sex-matched aged mice. Even with transferred serum from young adult mice, aged females still suffered greater morbidity than aged males. These data suggest there are sex-dependent effects of aging on cHA-based universal influenza virus vaccine-induced immunity that cannot be reversed through transfer of serum from young animals. The lack of consideration of sex-specific effects of aging on immunity could hinder efforts toward universal vaccines.

Strategies for fighting pandemic virus infections: Integration of virology and drug delivery

Respiratory viruses have sometimes resulted in worldwide pandemics, with the influenza virus and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) being major participants. Long-term efforts have made it possible to control the influenza virus, but seasonal influenza continues to take many lives each year, and a pandemic influenza virus sometimes emerges. Although vaccines for coronavirus disease 2019 (COVID-19) have been developed, we are not yet able to coexist with the SARS-CoV-2. To overcome such viruses, it is necessary to obtain knowledge about international surveillance systems, virology, ecology and to determine that immune responses are effective. The information must then be transferred to drugs. Delivery systems would be expected to contribute to the rational development of drugs. In this review, virologist and drug delivery system (DDS) researchers discuss drug delivery strategies, especially the use of lipid-based nanocarriers, for fighting to respiratory virus infections.

Influenza virus infection history shapes antibody responses to influenza vaccination

Studies of successive vaccination suggest that immunological memory against past influenza viruses may limit responses to vaccines containing current strains. The impact of memory induced by prior infection is rarely considered and is difficult to ascertain, because infections are often subclinical. This study investigated influenza vaccination among adults from the Ha Nam cohort (Vietnam), who were purposefully selected to include 72 with and 28 without documented influenza A(H3N2) infection during the preceding 9 years (Australian New Zealand Clinical Trials Registry 12621000110886). The primary outcome was the effect of prior influenza A(H3N2) infection on hemagglutinin-inhibiting antibody responses induced by a locally available influenza vaccine administered in November 2016. Baseline and postvaccination sera were titrated against 40 influenza A(H3N2) strains spanning 1968-2018. At each time point (baseline, day 14 and day 280), geometric mean antibody titers against 2008-2018 strains were higher among participants with recent infection (34 (29-40), 187 (154-227) and 86 (72-103)) than among participants without recent infection (19 (17-22), 91 (64-130) and 38 (30-49)). On days 14 and 280, mean titer rises against 2014-2018 strains were 6.1-fold (5.0- to 7.4-fold) and 2.6-fold (2.2- to 3.1-fold) for participants with recent infection versus 4.8-fold (3.5- to 6.7-fold) and 1.9-fold (1.5- to 2.3-fold) for those without. One of 72 vaccinees with recent infection versus 4 of 28 without developed symptomatic A(H3N2) infection in the season after vaccination (P = 0.021). The range of A(H3N2) viruses recognized by vaccine-induced antibodies was associated with the prior infection strain. These results suggest that recall of immunological memory induced by prior infection enhances antibody responses to inactivated influenza vaccine and is important to attain protective antibody titers.

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.

A randomized controlled trial of antibody response to 2019-20 cell-based inactivated and egg-based live attenuated influenza vaccines in children and young adults

BACKGROUND

Hemagglutination inhibition (HAI) titers to the live-attenuated influenza vaccine (LAIV4) are typically lower than its counterpart egg-based inactivated influenza vaccines (IIV). Similar comparisons have not been made between LAIV4 and the 4-strain, cell-culture inactivated influenza vaccine (ccIIV4). We compared healthy children's and young adults' HAI titers against the 2019-2020 LAIV4 and ccIIV4.

METHODS

Participants aged 4-21 years were randomized 1:1 to receive ccIIV4 (n = 100) or LAIV4 (n = 98). Blood was drawn prevaccination and on day 28 (21-35) post vaccination. HAI assays against egg-grown A/H1N1, A/H3N2, both vaccine B strains and cell-grown A/H3N2 antigens were conducted. Primary outcomes were geometric mean titers (GMT) and geometric mean fold rise (GMFR) in titers.

RESULTS

GMTs to A/H1N1, A/H3N2 and B/Victoria increased following both ccIIV and LAIV and to B/Yamagata following ccIIV (p < 0.05). The GMFR range was 2.4-3.0 times higher for ccIIV4 than for LAIV4 (p < 0.001). Within vaccine types, egg-grown A/H3N2 GMTs were higher (p < 0.05) than cell-grown GMTs [ccIIV4 day 28: egg = 205 (95% CI: 178-237); cell = 136 (95% CI:113-165); LAIV4 day 28: egg = 96 (95% CI: 83-112); cell = 63 (95% CI: 58-74)]. The GMFR to A/H3N2 cell-grown and egg-grown antigens were similar. Pre-vaccination titers inversely predicted GMFR.

CONCLUSION

The HAI response to ccIIV4 was greater than LAIV4 in this study of mostly older children, and day 0 HAI titers inversely predicted GMFR for both vaccines. Lower prevaccination titers were associated with greater GMFR in both vaccine groups.

Bioengineered pseudovirus nanoparticles displaying the HA1 antigens of influenza viruses for enhanced immunogenicity

Even with implementation of current influenza vaccines, influenza still claims up to 500,000 lives worldwide annually, indicating a need for a better vaccine strategy. We have developed a technology to generate unique S60-HA1 pseudovirus nanoparticles (PVNPs) that display the receptor-binding HA1 domains of influenza viruses. Each self-assembled S60-HA1 PVNP consists of a T = 1 icosahedral S60 nanoparticle that resembles the inner shell of norovirus capsid and 60 surface-displayed HA1 antigens that are excellent vaccine targets. Soluble S60-HA1 PVNPs presenting HA1 antigens of H7N9 influenza virus subtypes have been produced efficiently in large amount. Their three-dimensional (3D) structures have been solved by cryogenic electron microscopy. The PVNP-displayed HA1 antigens react with HA-specific antibody, and retain authentic sialic acid binding specificity and hemagglutinate human erythrocytes. The PVNPs are highly immunogenic, eliciting high titers of HA1-specific antibodies in mice and the mouse sera strongly inhibited hemagglutinations of homologous and heterologous influenza virus HA proteins. Therefore, the S60-HA1 PVNPs may provide useful reagents to study influenza viruses and offer a potential new vaccine tactic to fight the deadly influenza disease.

A Real-World Clinical and Economic Analysis of Cell-Derived Quadrivalent Influenza Vaccine Compared to Standard Egg-Derived Quadrivalent Influenza Vaccines During the 2019-2020 Influenza Season in the United States

Background

Cell-derived influenza vaccines are not subject to egg-adaptive mutations that have potential to decrease vaccine effectiveness. This retrospective analysis estimated the relative vaccine effectiveness (rVE) of cell-derived quadrivalent influenza vaccine (IIV4c) compared to standard egg-derived quadrivalent influenza vaccines (IIV4e) among recipients aged 4-64 years in the United States during the 2019-2020 influenza season.

Methods

The IQVIA PharMetrics Plus administrative claims database was utilized. Study outcomes were assessed postvaccination through the end of the study period (7 March 2020). Inverse probability of treatment weighting (IPTW) was implemented to adjust for covariate imbalance. Adjusted rVE against influenza-related hospitalizations/emergency room (ER) visits and other clinical outcomes was estimated through IPTW-weighted Poisson regression models for the IIV4c and IIV4e cohorts and for the subgroup with ≥1 high-risk condition. Sensitivity analyses modifying the outcome assessment period as well as a doubly-robust analysis were also conducted. IPTW-weighted generalized linear models were used to estimate predicted annualized all-cause costs.

Results

The final sample comprised 1 150 134 IIV4c and 3 924 819 IIV4e recipients following IPTW adjustment. IIV4c was more effective in preventing influenza-related hospitalizations/ER visits as well as respiratory-related hospitalizations/ER visits compared to IIV4e. IIV4c was also more effective for the high-risk subgroup and across the sensitivity analyses. IIV4c was also associated with significantly lower annualized all-cause total costs compared to IIV4e (-$467), driven by lower costs for outpatient medical services and inpatient hospitalizations.

Conclusions

IIV4c was significantly more effective in preventing influenza-related hospitalizations/ER visits compared to IIV4e and was associated with significantly lower all-cause costs.

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.

Characterization of a 2016-2017 Human Seasonal H3 Influenza A Virus Spillover Now Endemic to U.S. Swine

In 2017, the Iowa State University Veterinary Diagnostic Laboratory detected a reverse-zoonotic transmission of a human seasonal H3 influenza A virus into swine (IAV-S) in Oklahoma. Pairwise comparison between the recently characterized human seasonal H3 IAV-S (H3.2010.2) hemagglutinin (HA) sequences detected in swine and the most similar 2016-2017 human seasonal H3 revealed 99.9% nucleotide identity. To elucidate the origin of H3.2010.2 IAV-S, 45 HA and 27 neuraminidase (NA) sequences from 2017 to 2020 as well as 11 whole-genome sequences (WGS) were genetically characterized. Time to most recent common human ancestor was estimated between August and September 2016. The N2 NA was of human origin in all but one strain from diagnostic submissions with NA sequences, and the internal gene segments from WGS consisted of matrix genes originating from the 2009 pandemic H1N1 and another 5 internal genes of triple reassortant swine origin (TTTTPT). Pigs experimentally infected with H3.2010.2 demonstrated efficient nasal shedding and replication in the lungs, mild pneumonia, and minimal microscopic lung lesions and transmitted the virus to indirect contact swine. Antigenically, H3.2010.2 viruses were closer to a human seasonal vaccine strain, A/Hong Kong/4801/2014, than to the H3.2010.1 human seasonal H3 viruses detected in swine in 2012. This was the second sustained transmission of a human seasonal IAV into swine from the 2010 decade after H3.2010.1. Monitoring the spillover and detection of novel IAV from humans to swine may help vaccine antigen selection and could impact pandemic preparedness. IMPORTANCE H3.2010.2 is a new phylogenetic clade of H3N2 circulating in swine that became established after the spillover of a human seasonal H3N2 from the 2016-2017 influenza season. The novel H3.2010.2 transmitted and adapted to the swine host and demonstrated reassortment with internal genes from strains endemic to pigs, but it maintained human-like HA and NA. It is genetically and antigenically distinct from the H3.2010.1 H3N2 introduced earlier in the 2010 decade. Human seasonal IAV spillovers into swine become established in the population through adaptation and sustained transmission and contribute to the genetic and antigenic diversity of IAV circulating in swine. Continued IAV surveillance is necessary to detect emergence of novel strains in swine and assist with vaccine antigen selection to improve the ability to prevent respiratory disease in swine as well as the risk of zoonotic transmission.

mRNA-Based Vaccines and Mode of Action

In the past 20 years, the mRNA vaccine technology has evolved from the first proof of concept to the first licensed vaccine against emerging pandemics such as SARS-CoV-2. Two mRNA vaccines targeting SARS-CoV-2 have received emergency use authorization by US FDA, conditional marketing authorization by EMA, as well as multiple additional national regulatory authorities. The simple composition of an mRNA encoding the antigen formulated in a lipid nanoparticle enables a fast adaptation to new emerging pathogens. This can speed up vaccine development in pandemics from antigen and sequence selection to clinical trial to only a few months. mRNA vaccines are well tolerated and efficacious in animal models for multiple pathogens and will further contribute to the development of vaccines for other unaddressed diseases. Here, we give an overview of the mRNA vaccine design and factors for further optimization of this new promising technology and discuss current knowledge on the mode of action of mRNA vaccines interacting with the innate and adaptive immune system.

Messenger RNA-Based Vaccines Against Infectious Diseases

In vitro-transcribed, messenger RNA-based infectious disease vaccines have the potential to successfully address many of the weaknesses of traditional vaccine platforms, such as the lack of potency and/or durability of vaccine protection, time-consuming, and expensive manufacturing, and, in some cases, safety issues. This optimism is fueled by a great deal of impressive recent data demonstrating that mRNA vaccines have many of the attributes that are necessary for a viable new vaccine class for human use. This review briefly describes mRNA vaccine types, discusses the most relevant and recent publications on infectious disease mRNA vaccines, and highlights the hurdles that need to be overcome to bring this promising novel vaccine modality to the clinic.

Self-amplifying mRNA-Based Vaccine Technology and Its Mode of Action

Self-amplifying mRNAs derived from the genomes of positive-strand RNA viruses have recently come into focus as a promising technology platform for vaccine development. Non-virally delivered self-amplifying mRNA vaccines have the potential to be highly versatile, potent, streamlined, scalable, and inexpensive. By amplifying their genome and the antigen encoding mRNA in the host cell, the self-amplifying mRNA mimics a viral infection, resulting in sustained levels of the target protein combined with self-adjuvanting innate immune responses, ultimately leading to potent and long-lasting antigen-specific humoral and cellular immune responses. Moreover, in principle, any eukaryotic sequence could be encoded by self-amplifying mRNA without the need to change the manufacturing process, thereby enabling a much faster and flexible research and development timeline than the current vaccines and hence a quicker response to emerging infectious diseases. This chapter highlights the rapid progress made in using non-virally delivered self-amplifying mRNA-based vaccines against infectious diseases in animal models. We provide an overview of the unique attributes of this vaccine approach, summarize the growing body of work defining its mechanism of action, discuss the current challenges and latest advances, and highlight perspectives about the future of this promising technology.

Vaccine-Associated Enhanced Disease and Pathogenic Human Coronaviruses

Vaccine-associated enhanced disease (VAED) is a difficult phenomenon to define and can be confused with vaccine failure. Using studies on respiratory syncytial virus (RSV) vaccination and dengue virus infection, we highlight known and theoretical mechanisms of VAED, including antibody-dependent enhancement (ADE), antibody-enhanced disease (AED) and Th2-mediated pathology. We also critically review the literature surrounding this phenomenon in pathogenic human coronaviruses, including MERS-CoV, SARS-CoV-1 and SARS-CoV-2. Poor quality histopathological data and a lack of consistency in defining severe pathology and VAED in preclinical studies of MERS-CoV and SARS-CoV-1 vaccines in particular make it difficult to interrogate potential cases of VAED. Fortuitously, there have been only few reports of mild VAED in SARS-CoV-2 vaccination in preclinical models and no observations in their clinical use. We describe the problem areas and discuss methods to improve the characterisation of VAED in the future.

The Development of mRNA Vaccines for Infectious Diseases: Recent Updates

mRNA-based technologies have been of interest for the past few years to be used for therapeutics. Several mRNA vaccines for various diseases have been in preclinical and clinical stages. With the outbreak of the COVID-19 pandemic, the emergence of mRNA vaccines has transformed modern science. Recently, two major mRNA vaccines have been developed and approved by global health authorities for administration on the general population for protection against SARS-CoV-2. They have been proven to be successful in conferring protection against the ongoing SARS-CoV-2 and its emerging variants. This will draw attention to various mRNA vaccines against infectious diseases that are in the early stages of clinical trials. mRNA vaccines offer several advantages ranging from rapid design, generation, manufacturing, and administration and have strong potential to be used against various diseases in the future. Here, we summarize the mRNA-based vaccines in development against various infectious diseases.

Analyses of Safety Profile and Homologous Antibody Responses to a Mammalian Cell-Based, MF59-Adjuvanted, A/H5N1, Pandemic Influenza Vaccine across Four Phase II/III Clinical Trials in Healthy Children, Adults, and Older Adults

Modern cell culture-based technology eliminates vaccine manufactures reliance on embryonated chicken eggs, which may become compromised during an avian influenza pandemic. Four studies (total N = 6230) assessed the immunogenicity and safety of mammalian cell-based, MF59^®-adjuvanted, A/H5N1 vaccine (aH5N1c; AUDENZ™) as two doses administered on Days 1 and 22 in children (NCT01776554), adults (NCT01776541; NCT02839330), and older adults (NCT01766921; NCT02839330). Immunogenicity of formulations at 7.5 μg and 3.75 μg antigen per dose were assessed by hemagglutination inhibition and microneutralization assays on Days 1, 22, 43, and 183 or 387. Solicited local and systemic adverse events (AEs) were recorded for 7 days after each vaccination. Unsolicited AEs were collected for 21 days after each vaccination, and serious and other selected AEs were recorded for one year. Antibody responses after two 7.5 μg doses met CBER licensure criteria in all age groups. Overall, an age-related response was evident, with the highest responses observed in children <3 years old. In children, antibody titers met seroconversion criteria 12 months after vaccination. MF59 allowed for antigen dose sparing. Solicited AEs were mild to moderate in nature, of short duration, and less frequent after the second dose than the first, demonstrating a favorable risk-benefit profile.

Enhanced isolation of influenza viruses in qualified cells improves the probability of well-matched vaccines

Influenza vaccines are utilised to combat seasonal and pandemic influenza. The key to influenza vaccination currently is the availability of candidate vaccine viruses (CVVs). Ideally, CVVs reflect the antigenic characteristics of the circulating virus, which may vary depending upon the isolation method. For traditional inactivated egg-based vaccines, CVVs are isolated in embryonated chicken eggs, while for cell-culture production, CVV's are isolated in either embryonated eggs or qualified cell lines. We compared isolation rates, growth characteristics, genetic stability and antigenicity of cell and egg CVV's derived from the same influenza-positive human clinical respiratory samples collected from 2008-2020. Influenza virus isolation rates in MDCK33016PF cells were twice that of eggs and mutations in the HA protein were common in egg CVVs but rare in cell CVVs. These results indicate that fully cell-based influenza vaccines will improve the choice, match and potentially the effectiveness, of seasonal influenza vaccines compared to egg-based vaccines.

Serologic response to sequential vaccination with enhanced influenza vaccines: Open label randomized trial among adults aged 65-74 years

BACKGROUND

The effects of sequential vaccination with enhanced influenza vaccines are poorly understood. We conducted an exploratory open-label study to assess serologic response to sequential vaccination in older adults.

METHODS

160 adults aged 65 through 74 years were randomized (1:1:1) to receive trivalent inactivated standard dose (SD), high-dose (HD), or MF59-adjuvanted (AD) vaccine in 2016/17. In 2017/18, HD and AD recipients received the same vaccine; SD recipients were re-randomized to HD or AD. Hemagglutination inhibition assays were performed using turkey erythrocytes against A/California/7/2009(H1N1)-like and B/Brisbane/60/2008(B/Victoria)-like in both seasons, and A/Michigan/45/2015(H1N1)-like in season 2. Microneutralization assays were performed against cell-propagated A/Hong Kong/4801/2014(H3N2)-like using MDCK-SIAT1 cells. Postvaccination geometric mean titer (GMT), percent with titer ≥ 40, and mean fold rise (MFR, ratio of postvaccination versus prevaccination titer) in season 2 were compared across groups, and ratio of MFR in season 2 versus season 1 was assessed for each strain.

RESULTS

Analysis included 152 participants (55 HD → HD, 58 AD → AD, 19 SD → HD, and 20 SD → AD). Season 2 postvaccination GMTs and percent with titer ≥ 40 did not differ between HD → HD and AD → AD recipients for vaccine strains examined. However, a higher percent of HD → HD and AD → AD recipients had postvaccination titer ≥ 40 than SD → AD recipients for A/H1N1 (86%-89% versus 60%) and SD → AD and SD → HD recipients for A/H3N2 (83%-87% versus 40%-53%). GMTs were higher in AD → AD versus SD → AD recipients for A/H1N1 (p = .01) and A/H3N2 (p = .002). MFRs in season 2 were low in all groups for A/H3N2 (1.5-2.2) and B/Victoria (1.7-2.3). MFR was lower in season 2 versus 1 for HD → HD and AD → AD recipients for all vaccine strains (1.6-3.7 versus 2.6-6.2).

CONCLUSIONS

Sequential vaccination with enhanced vaccines did not reduce immunogenicity in adults aged 65 through 74 years. Serologic response to cell-propagated A/H3N2 was suboptimal for all vaccines. ClinicalTrials.gov identifier. NCT02872311.

Unique features of a recombinant haemagglutinin influenza vaccine that influence vaccine performance

The influenza vaccine field has been constantly evolving to improve the speed, scalability, and flexibility of manufacturing, and to improve the breadth and longevity of the protective immune response across age groups, giving rise to an array of next generation vaccines in development. Among these, the recombinant influenza vaccine tetravalent (RIV4), using a baculovirus expression vector system to express recombinant haemagglutinin (rHA) in insect cells, is the only one to have reached the market and has been studied extensively. We describe how the unique structural features of rHA in RIV4 improve protective immune responses compared to conventional influenza vaccines made from propagated influenza virus. In addition to the sequence integrity, characteristic of recombinant proteins, unique post-translational processing of the rHA in insect cells instills favourable tertiary and quaternary structural features. The absence of protease-driven cleavage and addition of simple N-linked glycans help to preserve and expose certain conserved epitopes on HA molecules, which are likely responsible for the high levels of broadly cross-reactive and protective antibodies with rare specificities observed with RIV4. Furthermore, the presence of uniform compact HA oligomers and absence of egg proteins, viral RNA or process impurities, typically found in conventional vaccines, are expected to eliminate potential adverse reactions to these components in susceptible individuals with the use of RIV4. These distinct structural features and purity of the recombinant HA vaccine thus provide a number of benefits in vaccine performance which can be extended to other viral targets, such as for COVID-19.

Glycosylation of SARS-CoV-2: structural and functional insights

The COVID-19 pandemic is caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Similar to other coronaviruses, its particles are composed of four structural proteins: spike (S), envelope (E), membrane (M), and nucleocapsid (N) proteins. S, E, and M proteins are glycosylated, and the N protein is phosphorylated. The S protein is involved in the interaction with the host receptor human angiotensin-converting enzyme 2 (hACE2), which is also heavily glycosylated. Recent studies have revealed several other potential host receptors or factors that can increase or modulate the SARS-CoV-2 infection. Interestingly, most of these molecules bear carbohydrate residues. While glycans acquired by the viruses through the hijacking of the host machinery help the viruses in their infectivity, they also play roles in immune evasion or modulation. Glycans play complex roles in viral pathobiology, both on their own and in association with carrier biomolecules, such as proteins or glycosaminoglycans (GAGs). Understanding these roles in detail can help in developing suitable strategies for prevention and therapy of COVID-19. In this review, we sought to emphasize the interplay of SARS-CoV-2 glycosylated proteins and their host receptors in viral attachment, entry, replication, and infection. Moreover, the implications for future therapeutic interventions targeting these glycosylated biomolecules are also discussed in detail.

Design of the Recombinant Influenza Neuraminidase Antigen Is Crucial for Its Biochemical Properties and Protective Efficacy

Supplementing influenza vaccines with recombinant neuraminidase (rNA) antigens remains a promising approach for improving suboptimal vaccine efficacy. However, correlations among rNA designs, properties, and protection have not been systematically investigated. Here, we performed a comparative analysis of several rNAs produced by the baculovirus/insect cell system. The rNAs were designed with different tetramerization motifs and NA domains from a recent H1N1 vaccine strain (A/Brisbane/02/2018) and compared for enzymatic properties, antigenicity, stability, and protection in mice. We found that the enzymatic properties differ between rNAs containing the NA head domain versus the full ectodomain, the formation of higher-order rNA oligomers is tetramerization domain dependent, whereas the protective efficacy is more contingent on the combination of the tetramerization and NA domains. Following single-dose immunizations, an rNA possessing the full ectodomain and the tetramerization motif from the human vasodilator-stimulated phosphoprotein provided much better protection than an rNA with ∼10-fold more enzymatically active molecules that is comprised of the head domain and the same tetramerization motif. In contrast, these two rNA designs provided comparable protection when the tetramerization motif from the tetrabrachion protein was used instead. These findings demonstrate that individual rNAs should be thoroughly evaluated for vaccine development, as the heterologous domain combination can result in rNAs with similar key attributes that vastly differ in protection. IMPORTANCE For several decades, it has been proposed that influenza vaccines could be supplemented with recombinant neuraminidase (rNA) to improve efficacy. However, some key questions for manufacturing stable and immunogenic rNAs remain to be answered. We show here that the tetramerization motifs and NA domains included in the rNA construct design can have a profound impact on the biochemical, immunogenic, and protective properties. We also show that the single-dose immunization regimen is more informative for assessing the rNA immune response and protective efficacy, which is surprisingly more dependent on the specific combination of NA and tetramerization domains than common attributes for evaluating NA. Our findings may help to optimize the design of rNAs that can be used to improve or develop influenza vaccines.

Antigenic structure of wild poliovirus type 1 strains endemic in Pakistan is highly conserved and completely neutralized by Sabin's Oral Polio Vaccine

BACKGROUND

Elimination of poliovirus in Pakistan and Afghanistan is challenged by notions against the role of oral polio vaccine in eradicating contemporary wild poliovirus strains.

METHODS

1,055 WPV1 strains isolated between 2013-2018 were categorized into 68 antigenic groups and tested for neutralization by OPV derived antibodies. Molecular docking was conducted to determine neutralization efficiency of antibodies against wild poliovirus. The clinical significance of WPV1 variants was assessed to ascertain their role in patient's outcome.

RESULTS

We found that 88% of WPV1 strains isolated from paralytic children belonged to a single antigenic lineage identical to WPV1 strain detected in 1993. WPV1 antigenic variants were effectively neutralized by OPV derived antibodies with geometric mean titers comparable to the neutralization titers found for three strains in OPV (OPV1-3: 7.96-9.149, 95%CI: 6.864-10.171; WPV1 strains: 7.542-8.786, 95%CI: 6.493-9.869). Docking examination underscored a strong antigen-antibody interaction despite variations within the VP1 epitopes. No significant association (p-value = 0.78) of clinical prognosis was inferred among patients infected with antigenically diverse WPV1 strains and patients' outcome including death.

CONCLUSIONS

Our findings substantiate the robustness of OPV to neutralize the contemporary WPV1 strains endemic in Pakistan and Afghanistan. The vaccination coverage must be augmented to achieve eradication early on.

Antibody responses against heterologous A/H5N1 strains for an MF59-adjuvanted cell culture-derived A/H5N1 (aH5N1c) influenza vaccine in healthy pediatric subjects

BACKGROUND

Vaccines are the main prophylactic measure against pandemic influenza. Adjuvanted, cell culture-derived vaccines, which are not subject to limitations of egg-based vaccine production, have the potential to elicit an antibody response against heterologous strains and may be beneficial in the event of an A/H5N1 pandemic.

METHODS

A prespecified exploratory analysis of data from a phase 2, randomized, controlled, observer-blind multicenter trial (NCT01776554) to evaluate the immunogenicity of a MF59-adjuvanted, cell culture-based A/H5N1 influenza vaccine (aH5N1c), containing 7.5 µg hemagglutinin antigen per dose, in subjects 6 months through 17 years of age was conducted. Geometric mean titers (GMT) were determined using hemagglutination inhibition (HI) and microneutralization (MN) assays, and proportions of patients achieving seroconversion, HI and MN titers ≥ 1:40, and a 4-fold increase in MN titers against 5 heterologous strains (influenza A/H5N1 Anhui/2005, Egypt/2010, Hubei/2010, Indonesia/2005, and Vietnam/1203/2004) three weeks after administration of the second dose were assessed.

RESULTS

After the second dose, HI GMTs against heterologous strains increased between 8- and 40-fold, and MN GMTs increased 13- to 160-fold on Day 43 vs Day 1. On Day 43, 32-72% of subjects had HI titers ≥ 1:40 and achieved seroconversion against the heterologous strains. Using the MN assay, 84-100% of subjects had MN titers ≥ 1:40 and 83-100% achieved an at least 4-fold increase in MN titers against the heterologous strains. The highest responses were consistently against A/H5N1 Egypt/2010.

CONCLUSIONS

When given to children aged 6 months through 17 years, aH5N1c resulted in increased immunogenicity from baseline against all 5 heterologous A/H5N1 strains tested, demonstrating the potential of an MF59-adjuvanted, cell-derived A/H5N1 vaccine to provide cross-protection against other A/H5N1 strains (NCT01776554).

A Comprehensive Molecular and Epidemiological Characterization of Influenza Viruses Circulating 2016-2020 in North Macedonia

Influenza viruses know no boundaries, representing an example of rapid virus evolution combined with pressure exerted by the host’s immune system. Seasonal influenza causes 4–50 million symptomatic cases in the EU/EEA each year, with a global death toll reaching 650,000 deaths. That being the case, in 2014 North Macedonia introduced the sentinel surveillance in addition to the existing influenza surveillance in order to obtain more precise data on the burden of disease, circulating viruses and to implement timely preventive measures. The aims of this study were to give a comprehensive virological and epidemiological overview of four influenza seasons (2016–2020), assess the frequency and distribution of influenza circulating in North Macedonia and to carry out molecular and phylogenetic analyses of the hemagglutinin (HA) and neuraminidase (NA) genes of influenza A(H1N1)pdm09, A(H3N2) from ILI and SARI patients. Our results showed that out of 1,632 tested samples, 46.4% were influenza positive, with influenza A(H1N1)pdm09 accounting for the majority of cases (44%), followed by influenza B (32%) and A(H3N2) (17%). By comparing the sentinel surveillance system to the routine surveillance system, we showed that the newly applied system works efficiently and gives great results in the selection of cases. Statistically significant differences (p = < 0.0000001) were observed when comparing the number of reported ILI cases among patients aged 0–4, 5–14, 15–29, and 30–64 years to the reference age group. The phylogenetic analysis of the HA sequences unveiled the resemblance of mutations circulating seasonally worldwide, with a vast majority of circulating viruses belonging to subclade 6B.1A. The PROVEAN analysis showed that the D187A substitution in the receptor binding site (RBS) of the A(H1N1)pdm09 HA has a deleterious effect on the its function. The A(H3N2) viruses fell into the 3C.2a and 3C.3a throughout the analyzed seasons. Molecular characterization revealed that various substitutions in the A(H3N2) viruses gradually replaced the parental variant in subsequent seasons before becoming the dominant variant. With the introduction of sentinel surveillance, accompanied by the advances made in whole-genome sequencing and vaccine therapeutics, public health officials can now modify their approach in disease management and intervene effectively and in a timely manner to prevent major morbidity and mortality from influenza.

mRNA vaccines for infectious diseases: principles, delivery and clinical translation

Over the past several decades, messenger RNA (mRNA) vaccines have progressed from a scepticism-inducing idea to clinical reality. In 2020, the COVID-19 pandemic catalysed the most rapid vaccine development in history, with mRNA vaccines at the forefront of those efforts. Although it is now clear that mRNA vaccines can rapidly and safely protect patients from infectious disease, additional research is required to optimize mRNA design, intracellular delivery and applications beyond SARS-CoV-2 prophylaxis. In this Review, we describe the technologies that underlie mRNA vaccines, with an emphasis on lipid nanoparticles and other non-viral delivery vehicles. We also overview the pipeline of mRNA vaccines against various infectious disease pathogens and discuss key questions for the future application of this breakthrough vaccine platform.

Mutations of 127, 183 and 212 residues on the HA globular head affect the antigenicity, replication and pathogenicity of H9N2 avian influenza virus

H9N2 avian influenza virus (AIV), one of the predominant subtypes devastating the poultry industry, has been circulating widely in the poultry population and causing huge economic losses. In this study, two H9N2 viruses with similar genetic backgrounds but different antigenicity were isolated from a poultry farm, namely A/chicken/Jiangsu/75/2018 (JS/75) and A/chicken/Jiangsu/76/2018 (JS/76). Sequence analysis revealed that their surface genes differed in three amino acid residues (127, 183 and 212) on the head of hemagglutinin (HA). To explore the differences between the two viruses in their biological features, six recombinant viruses, including the wild-type or mutant HA and NA of JS/75 and JS/76 were generated with A/Puerto Rico/8/1934 (PR8) backbone via reverse genetics. The chicken challenge study and HI assay data indicated that r-76/PR8 showed the most obvious antigen escape due to 127 and 183 amino acid substitutions in HA gene. Further studies verified that the 127N site was glycosylated in JS/76 and its mutants. Receptor-binding assays showed that all the recombination viruses were prone to bind the human-like receptors, except for the mutants which glycosylated 127N was deleted. Growth kinetics and mice challenge experiments indicated that 127N-glycosylated viruses showed less replication in A549 cells and lower pathogenicity in mice compared with wild-type viruses. Therefore, the glycosylation site and two amino acid alternations in the HA globular head were responsible for the differences in antigenicity and pathogenicity between the two H9N2 isolates. This study is significant in the research of the antigenic variation and vaccine updates for the H9N2 AIV. Also, highlighted the critical functions of glycosylation in the influenza virus on the pathogenicity against mammals.

A Research and Development (R&D) roadmap for influenza vaccines: Looking toward the future

Improved influenza vaccines are urgently needed to reduce the burden of seasonal influenza and to ensure a rapid and effective public-health response to future influenza pandemics. The Influenza Vaccines Research and Development (R&D) Roadmap (IVR) was created, through an extensive international stakeholder engagement process, to promote influenza vaccine R&D. The roadmap covers a 10-year timeframe and is organized into six sections: virology; immunology; vaccinology for seasonal influenza vaccines; vaccinology for universal influenza vaccines; animal and human influenza virus infection models; and policy, finance, and regulation. Each section identifies barriers, gaps, strategic goals, milestones, and additional R&D priorities germane to that area. The roadmap includes 113 specific R&D milestones, 37 of which have been designated high priority by the IVR expert taskforce. This report summarizes the major issues and priority areas of research outlined in the IVR. By identifying the key issues and steps to address them, the roadmap not only encourages research aimed at new solutions, but also provides guidance on the use of innovative tools to drive breakthroughs in influenza vaccine R&D.

Moving the Needle on Atherosclerotic Cardiovascular Disease and Heart Failure with Influenza Vaccination

PURPOSE OF REVIEW

The interplay between viral respiratory infections and cardiovascular disease has been most comprehensively researched using seasonal and pandemic influenza viruses as case studies. Here, we summarize the latest international observational research and clinical trials that examined the association between influenza, influenza vaccines, and cardiovascular disease, while contextualizing their findings within those of landmark studies.

RECENT FINDINGS

Most recent observational literature found that one in eight adults hospitalized with laboratory-confirmed influenza infection experienced an acute cardiovascular event. The latest meta-analysis of the cardioprotective effects of influenza vaccine found a 25% reduced risk of all-cause death. There are four large cardiovascular outcome trials assessing the cardioprotective effects of different influenza vaccine strategies. Among these, the INVESTED study showed there is no significant difference between the high-dose trivalent and standard-dose quadrivalent influenza vaccines in reducing all-cause mortality or cardiopulmonary hospitalizations in a high-risk patient group with pre-existing cardiovascular disease. Persons with cardiovascular disease represent a high priority group for viral vaccines; hence, using robust evidence to increase vaccine confidence among patients and practitioners is integral as we prepare for a possible influenza resurgence in the coming years.

The Crossroads of Glycoscience, Infection, and Immunology

Advances in experimental capabilities in the glycosciences offer expanding opportunities for discovery in the broad areas of immunology and microbiology. These two disciplines overlap when microbial infection stimulates host immune responses and glycan structures are central in the processes that occur during all such encounters. Microbial glycans mediate host-pathogen interactions by acting as surface receptors or ligands, functioning as virulence factors, impeding host immune responses, or playing other roles in the struggle between host and microbe. In the context of the host, glycosylation drives cell–cell interactions that initiate and regulate the host response and modulates the effects of antibodies and soluble immune mediators. This perspective reports on a workshop organized jointly by the National Institute of Allergy and Infectious Diseases and the National Institute of Dental and Craniofacial Research in May 2020. The conference addressed the use of emerging glycoscience tools and resources to advance investigation of glycans and their roles in microbe-host interactions, immune-mediated diseases, and immune cell recognition and function. Future discoveries in these areas will increase fundamental scientific understanding and have the potential to improve diagnosis and treatment of infections and immune dysregulation.