Influenza B viruses: not to be discounted

Molecular characterisation of influenza B virus from the 2017/18 season in primary models of the human lung reveals improved adaptation to the lower respiratory tract

The 2017/18 influenza season was characterized by unusual high numbers of severe infections and hospitalizations. Instead of influenza A viruses, this season was dominated by infections with influenza B viruses of the Yamagata lineage. While this IBV/Yam dominance was associated with a vaccine mismatch, a contribution of virus intrinsic features to the clinical severity of the infections was speculated. Here, we performed a molecular and phenotypic characterization of three IBV isolates from patients with severe flu symptoms in 2018 and compared it to an IBV/Yam isolate from 2016 using experimental models of increasing complexity, including human lung explants, lung organoids, and alveolar macrophages. Viral genome sequencing revealed the presence of clade but also isolate specific mutations in all viral genes, except NP, M1, and NEP. Comparative replication kinetics in different cell lines provided further evidence for improved replication fitness, tolerance towards higher temperatures, and the development of immune evasion mechanisms by the 2018 IBV isolates. Most importantly, immunohistochemistry of infected human lung explants revealed an impressively altered cell tropism, extending from AT2 to AT1 cells and macrophages. Finally, transcriptomics of infected human lung explants demonstrated significantly reduced amounts of type I and type III IFNs by the 2018 IBV isolate, supporting the existence of additional immune evasion mechanisms. Our results show that the severeness of the 2017/18 Flu season was not only the result of a vaccine mismatch but was also facilitated by improved adaptation of the circulating IBV strains to the environment of the human lower respiratory tract.

PB1-F2 of low pathogenicity H7N7 restricts apoptosis in avian cells

Avian influenza viruses (AIV) pose a continuous challenge to global health and economy. While countermeasures exist to control outbreaks in poultry, the persistent circulation of AIV in wild aquatic and shorebirds presents a significant challenge to effective disease prevention efforts. PB1-F2 is a non-structural protein expressed from a second open reading frame (+1) of the polymerase basic 1 (PB1) segment. The sequence and length of the PB1-F2 protein can vary depending on the host of origin. While avian isolates typically carry full-length PB1-F2, isolates from mammals, often express truncated forms. The selective advantage of the full-length PB1-F2 in avian isolates is not fully understood. Most research on the role of PB1-F2 in influenza virus replication has been conducted in mammalian systems, where PB1-F2 interfered with the host immune response and induced apoptosis. Here, we used Low Pathogenicity (LP) AIV H7N7 expressing full-length PB1-F2 as well as a knockout mutant. We found that the full-length PB1-F2 of LPAIV prolonged survival of infected cells by limiting apoptotic cell death. Furthermore, PB1-F2 knockout LPAIV significantly decreased MHC-I expression on fibroblasts, delayed tissue healing and increased phagocytic uptake of infected cells, whereas LPAIV expressing PB1-F2 has limited effects. These findings indicate that full-length PB1-F2 enables AIV to cause prolonged infections without severely harming the avian host. Our observations may explain maintenance of AIV in the natural bird reservoir in absence of severe clinical signs.

Interferon as an immunoadjuvant to enhance antibodies following influenza B infection and vaccination in ferrets

Despite annual vaccination, influenza B viruses (IBV) continue to cause significant morbidity and mortality in humans. We have found that IBV infection resulted in a weaker innate and adaptive immune response than influenza A viruses (IAV) in ferrets. To understand and overcome the weak immune responses to IBV in ferrets, we administered type-I or type-III interferon (IFN) to ferrets following infection or vaccination and evaluated their effects on the immune response. IFN signaling following viral infection plays an important role in the initial innate immune response and affects subsequent adaptive immune responses. In the respiratory tract, IFN lambda (IFNL) has regulatory effects on adaptive immunity indirectly through thymic stromal lymphopoietin (TSLP), which then acts on immune cells to stimulate the adaptive response. Following IBV infection or vaccination, IFN treatment (IFN-Tx) upregulated gene expression of early inflammatory responses in the upper respiratory tract and robust IFN, TSLP, and inflammatory responses in peripheral blood cells. These responses were sustained following challenge or vaccination in IFN-Tx animals. Serum IFNL and TSLP levels were enhanced in IFN-Tx animals following challenge/rechallenge over mock-Tx; however, this difference was not observed following vaccination. Antibody responses in serum of IFN-Tx animals following IBV infection or vaccination increased more quickly and to higher titers and were sustained longer than mock-Tx animals over 3 months. Following rechallenge of infected animals 3 months post treatment, antibody levels remained higher than mock-Tx. However, IFN-Tx did not have an effect on antibody responses following challenge of vaccinated animals. A strong direct correlation was found between TSLP levels and antibody responses following challenge-rechallenge and vaccination-challenge indicating it as a useful tool for predicting adaptive immune responses following IBV infection or vaccination. The effects of IFN on strengthening both innate and adaptive responses to IBV may aid in development of more effective treatments following infection and improved influenza vaccines.

Prevalence of Influenza B/Yamagata Viruses From Season 2012/2013 to 2021/2022 in Italy as an Indication of a Potential Lineage Extinction

BACKGROUND

Influenza B/Yamagata viruses exhibited weak antigenic selection in recent years, reducing their prevalence over time and requiring no update of the vaccine component since 2015. To date, no B/Yamagata viruses have been isolated or sequenced since March 2020.

METHODS

The antibody prevalence against the current B/Yamagata vaccine strain in Italy was investigated: For each influenza season from 2012/2013 to 2021/2022, 100 human serum samples were tested by haemagglutination inhibition (HAI) assay against the vaccine strain B/Phuket/3073/2013. In addition, the sequences of 156 B/Yamagata strains isolated during the influenza surveillance activities were selected for analysis of the haemagglutinin genome segment.

RESULTS

About 61.9% of the human samples showed HAI antibodies, and 21.7% had protective antibody levels. The prevalence of antibodies at protective levels in the seasons between the isolation of the strain and its inclusion in the vaccine was between 11% and 25%, with no significant changes observed in subsequent years. A significant increase was observed in the 2020/2021 season, in line with the increase in influenza vaccine uptake during the pandemic. Sequence analysis showed that from 2014/2015 season onward, all B/Yamagata strains circulating in Italy were closely related to the B/Phuket/2013 vaccine strain, showing only limited amino acid variation.

CONCLUSIONS

A consistent prevalence of antibodies to the current B/Yamagata vaccine strain in the general population was observed. The prolonged use of a well-matched influenza vaccine and a low antigenic diversity of B/Yamagata viruses may have facilitated a strong reduction in B/Yamagata circulation, potentially contributing to the disappearance of this lineage.

A Single-Component Multilayered Self-Assembling Protein Nanoparticle Vaccine Based on Extracellular Domains of Matrix Protein 2 against Both Influenza A and B

The development of an effective and broadly protective influenza vaccine against circulating and emerging strains remains elusive. In this study, we evaluated a potentially universal influenza vaccine based on single-component self-assembling protein nanoparticles (1c-SApNPs) presenting the conserved matrix protein 2 ectodomain (M2e) from influenza A and B viruses (IAV and IBV, respectively). We previously designed a tandem antigen comprising three IAV M2e domains of human, avian/swine, and human/swine origins (termed M2ex3). The M2ex3-presenting 1c-SApNPs conferred complete protection in mice against sequential lethal challenges with H1N1 and H3N2. To broaden this protection to cover IBVs, we designed a series of antigens incorporating different arrangements of three IAV M2e domains and three copies of IBV M2e. Tandem repeats of IAV and IBV (termed influenza A-B) M2e arrayed on the I3-01v9a 60-mer 1c-SApNP, when formulated with an oil-in-water emulsion adjuvant, generated greater M2e-specific immunogenicity and protective efficacy than the soluble influenza A-B M2e trimer, indicated by higher survival rates and reduced weight loss post-challenge. Importantly, one of the influenza A-B M2e SApNP constructs elicited 100% protection against a lethal influenza A/Puerto Rico/8/1934 (H1N1) challenge in mice and 70% protection against a lethal influenza B/Florida/4/2006 (Yamagata lineage) challenge, the latter of which has not been reported in the literature to date. Our study thus provides a promising M2e-based single-component universal vaccine candidate against the two major types of influenza virus circulating in humans.

A noninferiority randomized open-label pilot study of 3- versus 7-day influenza postexposure prophylaxis with oseltamivir in hospitalized children

Short influenza postexposure prophylaxis (PEP) showed high efficacy in adults, but studies in children are lacking. This randomized open-label pilot trial aimed to verify noninferiority of a 3- versus 7-day prophylaxis with oral oseltamivir in hospitalized children. Influenza contacts were randomized to the 3- or 7-day group and efficacy, relative risk of adverse events (AEs), and the cumulative costs of drugs and AEs management were compared. The intention-to-treat (ITT) analysis included 59 children (n = 28 and n = 31 in the 3- and 7-day group, respectively). The efficacy was 100% (95% CI 87.7-100%) versus 93.6% (95% CI 78.6-99.2%) in the 3- and 7-day group; the differences were statistically insignificant. A per-protocol (PP) analysis including 56 patients (n = 27 and n = 29, respectively) showed 100% (95% CI 87.2-100%) and 93.1% (95% CI 77.2-99.2%) efficacy, respectively, without statistical significance. Differences were within the predefined noninferiority margin with an efficacy difference Δ = 6.45 percentage points (p.p.) with 1-sided 95% CI (- 2.8, - 1.31, p = 0.86; ITT) and Δ = 6.9 p.p. (1-sided 95% CI - 2.83, - 1.27, p = 0.85; PP). Adverse events did not differ significantly, while the cumulative costs of the prophylaxis and AEs management were higher in the 7-day group (median 10.5 euro vs. 4.5 euro, p < 0.01). This pilot study showed the noninferiority of the 3-day versus 7-day PEP, which was associated with lower costs.Trial registration number: NCT04297462, 5th March 2020, restrospectively registered.

Passive immunotherapies for the next influenza pandemic

Influenzavirus is among the most relevant candidates for a next pandemic. We review here the phylogeny of former influenza pandemics, and discuss candidate lineages. After briefly reviewing the other existing antiviral options, we discuss in detail the evidences supporting the efficacy of passive immunotherapies against influenzavirus, with a focus on convalescent plasma.

CD8+ T-cell responses towards conserved influenza B virus epitopes across anatomical sites and age

Influenza B viruses (IBVs) cause substantive morbidity and mortality, and yet immunity towards IBVs remains understudied. CD8+ T-cells provide broadly cross-reactive immunity and alleviate disease severity by recognizing conserved epitopes. Despite the IBV burden, only 18 IBV-specific T-cell epitopes restricted by 5 HLAs have been identified currently. A broader array of conserved IBV T-cell epitopes is needed to develop effective cross-reactive T-cell based IBV vaccines. Here we identify 9 highly conserved IBV CD8+ T-cell epitopes restricted to HLA-B*07:02, HLA-B*08:01 and HLA-B*35:01. Memory IBV-specific tetramer+CD8+ T-cells are present within blood and tissues. Frequencies of IBV-specific CD8+ T-cells decline with age, but maintain a central memory phenotype. HLA-B*07:02 and HLA-B*08:01-restricted NP30-38 epitope-specific T-cells have distinct T-cell receptor repertoires. We provide structural basis for the IBV HLA-B*07:02-restricted NS1196-206 (11-mer) and HLA-B*07:02-restricted NP30-38 epitope presentation. Our study increases the number of IBV CD8+ T-cell epitopes, and defines IBV-specific CD8+ T-cells at cellular and molecular levels, across tissues and age.

Effect of COVID-19 pandemic on influenza; observation of a tertiary level virology laboratory

The lockdown enforced amid the COVID-19 pandemic has affected the occurrence and trends of various respiratory virus infections, with a particular focus on influenza. Our study seeks to analyze the repercussions of the COVID-19 pandemic on the positivity of the influenza virus throughout a 4-year span, encompassing both the pre-COVID-19 era (2018 and 2019) and the COVID-19 period (2020 and 2021). Data collected from patients clinically diagnosed with Influenza-like Illness and Severe Acute Respiratory Illness (SARI) from January 2018 to December 2021 for influenza virus detection were acquired and analyzed through multiplex RT-qPCR. The statistical analysis was conducted using SPSS (Statistical Package for Social Sciences) Version 21.0 Software. A total of 4464 samples were tested over 4 years (2018-2021), with 3201 samples from the pre-COVID era and 1263 samples from the COVID era. Influenza A positivity dropped from 17.7 to 9.57% and Influenza B positivity decreased from 3.74 to 2.61%. Subtyping revealed changes in prevalence for both viruses. Seasonal variations showed more pronounced peaks in the pre-COVID-19 era with reduced activity during lockdown. Influenza A saw a resurgence in August 2021. Throughout the COVID-19 pandemic (2020-2021) SARI cases did not decrease. The positivity rate for Influenza A slightly rose to 7.79% from 4.23% in the COVID period (2020-2021). This increase correlates with heightened hospitalization rates during the pandemic, sparking concerns of potential coinfection with coronavirus and Influenza A. The notable drop in influenza cases in 2020-2021 is likely due to stringent precautions, lockdowns, drug repurposing, and prioritized testing, indicating no reduction in influenza transmission. Increased influenza positivity in SARI patients during COVID-19 highlights a heightened risk of coinfection. Emphasizing solely on COVID-19 may lead to underreporting of other respiratory pathogens, including influenza viruses.

Differential interferon responses to influenza A and B viruses in primary ferret respiratory epithelial cells

Influenza B viruses (IBV) cocirculate with influenza A viruses (IAV) and cause periodic epidemics of disease, yet antibody and cellular responses following IBV infection are less well understood. Using the ferret model for antisera generation for influenza surveillance purposes, IAV resulted in robust antibody responses following infection, whereas IBV required an additional booster dose, over 85% of the time, to generate equivalent antibody titers. In this study, we utilized primary differentiated ferret nasal epithelial cells (FNECs) which were inoculated with IAV and IBV to study differences in innate immune responses which may result in differences in adaptive immune responses in the host. FNECs were inoculated with IAV (H1N1pdm09 and H3N2 subtypes) or IBV (B/Victoria and B/Yamagata lineages) and assessed for 72 h. Cells were analyzed for gene expression by quantitative real-time PCR, and apical and basolateral supernatants were assessed for virus kinetics and interferon (IFN), respectively. Similar virus kinetics were observed with IAV and IBV in FNECs. A comparison of gene expression and protein secretion profiles demonstrated that IBV-inoculated FNEC expressed delayed type-I/II IFN responses and reduced type-III IFN secretion compared to IAV-inoculated cells. Concurrently, gene expression of Thymic Stromal Lymphopoietin (TSLP), a type-III IFN-induced gene that enhances adaptive immune responses, was significantly downregulated in IBV-inoculated FNECs. Significant differences in other proinflammatory and adaptive genes were suppressed and delayed following IBV inoculation. Following IBV infection, ex vivo cell cultures derived from the ferret upper respiratory tract exhibited reduced and delayed innate responses which may contribute to reduced antibody responses in vivo.IMPORTANCEInfluenza B viruses (IBV) represent nearly one-quarter of all human influenza cases and are responsible for significant clinical and socioeconomic impacts but do not pose the same pandemic risks as influenza A viruses (IAV) and have thus received much less attention. IBV accounts for greater severity and deaths in children, and vaccine efficacy remains low. The ferret can be readily infected with human clinical isolates and demonstrates a similar course of disease and immune responses. IBV, however, generates lower antibodies in ferrets than IAV following the challenge. To determine whether differences in initial innate responses following infection may affect the development of robust adaptive immune responses, ferret respiratory tract cells were isolated, infected with IAV/IBV, and compared. Understanding the differences in the initial innate immune responses to IAV and IBV may be important in the development of more effective vaccines and interventions to generate more robust protective immune responses.

Can de-phosphorylation of serine-5 in the C-terminal domain of human polymerase II affect its interaction with the PA C-terminal domain of bat Flu A polymerase?

Influenza viruses depend on the host transcription machinery to create their new progeny viral mRNA. They need the host transcription machinery to hijack the 5'-capped RNA from the host RNAs in order to utilize them to activate their viral transcription. In this study, we computationally regenerated the interaction between 3 heptad repeats, phosphorylated at the fifth serine residue in each repeat, from human polymerase and the CT D of the PA subunit of viral RNA polymerase (Holo 3SEP). We also studied the effect of the de-phosphorylation of the Serine-5 in the middle heptad repeat on the stability of the interaction (Holo 2SEP). The dynamics of the protein association and the heptad repeat in both cases are studied using appropriate in silico tools. This is followed by applying the MM-GBSA method based on relative binding estimation to show the effect of the de-phosphorylation of the middle Serine-5. Results indicate a clear change in total relative binding energy in Holo 2SEP, compared to Holo 3SEP, with no shift in occupied amino acids involved in the interaction in both cases. Knowing that de-phosphorylation of one serine-5 has no significant contribution to the investigated interactions opens the door for further studies to understand the role of the middle heptad serine-5 in these interactions, as its dephosphorylation caused a decrease by ≈13% in the binding affinity values obtained using MM-GBSA. The current in silico study represents a one-step-ahead insight into the RNA-dependent RNA polymerase (RdRP) mechanism that is yet to be verified in the lab.Communicated by Ramaswamy H. Sarma.

Co-evolution of immunity and seasonal influenza viruses

Seasonal influenza viruses cause recurring global epidemics by continually evolving to escape host immunity. The viral constraints and host immune responses that limit and drive the evolution of these viruses are increasingly well understood. However, it remains unclear how most of these advances improve the capacity to reduce the impact of seasonal influenza viruses on human health. In this Review, we synthesize recent progress made in understanding the interplay between the evolution of immunity induced by previous infections or vaccination and the evolution of seasonal influenza viruses driven by the heterogeneous accumulation of antibody-mediated immunity in humans. We discuss the functional constraints that limit the evolution of the viruses, the within-host evolutionary processes that drive the emergence of new virus variants, as well as current and prospective options for influenza virus control, including the viral and immunological barriers that must be overcome to improve the effectiveness of vaccines and antiviral drugs.

Development of an AlphaLISA assay for sensitive and accurate detection of influenza B virus

Objective

Influenza B virus (IBV) is highly contagious, spreads rapidly, and causes seasonal epidemic respiratory disease in the human population, especially in immunocompromised people and young children. Clinical manifestations in this high-risk population are often more severe than in immunocompetent hosts and sometimes atypical. Therefore, rapid, and accurate detection of IBV is important.

Methods

An amplified luminescent proximity homogeneous assay linked immunosorbent assay (AlphaLISA) was developed for detection of IBV by optimizing the ratio of IBV antibody-labeled receptor beads, streptavidin-conjugated donor beads and biotinylated IBV antibody, as well as the optimal temperature and time conditions for incubation. Assay sensitivity, specificity and reproducibility were evaluated. A total of 228 throat swab samples and inactivated influenza B virus were tested by AlphaLISA and lateral flow colloidal gold-based immunoassay (LFIA).

Results

AlphaLISA produced the best results for detection of inactivated influenza B virus when IBV antibody-labeled acceptor beads were 50 μg/ mL, streptavidin-conjugated donor beads were 40 μg/mL, and biotinylated IBV antibody was 0.5 μg/mL at 37°C for 15-10 min. Under these conditions, AlphaLISA had a limit of detection of 0.24 ng/mL for the detection of influenza B nucleoprotein, did not cross react with other common respiratory viruses, and showed good reproducibility with inter-assay coefficient of variation (CV) and intra-assay CV < 5%. The results of 228 clinical throat swab samples showed good agreement between AlphaLISA and LFIA (Kappa = 0.982), and AlphaLISA showed better sensitivity than LFIA for detecting inactivated influenza B virus.

Conclusion

AlphaLISA showed higher sensitivity and throughput in the detection of IBV and can be used for IBV diagnosis and epidemic control.

Burden of Influenza and Respiratory Syncytial Viruses in Suspected COVID-19 Patients: A Cross-Sectional and Meta-Analysis Study

Non-SARS-CoV-2 respiratory viral infections, such as influenza virus (FluV) and human respiratory syncytial virus (RSV), have contributed considerably to the burden of infectious diseases in the non-COVID-19 era. While the rates of co-infection in SARS-CoV-2-positive group (SCPG) patients have been determined, the burden of other respiratory viruses in the SARS-CoV-2-negative group (SCNG) remains unclear. Here, we conducted a cross-sectional study (São José do Rio Preto county, Brazil), and we collected our data using a meta-analysis to evaluate the pooled prevalence of FluV and RSV among SCNG patients. Out of the 901 patients suspected of COVID-19, our molecular results showed positivity of FluV and RSV in the SCNG was 2% (15/733) and 0.27% (2/733), respectively. Co-infection with SARS-CoV-2 and FluV, or RSV, was identified in 1.7% of the patients (3/168). Following our meta-analysis, 28 studies were selected (n = 114,318 suspected COVID-19 patients), with a pooled prevalence of 4% (95% CI: 3-6) for FluV and 2% (95% CI: 1-3) for RSV among SCNG patients were observed. Interestingly, FluV positivity in the SCNG was four times higher (OR = 4, 95% CI: 3.6-5.4, p < 0.01) than in the SCPG. Similarly, RSV positivity was significantly associated with SCNG patients (OR = 2.9, 95% CI: 2-4, p < 0.01). For subgroup analysis, cold-like symptoms, including fever, cough, sore throat, headache, myalgia, diarrhea, and nausea/vomiting, were positively associated (p < 0.05) with the SCPG. In conclusion, these results show that the pooled prevalence of FluV and RSV were significantly higher in the SCNG than in the SCPG during the early phase of the COVID-19 pandemic.

Substitutions near the HA receptor binding site explain the origin and major antigenic change of the B/Victoria and B/Yamagata lineages

Influenza B virus primarily infects humans, causing seasonal epidemics globally. Two antigenic variants-Victoria-like and Yamagata-like-were detected in the 1980s, of which the molecular basis of emergence is still incompletely understood. Here, the antigenic properties of a unique collection of historical virus isolates, sampled from 1962 to 2000 and passaged exclusively in mammalian cells to preserve antigenic properties, were determined with the hemagglutination inhibition assay and an antigenic map was built to quantify and visualize the divergence of the lineages. The antigenic map revealed only three distinct antigenic clusters-Early, Victoria, and Yamagata-with relatively little antigenic diversity in each cluster until 2000. Viruses with Victoria-like antigenic properties emerged around 1972 and diversified subsequently into two genetic lineages. Viruses with Yamagata-like antigenic properties evolved from one lineage and became clearly antigenically distinct from the Victoria-like viruses around 1988. Recombinant mutant viruses were tested to show that insertions and deletions (indels), as observed frequently in influenza B virus hemagglutinin, had little effect on antigenic properties. In contrast, amino-acid substitutions at positions 148, 149, 150, and 203, adjacent to the hemagglutinin receptor binding site, determined the main antigenic differences between the Early, Victoria-like, and Yamagata-like viruses. Surprisingly, substitutions at two of the four positions reverted in recent viruses of the Victoria lineage, resulting in antigenic properties similar to viruses circulating ∼50 y earlier. These data shed light on the antigenic diversification of influenza viruses and suggest there may be limits to the antigenic evolution of influenza B virus.

Association Between Baloxavir Marboxil Prescription for Children with Influenza B Infections and Short-Term Healthcare Consumption in Japan During the 2018-2019 Influenza Season

BACKGROUND

Baloxavir marboxil is an anti-influenza medication that was newly introduced into clinical practice in 2018. Baloxavir might be more beneficial than neuraminidase inhibitors (NAIs), as suggested by a subgroup analysis of a clinical trial. Although the association between baloxavir prescription and healthcare use pertains mainly to influenza A, few studies have investigated the association in influenza B.

METHODS

We evaluated the healthcare utilization of children (0-15 years old) treated with either baloxavir or NAIs between December 2018 and May 2019 using claims records in Japan. The primary endpoint was the composite of medical resource utilization, including hospitalization, antibiotic use, laboratory tests, radiological images, and fluid replacement therapy, over 1-9 days after antiviral prescription. Secondary outcomes representing each single outcome in the composite were examined. Subgroup analyses comparing baloxavir with each NAI were also performed.

RESULTS

Of 4490 patients with influenza B who received antiviral treatment, 51.6% were male, and the median age was 8 years old. Baloxavir was prescribed for 29.4% of the population, and NAIs were prescribed for 70.6%. In the total cohort, 49.3% of patients had any comorbidity related to complicated influenza infection. Concerning the composite endpoint, baloxavir prescription was not associated with a risk of subsequent medical resource use (adjusted odds ratio 1.11; 95% confidence interval 0.90-1.38; P = 0.34). Secondary outcomes and subgroup analyses showed similar results to the primary outcome.

CONCLUSIONS

In a single-year comparative study in Japan, baloxavir prescription for influenza B was not associated with less healthcare consumption than NAIs within 9 days of treatment.

Cross-Protection Induced by Virus-like Particles Derived from the Influenza B Virus

The mismatch between the circulating influenza B virus (IBV) and the vaccine strain contributes to the rapid emergence of IBV infection cases throughout the globe, which necessitates the development of effective vaccines conferring broad protection. Here, we generated influenza B virus-like particle (VLP) vaccines expressing hemagglutinin, neuraminidase, or both antigens derived from the influenza B virus (B/Washington/02/2019 (B/Victoria lineage)-like virus, B/Phuket/3073/2013 (B/Yamagata lineage)-like virus. We found that irrespective of the derived antigen lineage, immunizing mice with the IBV VLPs significantly reduced lung viral loads, minimized bodyweight loss, and ensured 100% survival upon Victoria lineage virus B/Colorado/06/2017 challenge infection. These results were closely correlated with the vaccine-induced antibody responses and HI titer in sera, IgG, IgA antibody responses, CD4+ and CD8+ T cell responses, germinal center B cell responses, and inflammatory cytokine responses in the lungs. We conclude that hemagglutinin, neuraminidase, or both antigen-expressing VLPs derived from these influenza B viruses that were circulating during the 2020/21 season provide cross-protections against mismatched Victoria lineage virus (B/Colorado/06/2017) challenge infections.

Universal antibody targeting the highly conserved fusion peptide provides cross-protection in mice

Influenza is a major public health concern causing millions of hospitalizations every year. The current vaccines need annual updating based on prediction of likely strains in the upcoming season. However, mismatches between vaccines and the actual circulating viruses can occur, reducing vaccine effectiveness significantly because of the remarkably high rate of mutation in the viral glycoprotein, hemagglutinin (HA). Clearly, it would be of great interest to determine the potential role of universally conserved epitopes in inducing protective immunity. Here, an antibody against the 14-aa fusion peptide sequence at the N-terminus of the HA2 subunit (Uni-1) was investigated for its ability to elicit antibody-dependent cellular cytotoxicity (ADCC) in vitro and cross-protection against lethal infection in animals. Uni-1, known to neutralize influenza type A (IAV) in vitro, was found to induce strong ADCC against diverse influenza viruses, including human and avian IAVs and both lineages of type B (IBV). The ADCC effects against human IAVs by Uni-1 was comparable to ADCC induced by well-characterized antibodies, F10 and FI6V3. Importantly, mice treated with Uni-1 were protected against lethal challenge of IAV and IBV. These results revealed the versatile effector functions of this universal antibody against markedly diverse strains of both IAV and IBV.

The fusion peptide is the only universally conserved epitope in both IAV and IBV

Mono-specific universal antibody induces strong ADCC against human and avian IAV

Mono-specific universal antibody induces strong ADCC against IBV from both genetic lineages of IBV

The antibody has bi-functional effector functions against several influenza viruses

Influenza B: Prospects for the Development of Cross-Protective Vaccines

In this review, we analyze the epidemiological and ecological features of influenza B, one of the most common and severe respiratory infections. The review presents various strategies for cross-protective influenza B vaccine development, including recombinant viruses, virus-like particles, and recombinant proteins. We provide an overview of viral proteins as cross-protective vaccine targets, along with other updated broadly protective vaccine strategies. The importance of developing such vaccines lies not only in influenza B prevention, but also in the very attractive prospect of eradicating the influenza B virus in the human population.

Epidemiological and Clinical Characteristics of Influenza Outbreaks Among Children in Chongqing, China

Influenza is a global serious public health threat. Seasonal influenza among children in Chongqing has been a heavy health burden. To date, few studies have examined the spatial and temporal characteristics of influenza. This research sheds new light on correlating them with influenza outbreaks with data of over 5 years (2014–2018). All cluster outbreaks among preschool and school-age children reported in Chongqing were collected through the Public Health Emergency Management Information System. The demographical, epidemiological, and clinical data of the cases were analyzed. From 2014 to 2018, a total of 111 preschool- and school-based influenza-like illness outbreaks involving 3,549 cases were identified. Several clinical symptoms that were analyzed in this study showed significant contrast between influenza A and B. Spatial autocorrelation analysis over the 5-year data detected Xiushan district being the most likely cluster. The exploration of the spatial distribution and clinical characteristics of influenza cluster of children in Chongqing could help the effective implementation of health policies. Future studies should be conducted to monitor the outbreaks of influenza among children.

Development of functional antibodies against influenza B virus by activation-induced cytidine deaminase in hybridoma cells

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Class-switch recombination was mimicked in hybridomas by controllable expression of activation-induced cytidine deaminase.

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IgG antibodies were generated through this system in an anti-Flu B IgM hybridoma 7G1.

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IgG1 and IgG2a subtypes of 7G1 present improved antiviral activity in vitro and in vivo.

Development of a Mouse Model to Explore CD4 T Cell Specificity, Phenotype, and Recruitment to the Lung after Influenza B Infection

The adaptive T cell response to influenza B virus is understudied, relative to influenza A virus, for which there has been considerable attention and progress for many decades. Here, we have developed and utilized the C57BL/6 mouse model of intranasal infection with influenza B (B/Brisbane/60/2008) virus and, using an iterative peptide discovery strategy, have identified a series of robustly elicited individual CD4 T cell peptide specificities. The CD4 T cell repertoire encompassed at least eleven major epitopes distributed across hemagglutinin, nucleoprotein, neuraminidase, and non-structural protein 1 and are readily detected in the draining lymph node, spleen, and lung. Within the lung, the CD4 T cells are localized to both lung vasculature and tissue but are highly enriched in the lung tissue after infection. When studied by flow cytometry and MHC class II: peptide tetramers, CD4 T cells express prototypical markers of tissue residency including CD69, CD103, and high surface levels of CD11a. Collectively, our studies will enable more sophisticated analyses of influenza B virus infection, where the fate and function of the influenza B-specific CD4 T cells elicited by infection and vaccination can be studied as well as the impact of anti-viral reagents and candidate vaccines on the abundance, functionality, and localization of the elicited CD4 T cells.

Maximum antigen diversification in a lyme bacterial population and evolutionary strategies to overcome pathogen diversity

Natural populations of pathogens and their hosts are engaged in an arms race in which the pathogens diversify to escape host immunity while the hosts evolve novel immunity. This co-evolutionary process poses a fundamental challenge to the development of broadly effective vaccines and diagnostics against a diversifying pathogen. Based on surveys of natural allele frequencies and experimental immunization of mice, we show high antigenic specificities of natural variants of the outer surface protein C (OspC), a dominant antigen of a Lyme Disease-causing bacterium (Borrelia burgdorferi). To overcome the challenge of OspC antigenic diversity to clinical development of preventive measures, we implemented a number of evolution-informed strategies to broaden OspC antigenic reactivity. In particular, the centroid algorithm-a genetic algorithm to generate sequences that minimize amino-acid differences with natural variants-generated synthetic OspC analogs with the greatest promise as diagnostic and vaccine candidates against diverse Lyme pathogen strains co-existing in the Northeast United States. Mechanistically, we propose a model of maximum antigen diversification (MAD) mediated by amino-acid variations distributed across the hypervariable regions on the OspC molecule. Under the MAD hypothesis, evolutionary centroids display broad cross-reactivity by occupying the central void in the antigenic space excavated by diversifying natural variants. In contrast to vaccine designs based on concatenated epitopes, the evolutionary algorithms generate analogs of natural antigens and are automated. The novel centroid algorithm and the evolutionary antigen designs based on consensus and ancestral sequences have broad implications for combating diversifying pathogens driven by pathogen-host co-evolution.

Influenza B Lineages Have More in Common Than Meets the Eye. Trivalent Influenza Vaccines Trigger Heterotypic Antibodies Against Both Influenza B Viruses

Influenza B is accountable for an important burden during flu epidemics, causing special impact in children and the elderly. Vaccination is the best approach to address influenza infections. However, one of the main problems of this virus is that two different lineages circulate together, Victoria and Yamagata; and trivalent vaccines, that only contain one of these lineages, are still in use. For that reason, if during an epidemic, the lineage not included in the vaccine predominates, a mismatch would occur, and the vaccine effectiveness will be very poor. In this work, we evaluated the cross-protection given by the trivalent Influenza vaccine and compared serological profiles based on age, sex, and the type of vaccine used. We performed a retrospective analysis of serum samples obtained before and after seasonal influenza vaccination during 20 seasons (1998–2018). The results showed that heterotypic reactivity between both influenza B lineages is common, but always lower than the homologous response. Age is a relevant factor for this cross-reactivity between both lineages, while the sex and the type of vaccine not. Vaccination with trivalent influenza vaccines elicits cross-reactive antibodies against both lineages, however, this response might not be enough to provide an appropriate serological protection in case of mismatch.

Evolutionary perspectives and adaptation dynamics of human seasonal influenza viruses from 2009 to 2019: An insight from codon usage

The annually recurrent seasonal influenza viruses, namely, influenza A viruses (H1N1/pdm2009 and H3N2) and influenza B viruses, contribute substantially to human disease burden. Elucidation of host adaptation, population dynamics and evolutionary patterns of these viruses contribute to better control of current epidemic situation and bolster efforts towards pandemic preparedness. Present study has been addressed at unraveling the signatures of codon usage and dinucleotide distribution of these seasonal influenza viruses associating with their fitness and ongoing adaptive evolution in human population. Thorough analysis of codon usage adaptation revealed that H3N2 has been exhibited best adapted to human cellular system, which correlate with its highest epidemic intensity as compared with the other seasonal influenza viruses. CpG dinucleotide was found to be strongly avoided among the seasonal influenza viruses with more restraint among influenza B viruses than influenza A viruses, and might be accounted to the strategy of the viral pathogens in evading human immune signals. Dynamic scenes of ongoing evolution in codon usage and elimination of CpG motif among the viruses, which correlate with their distinct host adaption state, signifying the marked impact of selective force operational on the viral genomes, aimed at proficient circulation, enhanced fitness and successful infective manifestations in humans.

Baloxavir Treatment Delays Influenza B Virus Transmission in Ferrets and Results in Limited Generation of Drug-Resistant Variants

Clinical efficacy of the influenza antiviral baloxavir marboxil (baloxavir) is compromised by treatment-emergent variants harboring a polymerase acidic protein I38T (isoleucine-38-threonine) substitution. However, the fitness of I38T-containing influenza B viruses (IBVs) remains inadequately defined. After the pharmacokinetics of the compound were confirmed in ferrets, animals were injected subcutaneously with 8 mg/kg of baloxavir acid (BXA) at 24 h postinoculation with recombinant BXA-sensitive (BXA-Sen, I38) or BXA-resistant (BXA-Res, I38T) B/Brisbane/60/2008 (Victoria lineage) virus. BXA treatment of donor ferrets reduced virus replication and delayed transmission of the BXA-Sen but not the BXA-Res IBV. The I38 genotype remained dominant in the BXA-Sen-infected animals, even with BXA treatment. In competitive-mixture experiments, no transmission to aerosol contacts was seen from BXA-treated donors coinfected with the BXA-Sen and BXA-Res B/Brisbane/60/2008 viruses. However, in parallel mixed infections with the B/Phuket/3073/2013 (Yamagata lineage) virus background, BXA treatment failed to block airborne transmission of the BXA-Res virus, and the I38T genotype generally predominated. Therefore, the relative fitness of BXA-Res IBVs is complex and dependent on the virus backbone and within-host virus competition. BXA treatment of single-virus-infected ferrets hampers aerosol transmission of the BXA-Sen virus and does not readily generate BXA-Res variants, whereas mixed infections may result in propagation of BXA-Res IBVs of the Yamagata lineage. Our findings confirm the antiviral potency of baloxavir against IBVs, while supporting optimization of the dosing regimen to maximize clinical benefit.

Impact of coinfection status and comorbidity on disease severity in adult emergency department patients with influenza B

Background

Influenza B accounts for approximately one fourth of the seasonal influenza burden. However, research on the importance of influenza B has received less attention compared to influenza A. We sought to describe the association of both coinfections and comorbidities with disease severity among adults presenting to emergency departments (ED) with influenza B.

Methods

Nasopharyngeal samples from patients found to be influenza B positive in four US and three Taiwanese ED over four consecutive influenza seasons (2014–2018) were tested for coinfections with the ePlex RP RUO panel. Multivariable logistic regressions were fitted to model adjusted odds ratios (aOR) for two severity outcomes separately: hospitalization and pneumonia diagnosis. Adjusting for demographic factors, underlying health conditions, and the National Early Warning Score (NEWS), we estimated the association of upper respiratory coinfections and comorbidity with disease severity (including hospitalization or pneumonia).

Results

Amongst all influenza B positive individuals (n = 446), presence of another upper respiratory pathogen was associated with an increased likelihood of hospitalization (aOR = 2.99 [95% confidence interval (95% CI): 1.14–7.85, p = 0.026]) and pneumonia (aOR = 2.27 [95% CI: 1.25–4.09, p = 0.007]). Chronic lung diseases (CLD) were the strongest predictor for hospitalization (aOR = 3.43 [95% CI: 2.98–3.95, p < 0.001]), but not for pneumonia (aOR = 1.73 [95% CI: 0.80–3.78, p = 0.166]).

Conclusion

Amongst ED patients infected with influenza B, the presence of other upper respiratory pathogens was independently associated with both hospitalization and pneumonia; presence of CLD was also associated with hospitalization. These findings may be informative for ED clinician's in managing patients infected with influenza B.

Sialic Acids as Receptors for Pathogens

Carbohydrates have long been known to mediate intracellular interactions, whether within one organism or between different organisms. Sialic acids (Sias) are carbohydrates that usually occupy the terminal positions in longer carbohydrate chains, which makes them common recognition targets mediating these interactions. In this review, we summarize the knowledge about animal disease-causing agents such as viruses, bacteria and protozoa (including the malaria parasite Plasmodium falciparum) in which Sias play a role in infection biology. While Sias may promote binding of, e.g., influenza viruses and SV40, they act as decoys for betacoronaviruses. The presence of two common forms of Sias, Neu5Ac and Neu5Gc, is species-specific, and in humans, the enzyme converting Neu5Ac to Neu5Gc (CMAH, CMP-Neu5Ac hydroxylase) is lost, most likely due to adaptation to pathogen regimes; we discuss the research about the influence of malaria on this trait. In addition, we present data suggesting the CMAH gene was probably present in the ancestor of animals, shedding light on its glycobiology. We predict that a better understanding of the role of Sias in disease vectors would lead to more effective clinical interventions.

New 2013 incidence peak in childhood narcolepsy: more than vaccination?

Increased incidence rates of narcolepsy type-1 (NT1) have been reported worldwide after the 2009-2010 H1N1 influenza pandemic (pH1N1). While some European countries found an association between the NT1 incidence increase and the H1N1 vaccination Pandemrix, reports from Asian countries suggested the H1N1 virus itself to be linked to the increased NT1 incidence. Using robust data-driven modeling approaches, that is, locally estimated scatterplot smoothing methods, we analyzed the number of de novo NT1 cases (n = 508) in the last two decades using the European Narcolepsy Network database. We confirmed the peak of NT1 incidence in 2010, that is, 2.54-fold (95% confidence interval [CI]: [2.11, 3.19]) increase in NT1 onset following 2009-2010 pH1N1. This peak in 2010 was found in both childhood NT1 (2.75-fold increase, 95% CI: [1.95, 4.69]) and adulthood NT1 (2.43-fold increase, 95% CI: [2.05, 2.97]). In addition, we identified a new peak in 2013 that is age-specific for children/adolescents (i.e. 2.09-fold increase, 95% CI: [1.52, 3.32]). Most of these children/adolescents were HLA DQB1*06:02 positive and showed a subacute disease onset consistent with an immune-mediated type of narcolepsy. The new 2013 incidence peak is likely not related to Pandemrix as it was not used after 2010. Our results suggest that the increased NT1 incidence after 2009-2010 pH1N1 is not unique and our study provides an opportunity to develop new hypotheses, for example, considering other (influenza) viruses or epidemiological events to further investigate the pathophysiology of immune-mediated narcolepsy.

The Intersection of Age and Influenza Severity: Utility of Ferrets for Dissecting the Age-Dependent Immune Responses and Relevance to Age-Specific Vaccine Development

Many factors impact the host response to influenza virus infection and vaccination. Ferrets have been an indispensable reagent for influenza virus research for almost one hundred years. One of the most significant and well-known factors affecting human disease after infection is host age. Another significant factor is the virus, as strain-specific disease severity is well known. Studying age-related impacts on viral infection and vaccination outcomes requires an animal model that reflects both the physiological and immunological changes that occur with human aging, and sensitivity to differentially virulent influenza viruses. The ferret is uniquely susceptible to a plethora of influenza viruses impacting humans and has proven extremely useful in studying the clinical and immunological pictures of influenza virus infection. Moreover, ferrets developmentally have several of the age-related physiological changes that occur in humans throughout infancy, adulthood, old age, and pregnancy. In this review, we discuss ferret susceptibility to influenza viruses, summarize previous influenza studies using ferrets as models of age, and finally, highlight the application of ferret age models in the pursuit of prophylactic and therapeutic agents to address age-related influenza disease severity.

Influenza vaccination and healthcare workers: barriers and predisposing factors

BACKGROUND AND AIM OF THE WORK

Influenza is a disease that affects a large part of the world's population annually, with major health, social and economic impacts. Active immunisation practices have always been recommended to counter influenza, especially for people at risk. The recommendations of major health agencies strongly advise influenza vaccination for all healthcare workers, mostly for those in contact with at-risk or immunocompromised individuals. Yet, the influenza vaccination coverage among healthcare workers remains rather low worldwide. This review explore barriers and the facilitators of health care professional toward influenza's vaccination.

METHODS

Narrative review  consulting the databases: PubMed, CINAHL by combining keywords health care worker, flu, influenza, vaccination, barrier, resistence, hesitangy, between November 2019 and February 2020 Results. From the 1031 records initially, twenty-two primary studies were included in this narrative review. Our results show that the identified facilitators are: desire for self-protection, protection for loved ones and community. Instead, the barriers to vaccination identified are: fear of contracting influenza from the vaccination itself; not considering themselves at risk; to believing believe that their immune system is capable of managing a trivial disease; disease considered trivial, laziness; false beliefs.

DISCUSSION AND CONCLUSION

Adherence rate on influenza vaccination among health professionals is quite low. The interventions that make it "complex and traceable" flu vaccination refusal increase adherence to this type of vaccination. The results show that current vaccination campaigns do not increase the rate of adherence by healthcare workers. Identifying the predisposing factors and barriers to such vaccination can help to create, develop and test targeted educational programmes.

Influenza B viruses: underestimated and overlooked

Influenza B viruses circulate globally every year causing respiratory disease with significant clinical and socio-economic impacts. IBV are considered exclusive human pathogens with no established animal reservoirs, which suggests with concerted effort it may be possible to eradicate this virus from human circulation. However, this requires a deeper understanding of IBV virology and immunology and the design of vaccines that induce universal immunity to antigenic variants of IBV.

Altered NKp46 Recognition and Elimination of Influenza B Viruses

Every year, millions of people worldwide are infected with influenza, causing enormous health and economic problems. The most common type of influenza is influenza A. It is known that Natural Killer (NK) cells play an important role in controlling influenza A infection, mostly through the recognition of the viral protein hemagglutinin (HA) by the activating receptor, NKp46. In contrast, little is known regarding NK cell recognition of influenza B viruses, even though they are responsible for a third of all pediatric influenza deaths and are therefore included in the seasonal vaccine each year. Here we show that NKp46 also recognizes influenza B viruses. We show that NKp46 binds the HA protein of influenza B in a sialic acid-dependent manner, and identified the glycosylated residue in NKp46, which is critical for this interaction. We discovered that this interaction has a binding affinity approximately seven times lower than NKp46 binding of influenza A’s HA. Finally, we demonstrated, using mice deficient for the mouse orthologue of NKp46, named NCR1, that NKp46 is not important for influenza B elimination. These findings enable us to better understand the interactions between the different influenza viruses and NK cells that are known to be crucial for viral elimination.

Burden of influenza B virus infection and considerations for clinical management

Influenza B viruses cause significant morbidity and mortality, particularly in children, but the awareness of their impact is often less than influenza A viruses partly due to their lack of pandemic potential. Here, we summarise the biology, epidemiology and disease burden of influenza B, and review existing data on available antivirals for its management. There has long been uncertainty surrounding the clinical efficacy of neuraminidase inhibitors (NAIs) for influenza B treatment. In this article, we bring together the existing data on NAIs and discuss these alongside recent large randomised controlled trial data for the new polymerase inhibitor baloxavir in high-risk influenza B patients. Finally, we offer considerations for the clinical management of influenza B, with a focus on children and high-risk patients where disease burden is highest.

Airway Delivery of Anti-influenza Monoclonal Antibodies Results in Enhanced Antiviral Activities and Enables Broad-Coverage Combination Therapies

Influenza causes widespread illness in humans and can result in morbidity and death, especially in the very young and elderly populations. Because influenza vaccination can be poorly effective some years, and the immune systems of the most susceptible populations are often compromised, passive immunization treatments using broadly neutralizing antibodies is a promising therapeutic approach. However, large amounts of a single antibody are required for effectiveness when delivered through systemic administration (typically intravenous infusion), precluding the feasible dosing of antibody combinations via this route. The significance of our research is the demonstration that effective therapeutic treatments of multiple relevant influenza types (H1N1, H3N2, and B) can be achieved by airway administration of a single combination of relatively small amounts of three anti-influenza antibodies. This advance exploits the discovery that airway delivery is a more potent way of administering anti-influenza antibodies compared to systemic delivery, making this a feasible and cost-effective therapeutic approach.

Effective and reliable anti-influenza treatments are acutely needed and passive immunizations using broadly neutralizing anti-influenza monoclonal antibodies (bNAbs) are a promising emerging approach. Because influenza infections are initiated in and localized to the pulmonary tract, and newly formed viral particles egress from the apical side of the lung epithelium, we compared the effectiveness of hemagglutinin (HA) stalk-binding bNAbs administered through the airway (intranasal or via nebulization) versus the systemic route (intraperitoneal or intravenous). Airway deliveries of various bNAbs were 10- to 50-fold more effective than systemic deliveries of the same bNAbs in treating H1N1, H3N2, B/Victoria-, and B/Yamagata-lineage influenza viral infections in mouse models. The potency of airway-delivered anti-HA bNAbs was highly dependent on antiviral neutralization activity, with little dependence on the effector function of the antibody. In contrast, the effectiveness of systemically delivered anti-HA bNAbs was not dependent on antiviral neutralization, but critically dependent on antibody effector functions. Concurrent administration of a neutralizing/effector function-positive bNAb via the airway and systemic routes showed increased effectiveness. The small amount of airway-delivered bNAbs needed for effective influenza treatment creates the opportunity to combine potent bNAbs with different anti-influenza specificities to generate a cost-effective antiviral therapy that provides broad coverage against all circulating influenza strains infecting humans. A 3 mg/kg dose of the novel triple antibody combination CF-404 (i.e., 1 mg/kg of each component bNAb) delivered to the airway was shown to effectively prevent weight loss and death in mice challenged with ten 50% lethal dose (LD₅₀) inoculums of either H1N1, H3N2, B/Victoria-lineage, or B/Yamagata-lineage influenza viruses.

IMPORTANCE Influenza causes widespread illness in humans and can result in morbidity and death, especially in the very young and elderly populations. Because influenza vaccination can be poorly effective some years, and the immune systems of the most susceptible populations are often compromised, passive immunization treatments using broadly neutralizing antibodies is a promising therapeutic approach. However, large amounts of a single antibody are required for effectiveness when delivered through systemic administration (typically intravenous infusion), precluding the feasible dosing of antibody combinations via this route. The significance of our research is the demonstration that effective therapeutic treatments of multiple relevant influenza types (H1N1, H3N2, and B) can be achieved by airway administration of a single combination of relatively small amounts of three anti-influenza antibodies. This advance exploits the discovery that airway delivery is a more potent way of administering anti-influenza antibodies compared to systemic delivery, making this a feasible and cost-effective therapeutic approach.

In Vivo Assessment of Antibody-Dependent Enhancement of Influenza B Infection

A theoretical safety concern proposed in the influenza literature is that therapeutic antiviral antibodies could have the potential for antibody-dependent enhancement (ADE) of infection and disease. ADE may occur when virus-specific antibodies at subtherapeutic, nonneutralizing concentrations facilitate virus uptake and, in some cases, enhance replication, which can lead to an exacerbation of virus-mediated disease. Alternatively, ADE may occur due to antibody-dependent complement activation exacerbating virus-mediated disease in the absence of increased replication. As a result of this theoretical safety concern, safety assessment of anti-influenza antibodies may include an in vivo evaluation of ADE of infection and/or disease. These studies were conducted to investigate the potential of MHAB5553A, a broadly specific, neutralizing therapeutic anti-influenza B antibody, to elicit ADE of infection and disease in mouse models of influenza B infection. In parallel studies, female DBA/2J mice were infected with either influenza B/Victoria/504/2000 or influenza B/Brisbane/60/2008 representing distinct lineages. Assessment of ADE was based on an integration of results from multiple endpoints, including infectious lung viral titers and genomes, body weight, mortality, lung weight, and histopathology. In these studies, the high dose of 15 mg/kg MHAB5553A resulted in substantial attenuation of influenza pneumonia, with more modest effects at 1.5 mg/kg; whereas MHAB5553A treatment at 0.15 or 0.015 mg/kg was generally comparable to vehicle-treated controls. Our results demonstrate that MHAB5553A across a broad range of doses did not enhance primary influenza B infection or disease in this model, and represent a nonclinical de-risking of the ADE potential with this antibody.

Immunogenicity and safety of a quadrivalent inactivated influenza vaccine in healthy subjects aged 3 to 17 years old: A phase III, open label, single-arm study

BACKGROUND

Quadrivalent influenza vaccines are particularly valuable during seasons in which a mismatch occurs between the predicted influenza B lineage for the trivalent influenza vaccine and the circulating strain. This study evaluated the immunogenicity and safety of a quadrivalent inactivated influenza vaccine AdimFlu-S manufactured in Taiwan for the 2016-2017 influenza season in healthy children.

METHODS

A total of 174 healthy children aged 3 to 17 years old were separated into 3 groups (Group A: 3-8 years old, vaccine naïve; Group B: 3-8 years old, vaccine non-naïve; Group C: 9-17 years old, any vaccine status). Sera was collected pre and post vaccination for each participant. A hemagglutination inhibition (HAI) assay was utilized to calculate geometric mean titer (GMT), seroprotection rate, and seroconversion rate.

RESULTS

All enrolled participants completed the study. For the four vaccine strains four weeks after the last vaccination, geometric mean titer ratios (GMTRs) were between 2.9 and 20.9, seroconversion rates were between 42.9% and 90.9%, and seroprotection rates were all above 96.4%. This achieved all immunogenicity endpoints and fulfilled the criteria of the European Medical Agency's Committee for Medicinal Products for Human Use (CHMP). No serious adverse events (AEs) were reported during the follow-up period of 6 months.

CONCLUSION

This quadrivalent influenza vaccine is demonstrated to be well tolerated and displays robust immunogenicity for each influenza strain. This could potentially improve protection against the antigenically distinct B/Yamagata and B/Victoria lineages.

Immune Pressure on Polymorphous Influenza B Populations Results in Diverse Hemagglutinin Escape Mutants and Lineage Switching

Mutations arise in the genomes of progeny viruses during infection. Mutations that occur in epitopes targeted by host antibodies allow the progeny virus to escape the host adaptive, B-cell mediated antibody immune response. Major epitopes have been identified in influenza B virus (IBV) hemagglutinin (HA) protein. However, IBV strains maintain a seasonal presence in the human population and changes in IBV genomes in response to immune pressure are not well characterized. There are two lineages of IBV that have circulated in the human population since the 1980s, B-Victoria and B-Yamagata. It is hypothesized that early exposure to one influenza subtype leads to immunodominance. Subsequent seasonal vaccination or exposure to new subtypes may modify subsequent immune responses, which, in turn, results in selection of escape mutations in the viral genome. Here we show that while some mutations do occur in known epitopes suggesting antibody escape, many mutations occur in other parts of the HA protein. Analysis of mutations outside of the known epitopes revealed that these mutations occurred at the same amino acid position in viruses from each of the two IBV lineages. Interestingly, where the amino acid sequence differed between viruses from each lineage, reciprocal amino acid changes were observed. That is, the virus from the Yamagata lineage become more like the Victoria lineage virus and vice versa. Our results suggest that some IBV HA sequences are constrained to specific amino acid codons when viruses are cultured in the presence of antibodies. Some changes to the known antigenic regions may also be restricted in a lineage-dependent manner. Questions remain regarding the mechanisms underlying these results. The presence of amino acid residues that are constrained within the HA may provide a new target for universal vaccines for IBV.

The human antibody response to influenza A virus infection and vaccination

The adaptive immune response to influenza virus infection is multifaceted and complex, involving antibody and cellular responses at both systemic and mucosal levels. Immune responses to natural infection with influenza virus in humans are relatively broad and long-lived, but influenza viruses can escape from these responses over time owing to their high mutation rates and antigenic flexibility. Vaccines are the best available countermeasure against infection, but vaccine effectiveness is low compared with other viral vaccines, and the induced immune response is narrow and short-lived. Furthermore, inactivated influenza virus vaccines focus on the induction of systemic IgG responses but do not effectively induce mucosal IgA responses. Here, I review the differences between natural infection and vaccination in terms of the antibody responses they induce and how these responses protect against future infection. A better understanding of how natural infection induces broad and long-lived immune responses will be key to developing next-generation influenza virus vaccines.

Influenza A and B in a cohort of outpatient children and adolescent with influenza like-illness during two consecutive influenza seasons

INTRODUCTION

Influenza is an important cause of morbimortality worldwide. Although people at the extremes of age have a greater risk of complications, influenza has been more frequently investigated in the elderly than in children, and inpatients than outpatients. Yearly vaccination with trivalent or quadrivalent vaccines is the main strategy to control influenza.

OBJECTIVES

Determine the clinical and molecular characteristics of influenza A and B infections in children and adolescents with influenza-like illness (ILI).

METHODS

A cohort of outpatient children and adolescents with ILI was followed for 20 months. Influenza was diagnosed with commercial multiplex PCR platforms.

RESULTS

179 patients had 277 episodes of ILI, being 79 episodes of influenza A and 20 episodes of influenza B. Influenza A and B cases were mild and had similar presentation. Phylogenetic tree of influenza B viruses showed that 91.6% belonged to the B/Yamagata lineage, which is not included in trivalent vaccines.

CONCLUSIONS

Influenza A and B are often detected in children and adolescents with ILI episodes, with similar and mild presentation in outpatients. The mismatch between the circulating influenza viruses and the trivalent vaccine offered in Brazil may have contributed to the high frequency of influenza A and B in this population.

Influenza B viruses from different genetic backgrounds are variably impaired by neuraminidase inhibitor resistance-associated substitutions

Identifying evolutionary routes to antiviral resistance among influenza viruses informs molecular-based resistance surveillance and clinical decisions. To improve antiviral management and understand whether clinically identified neuraminidase (NA) inhibitor (NAI) resistance-associated markers affect influenza B viruses of the Victoria- or Yamagata-lineages differentially, we generated a panel of NAI-resistant viruses (carrying E105K, G145E, R150K, D197N, I221 L/N/T/V, H273Y, N294S, or G407S substitutions; B numbering) in B/Brisbane/60/2008 (BR/08) and B/Phuket/3073/2013 (PH/13). In both backgrounds, I221 L/N/T/V resulted in reduced or highly reduced inhibition (HRI) by one to three currently available NAIs. D197N reduced inhibition by all NAIs in BR/08 but only by oseltamivir and peramivir in PH/13; R150K caused HRI by all NAIs in PH/13. Although PH/13 generally retained or enhanced NA activity in the presence of the substitutions, enzymatic activity in BR/08 was detrimentally affected. Similarly, substrate affinity and catalysis were relatively stable in PH/13, but not in the BR/08 variants. E105K, R150K, and D197N attenuated replication efficiency of BR/08 in vitro and in mice; only E105K had this effect in PH/13. Notably, the I221 L/N/T/V substitutions did not severely impair replication, particularly in PH/13. Overall, our data show differential effects of NA substitutions in representative Victoria- and Yamagata-lineage viruses, suggesting distinct evolution of these viruses caused variable fitness and NAI susceptibility profiles when similar key NA substitutions arise. Because the viruses harboring the I221 NA substitutions displayed undiminished fitness and are commonly reported, this position is likely to be the most clinically relevant marker for NAI resistance among contemporary influenza B viruses.

Analysis of the vaccine-induced influenza B virus hemagglutinin-specific antibody dependent cellular cytotoxicity response

Influenza A virus (IAV) and influenza B virus (IBV) cause substantial morbidity and mortality during seasonal epidemics. On basis of variation in the surface glycoprotein hemagglutinin, two antigenically distinct lineages of IBV are distinguished: B/Victoria/2/87-like (B/Vic) and B/Yamagata/16/88-like (B/Yam). To prevent IAV and IBV infections, both trivalent (containing IBV of one lineage) and quadrivalent (containing IBV of both lineages) influenza vaccines are used. In addition to virus-neutralizing antibodies, inactivated influenza vaccines induce antibodies that mediate antibody-dependent cellular cytotoxicity (ADCC). Here, we determine whether vaccination with trivalent or quadrivalent inactivated influenza vaccine induces ADCC mediating antibodies directed to IBV of the two different lineages, and whether these antibodies cross-react with IBV of the opposing lineage. A robust ADCC assay based on the use of recombinant hemagglutinin and a continuous natural killer cell line that expresses FcγRIII (CD16) was used to detect the presence of ADCC mediating antibodies. Paired pre- and post-vaccination serum samples from 26 and 15 study subjects that received a trivalent or quadrivalent inactivated influenza vaccine, respectively, were assessed for the presence of ADCC mediating antibodies specific for HA derived from viruses of the B/Vic or B/Yam-lineage. Furthermore, the relative contribution of HA1- and HA2-subunit-specific antibodies to the ADCC response was determined. We found that seasonal inactivated influenza vaccines induce HA-head- and HA-stalk-specific antibodies that mediate ADCC. As expected, the quadrivalent vaccine induced antibodies to HA from both IBV lineages. Notably, a trivalent vaccine containing HA from the B/Vic lineage induced antibodies that cross-react with the B/Yam lineage.

Debate on the compositions of influenza B in northern hemisphere seasonal influenza vaccines

Background

Annual influenza vaccination is the most effective way to prevent influenza. Influenza vaccines have traditionally included the hemagglutinins (HA) and neuraminidases (NA) from the two A viruses (H1N1 and H3N2) and either B Yamagata or B Victoria. Mismatches between circulating isolates of influenza B and the vaccines are very common. Taking 2017/2018 winter in northern hemisphere as an example, this study was designed to find out the reasons for mismatch between the trivalent influenza vaccine (TIV) and most of the epidemic isolates at that time, and to discuss if there are some optimized programs for seasonal influenza vaccines.

Methods

HA and NA sequences of the seasonal isolates circulating from December 1, 2017 to February 28, 2018, and in the previously other 7 winters in northern hemisphere from Global Initiative on Sharing All Influenza Data (GISAID) and the influenza database of National Center for Biotechnology Information (NCBI). Phylogenetic trees and genetic distances were constructed or calculated by using MAFFT and MEGA 6.0 software.

Results

Influenza B composition in the TIV recommendation mismatched most of circulating viruses in 2017/2018 winter; the vaccine strain was from the B/Victoria lineage, while most of epidemic isolates were from the B/Yamagata lineage. The epidemic lineage of influenza B reached its peak a little late in the previous winter might be responsible for this mismatch. During 2010-2018, the mean genetic distances between epidemic isolates of influenza A (H1N1 and H3N2) and the vaccines were no higher than 0.02375 ± 0.00341 in both HA and NA. However, concerning influenza B virus, when forecasting done well, the mean genetic distances between epidemic isolates and the vaccines were no higher than 0.02368 ± 0.00272; otherwise, the distances could reach 0.13695 ± 0.00238.

Conclusion

When applying quadrivalent influenza vaccines (QIVs) for vaccination, the recommendations of compositions for influenza B could be altered and assessed once in 3 or 4 years; when economic burden was considered intensively and TIVs were utilized, the recommended compositions for influenza B could be announced in April or May, rather than in February or March as now.

A Guide for the Use of the Ferret Model for Influenza Virus Infection

As influenza viruses continue to jump species barriers to cause human infection, assessments of disease severity and viral replication kinetics in vivo provide crucial information for public health professionals. The ferret model is a valuable resource for evaluating influenza virus pathogenicity; thus, understanding the most effective techniques for sample collection and usage, as well as the full spectrum of attainable data after experimental inoculation in this species, is paramount. This is especially true for scheduled necropsy of virus-infected ferrets, a standard component in evaluation of influenza virus pathogenicity, as necropsy findings can provide important information regarding disease severity and pathogenicity that is not otherwise available from the live animal. In this review, we describe the range of influenza viruses assessed in ferrets, the measures of experimental disease severity in this model, and optimal sample collection during necropsy of virus-infected ferrets. Collectively, this information is critical for assessing systemic involvement after influenza virus infection in mammals.

Focusing on the Influenza Virus Polymerase Complex: Recent Progress in Drug Discovery and Assay Development

Influenza viruses are severe human pathogens that pose persistent threat to public health. Each year more people die of influenza virus infection than that of breast cancer. Due to the limited efficacy associated with current influenza vaccines, as well as emerging drug resistance from small molecule antiviral drugs, there is a clear need to develop new antivirals with novel mechanisms of action. The influenza virus polymerase complex has become a promising target for the development of the next-generation of antivirals for several reasons. Firstly, the influenza virus polymerase, which forms a heterotrimeric complex that consists of PA, PB1, and PB2 subunits, is highly conserved. Secondly, both individual polymerase subunit (PA, PB1, and PB2) and inter-subunit interactions (PA-PB1, PB1- PB2) represent promising drug targets. Lastly, growing insight into the structure and function of the polymerase complex has spearheaded the structure-guided design of new polymerase inhibitors. In this review, we highlight recent progress in drug discovery and assay development targeting the influenza virus polymerase complex and discuss their therapeutic potentials.

Characteristics of hospitalized adult patients with laboratory documented Influenza A, B and Respiratory Syncytial Virus - A single center retrospective observational study

Introduction

The epidemiology, clinical features and outcomes of hospitalized adult patients with Influenza A (FluA), Influenza B (FluB) and Respiratory Syncytial Virus (RSV) have not been thoroughly compared. The aim of this study was to describe the differences between these viruses during 3 winter seasons.

Methods

A retrospective observational study was conducted consisting of all the polymerase chain reaction (PCR)-based diagnoses of FluA, FluB and RSV among adults during 2015–2018, in one regional hospital. Epidemiology, clinical symptoms and outcome-related data were comparatively analyzed.

Results

Between November 2015 and April 2018, 759 patients were diagnosed with FluA, FluB or RSV. Study cohort included 539 adult patients (306 FluA, 148 FluB and 85 RSV). FluB was predominant during the winter of 2017–18. RSV caused 15.7% of hospitalizations with diagnosed viral infection and in comparison to influenza, had distinct epidemiological, clinical features and outcomes, including older age (74.2 vs 66.2, p = 0.001) and higher rates of co-morbidities; complications including bacterial pneumonia (31 vs 18%, p = 0.02), mechanical ventilation (20 vs 7%, p = 0.001), and viral-related death (13 vs 6.6%, p = 0.04). FluA and FluB had similar epidemiology, clinical symptoms and outcomes, but vaccinated patients were less prone to be hospitalized with FluB as compared with FluA (3 vs 14%, p = 0.001). Paroxysmal atrial fibrillation and falls were common (8.7 and 8.5% respectively).

Conclusions

FluA and FluB had similar epidemiological, clinical features and contributed equally to hospitalization burden and complications. RSV had a major impact on hospitalizations, occurring among the more elderly and sick populations and causing significantly worse outcomes, when compared to influenza patients. Vaccination appeared as a protective factor against hospitalizations with FluB as compared with FluA.