A NEW TYPE OF VIRUS FROM EPIDEMIC INFLUENZA

HA Antigenic variation and phylogenetic analysis of influenza B virus in Shiraz, Iran

BACKGROUND

Influenza is highly contagious respiratory illness triggered by the influenza virus, bearing substantial implications for global health. Influenza B viruses, specifically the Victoria and Yamagata lineages, have contributed to the disease burden, and the mismatch between circulating strains and vaccine strains has led to increased cases and economic costs. Understanding the global epidemiology, seasonal variations, and genetic characteristics of influenza B is crucial for effective prevention and control strategies.

METHODS

The study investigated influenza B viruses in Shiraz during the Oct 2017 to Jan 2018. Throat swabs were collected from 235 individuals under 15 with influenza-like symptoms including fever and cough. Samples were stored at -80°C and transported to the lab for further analysis. Viral RNA was extracted and analyzed using Real-time PCR. The hemagglutinin (HA) gene of positive samples was sequenced, and phylogenetic trees were constructed. Amino acids indicative of adaptive mutations were identified using global sequence data.

RESULTS

23 of 235 samples (9.7%) were positive for influenza B virus. The most common clinical manifestations were rhinorrhea and myalgia, with 20 individuals (87% of the 23 infected people) each showing these symptoms. The phylogenetic analysis of the HA gene showed that the Victoria isolates were close to the B/Brisbane/60/2008 strain (12.5% of the positive samples) and belonged to clade-1A, while the Yamagata isolates were close to the B/Phuket/3037/2013 strain (87.5% of the positive samples) and belonged to clade-3.

CONCLUSION

The study highlights the need for importance vaccine coverage in the Shiraz region to address limited genetic diversity and strain mismatch. Continuous surveillance of mutations in the HA gene resulting in amino acid substitutions and their impact on vaccine efficacy is crucial. This study showed that the circulation of influenza B in Shiraz matched with the recommended Yamagata vaccine strain. These findings contribute to the understanding of influenza B dynamics and emphasize the importance of region-specific prevention and control strategies.

Development of Cross-Reactive Live Attenuated Influenza Vaccine Candidates against Both Lineages of Influenza B Virus

BACKGROUND

Influenza viruses continue to cause a significant social and economic burden globally. Vaccination is recognized as the most effective measure to control influenza. Live attenuated influenza vaccines (LAIVs) are an effective means of preventing influenza, especially among children. A reverse genetics (RG) system is required to rapidly update the antigenic composition of vaccines, as well as to design LAIVs with a broader spectrum of protection. Such a system has been developed for the Russian LAIVs only for type A strains, but not for influenza B viruses (IBV).

METHODS

All genes of the B/USSR/60/69 master donor virus (B60) were cloned into RG plasmids, and the engineered B60, as well as a panel of IBV LAIV reassortants were rescued from plasmid DNAs encoding all viral genes. The engineered viruses were evaluated in vitro and in a mouse model.

RESULTS

The B60 RG system was successfully developed, which made it possible to rescue LAIV reassortants with the desired antigenic composition, including hybrid strains with hemagglutinin and neuraminidase genes belonging to the viruses from different IBV lineages. The LAIV candidate carrying the HA of the B/Victoria-lineage virus and NA from the B/Yamagata-lineage virus demonstrated optimal characteristics in terms of safety, immunogenicity and cross-protection, prompting its further assessment as a broadly protective component of trivalent LAIV.

CONCLUSIONS

The new RG system for B60 MDV allowed the rapid generation of type B LAIV reassortants with desired genome compositions. The generation of hybrid LAIV reassortants with HA and NA genes belonging to the opposite IBV lineages is a promising approach for the development of IBV vaccines with broad cross-protection.

In silico design of a broad-spectrum multiepitope vaccine against influenza virus

Influenza remains a global health concern due to its potential to cause pandemics as a result of rapidly mutating influenza virus strains. Existing vaccines often struggle to keep up with these rapidly mutating flu viruses. Therefore, the development of a broad-spectrum peptide vaccine that can stimulate an optimal antibody response has emerged as an innovative approach to addressing the influenza threat. In this study, an immunoinformatic approach was employed to rapidly predict immunodominant epitopes from different antigens, aiming to develop an effective multiepitope influenza vaccine (MEV). The immunodominant B-cell linear epitopes of seasonal influenza strains hemagglutinin (HA) and neuraminidase (NA) were predicted using an antibody-peptide microarray, involving a human cohort including vaccinees and infected patients. On the other hand, bioinformatics tools were used to predict immunodominant cytotoxic T-cell (CTL) and helper T-cell (HTL) epitopes. Subsequently, these epitopes were evaluated by various immunoinformatic tools. Epitopes with high antigenicity, high immunogenicity, non-allergenicity, non-toxicity, as well as exemplary conservation were then connected in series with appropriate linkers and adjuvants to construct a broad-spectrum MEV. Moreover, the structural analysis revealed that the MEV candidates exhibited good stability, and the docking results demonstrated their strong affinity to Toll-like receptors 4 (TLR4). In addition, molecular dynamics simulation confirmed the stable interaction between TLR4 and MEVs. Three injections with MEVs showed a high level of B-cell and T-cell immune responses according to the immunological simulations in silico. Furthermore, in-silico cloning was performed, and the results indicated that the MEVs could be produced in considerable quantities in Escherichia coli (E. coli). Based on these findings, it is reasonable to create a broad-spectrum MEV against different subtypes of influenza A and B viruses in silico.

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.

A computationally optimized broadly reactive hemagglutinin vaccine elicits neutralizing antibodies against influenza B viruses from both lineages

Influenza B viruses (IBV) can cause severe disease and death much like influenza A viruses (IAV), with a disproportionate number of infections in children. Despite moving to a quadrivalent vaccine to include strains from both the B/Victoria and B/Yamagata lineages, vaccine effectiveness rates continue to be variable and low in many past seasons. To develop more effective influenza B virus vaccines, three novel IBV hemagglutinin (HA) vaccines were designed using a computationally optimized broadly reactive antigen (COBRA) methodology. These IBV HA proteins were expressed on the surface of a virus-like particle (VLP) and used to vaccinate ferrets that were pre-immune to historical B/Victoria or B/Yamagata lineage viruses. Ferrets vaccinated with B-COBRA HA vaccines had neutralizing antibodies with high titer HAI titer against all influenza B viruses regardless of pre-immunization history. Conversely, VLPs expressing wild-type IBV HA antigens preferentially boosted titers against viruses from the same lineage and there was little-to-no seroprotective antibodies detected in ferrets with mismatched IBV pre-immune infections. Overall, a single IBV HA developed using the COBRA methodology elicited protective broadly-reactive antibodies against current and future drifted IBVs from both lineages.

Epidemiological characteristics of seasonal influenza under implementation of zero-COVID-19 strategy in China

OBJECTIVE

Respiratory viral diseases have posed a persistent threat to public health due to their high transmissibility. Influenza virus and SARS-Cov-2 are both respiratory viruses that have caused global pandemics. A zero-COVID-19 strategy is a public health policy imposed to stop community transmission of COVID-19 as soon as it is detected. In this study, we aim to examine the epidemiological characteristics of seasonal influenza in the past five years before and after the emergence of COVID-19 in China and observe the possible impact of the strategy on influenza.

METHODS

Data from two data sources were retrospectively analyzed. A comparison on influenza incidence rate between Hubei and Zhejiang provinces was conducted based on data from the Chinese Center for Disease Control and Prevention (CDC). Then a descriptive and comparative analysis on seasonal influenza based on data from Zhongnan Hospital of Wuhan University and Hangzhou Ninth People`s Hospital before and after the outbreak of SARS-CoV-2 was conducted.

RESULTS

From 2010-2017, both provinces experienced relatively low influenza activity until the 1st week of 2018, when they reached peak incidence rates of 78.16/100000PY, 34.05/100000PY respectively. Since then, influenza showed an obvious seasonality in Hubei and Zhejiang until the onset of COVID-19. During 2020 and 2021, there was a dramatic decline in influenza activity compared to 2018 and 2019. However, influenza activity seemed to rebound at the beginning of 2022 and surged in summer, with positive rates of 20.52% and 31.53% in Zhongnan Hospital of Wuhan University and Hangzhou Ninth People`s Hospital respectively as of the time writing this article.

CONCLUSIONS

Our results reinforce the hypothesis that zero-COVID-19 strategy may impact the epidemiological pattern of influenza. Under the complex pandemic situation, implementation of NPIs could be a beneficial strategy containing not only COVID-19 but also influenza.

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.

Increasing serum antibodies against type B influenza virus in 2017-2018 winter in Beijing, China

Influenza B virus circulates yearly with lower activity than that of influenza A virus in China. During winter 2017 to 2018, a sharp surge of influenza activity dominated by type B/Yamagata lineage virus caused unprecedented medical burden in Beijing. This research aimed to understand the underlying mechanism for this circulation and prepare for epidemics in the future. Sera samples collected from the patients in 2016–2017 and 2017–2018 flu seasons were tested for profiling hemagglutinin inhibition (HI) antibodies against both prevailing Victoria and Yamagata lineages of type B influenza viruses. It showed that the seroprevalence against both lineages of the virus in 2017–2018 winter was higher than that in 2016–2017, while no difference of the seroprevalence was observed between the two viruses. Meanwhile, significant elevated geometric mean titer (GMT) against both lineages of influenza B viruses was found in the specimens collected during 2017–2018 flu season than that from 2016 to 2017, suggesting the viruses might undergo antigenic changes. These results also suggested that lower GMT against both type B variants in 2016–2017 might serve as an immunological niche for the dominating of B/Yamagata virus in China during 2017–2018 winter season. Our findings have implication that there was a significantly elevation of HI antibodies to influenza viruses B in 2017–2018 than in 2016–2017. On the other hand, the low level of HI antibodies to both B/Y and B/V in 2016–2017 could contribute to the severe B/Y epidemic in 2017–2018 to some extent.

An overview of advancement in aptasensors for influenza detection

INTRODUCTION

The platforms for early identification of infectious diseases such as influenza has seen a surge in recent years as delayed diagnosis of such infections can lead to dreadful effects causing large numbers of deaths. The time taken in detection of an infectious disease may vary from a few days to a few weeks depending upon the choice of the techniques. So, there is an urgent need for advanced methodologies for early diagnosis of the influenza.

AREAS COVERED

The emergence of "Aptasensor" synergistically with biosensors for diagnosis has opened a new era for sensitive, selective and early detection approaches. This review described various conventional as well as advanced methods based on artificial immunogenic nucleotide sequences complementing a part of the virus, i.e., aptamers based aptasensors for influenza diagnosis and the challenges faced in their commercialization.

EXPERT OPINION

Although numerous traditional methods are available for influenza detection but mostly associated with low sensitivity, specificity, high cost, trained personnel, and animals required for virus culture/ antibody raising as the major drawbacks. Aptamers can be manufactured invitro as 'chemical antibodies' at commercial level, no animal required. Following these advantages, aptamers can pave the way for an efficient diagnostic technique as compared to other existing conventional methods..

The Spanish Flu

The Spanish flu occurred at the end of the First World War, in disastrous epidemiological conditions on populations exhausted by four years of war. At that time, there were no vaccines, no antibiotics, no oxygen and no resuscitation. It was even thought that the infectious agent was a bacterium. Humanity was poorly equipped to fight against a pandemic that caused 50-100 million deaths. The first palpable signs of the outbreak were the rapidly spreading multiple epidemics among young recruits in the American military training camps in March 1918. The flu then spread to the civilian populations and circled the globe twice, sparing no country, even the most remote islands, in tropical as well as polar climates, evolving in successive waves up until April 1919. The first was mild (lethality 0.21%), the second was lethal (lethality 2-4%), and during the third wave, lethality declined (1%), after which the flu became seasonal, with low lethality (0.1%). Between 20 and 40 years of age, patients often died within a few days of pneumonia, with respiratory distress leading to cyanosis, frequently associated with bacterial superinfection. The influenza virus, Myxovirus influenzae, was first discovered in 1931 by Richard Shope in pigs, and then in 1933 by Wilson Smith, Patrick Laidlaw and Christopher Andrews in humans during a seasonal influenza epidemic in London. In 1943, it was first observed under the electron microscope. Hemagglutinin and neuraminidase, the two main virulence factors, were discovered in the 1940s by George Hirst and Alfred Gottschalk. An RNA virus composed of 13,500 nucleotides in eight segments, it was initially sequenced in the 1980s, when Jeffrey Taubenberger determined the complete nucleotide sequence of the 1918 virus from lung tissue samples from patients who died of influenza. The 1918 H1N1 virus was found to have originated in birds. In 2005, it was successfully resuscitated in cell culture. It is 40,000 times more virulent in primates than the seasonal H1N1 virus. The lethality of the second wave could have been due to mutations in the hemagglutinin H1 gene, which would have resulted in a stronger affinity for α,2-6 galactose sialic acids, the virus' receptors on human epithelial cells. That said, the origin of the Spanish flu virus remains controversial. It probably emerged and circulated in the population before March 1918 in America, although European origin has also been evoked. The high mortality in the 20-40 age group remains an enigma. Some experts point to reduced immune response in patients previously exposed to related viral hemagglutinins during the 1889 pandemic. In any event, even though it concerns a markedly different virus, the history of the Spanish flu sheds light on the difficulties of management during today's pandemic.

A Comprehensive Roadmap Towards the Generation of an Influenza B Reporter Assay Using a Single DNA Polymerase-Based Cloning of the Reporter RNA Construct

The mini-genome reporter assay is a key tool for conducting RNA virus research. However, procedural complications and the lack of adequate literature pose a major challenge in developing these assay systems. Here, we present a novel, yet generic and simple, cloning strategy for the construction of an influenza B virus reporter RNA template and describe an extensive standardization of the reporter RNP/polymerase activity assay for monitoring viral RNA synthesis in an infection-free setting. Using this assay system, we showed for the first time the effect of viral protein NS1 and host protein kinase C delta (PKCD) on influenza B virus RNA synthesis. In addition, the assay system showed promising results in evaluating the efficacy of antiviral drugs targeting viral RNA synthesis and virus propagation. Together, this work offers a detailed protocol for the standardization of the influenza virus minigenome assay and an excellent tool for screening of host factors and antivirals in a fast, user-friendly, and high-throughput manner.

Using amino acid features to identify the pathogenicity of influenza B virus

BACKGROUND

Influenza B virus can cause epidemics with high pathogenicity, so it poses a serious threat to public health. A feature representation algorithm is proposed in this paper to identify the pathogenicity phenotype of influenza B virus.

METHODS

The dataset included all 11 influenza virus proteins encoded in eight genome segments of 1724 strains. Two types of features were hierarchically used to build the prediction model. Amino acid features were directly delivered from 67 feature descriptors and input into the random forest classifier to output informative features about the class label and probabilistic prediction. The sequential forward search strategy was used to optimize the informative features. The final features for each strain had low dimensions and included knowledge from different perspectives, which were used to build the machine learning model for pathogenicity identification.

RESULTS

The 40 signature positions were achieved by entropy screening. Mutations at position 135 of the hemagglutinin protein had the highest entropy value (1.06). After the informative features were directly generated from the 67 random forest models, the dimensions for class and probabilistic features were optimized as 4 and 3, respectively. The optimal class features had a maximum accuracy of 94.2% and a maximum Matthews correlation coefficient of 88.4%, while the optimal probabilistic features had a maximum accuracy of 94.1% and a maximum Matthews correlation coefficient of 88.2%. The optimized features outperformed the original informative features and amino acid features from individual descriptors. The sequential forward search strategy had better performance than the classical ensemble method.

CONCLUSIONS

The optimized informative features had the best performance and were used to build a predictive model so as to identify the phenotype of influenza B virus with high pathogenicity and provide early risk warning for disease control.

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.

Serological Responses to Influenza Vaccination during Pregnancy

Pregnant women, newborns, and infants under six months old are at the highest risk of developing severe and even fatal influenza. This risk is compounded by the inability to vaccinate infants under six months, highlighting the importance of vertically transferred immunity. This review identifies novel insights that have emerged from recent studies using animal models of pregnancy and vaccination. We also discuss the knowledge obtained using existing clinical trials that have evaluated influenza-specific serological responses in pregnant women and how these responses may impact early life immunity. We delineate the mechanisms involved in transferring specific maternal antibodies and discuss the consequences for early life immunity. Most importantly, we highlight the need for continued research using pregnant animal models and the inclusion of pregnant women, a commonly neglected population, when evaluating novel vaccine platforms to better serve and treat communicable diseases.

Cell-Adapted Mutations and Antigenic Diversity of Influenza B Viruses in Missouri, 2019-2020 Season

Influenza B viruses (IBVs) are causing an increasing burden of morbidity and mortality, yet the prevalence of culture-adapted mutations in human seasonal IBVs are unclear. We collected 368 clinical samples from patients with influenza-like illness in Missouri during the 2019–2020 influenza season and recovered 146 influenza isolates including 38 IBV isolates. Of MDCK-CCL34, MDCK-Siat1, and humanized MDCK (hCK), hCK showed the highest virus recovery efficiency. All Missourian IBVs belonged to the Victoria V1A.3 lineage, all of which contained a three-amino acid deletion on the HA protein and were antigenically distant from the Victoria lineage IBV vaccine strain used during that season. By comparing genomic sequences of these IBVs in 31 paired samples, eight cell-adapted nonsynonymous mutations were identified, with the majority in the RNA polymerase. Analyses of IBV clinical sample–isolate pairs from public databases further showed that cell- and egg-adapted mutations occurred more widely in viral proteins, including the receptor and antibody binding sites on HA. Our study suggests that hCK is an effective platform for IBV isolation and that culture-adapted mutations may occur during IBV isolation. As culture-adapted mutations may affect subsequent virus studies and vaccine development, the knowledge from this study may help optimize strategies for influenza surveillance, vaccine strain selection, and vaccine development.

FluB-RAM and FluB-RANS: Genome Rearrangement as Safe and Efficacious Live Attenuated Influenza B Virus Vaccines

Influenza B virus (IBV) is considered a major respiratory pathogen responsible for seasonal respiratory disease in humans, particularly severe in children and the elderly. Seasonal influenza vaccination is considered the most efficient strategy to prevent and control IBV infections. Live attenuated influenza virus vaccines (LAIVs) are thought to induce both humoral and cellular immune responses by mimicking a natural infection, but their effectiveness has recently come into question. Thus, the opportunity exists to find alternative approaches to improve overall influenza vaccine effectiveness. Two alternative IBV backbones were developed with rearranged genomes, rearranged M (FluB-RAM) and a rearranged NS (FluB-RANS). Both rearranged viruses showed temperature sensitivity in vitro compared with the WT type B/Bris strain, were genetically stable over multiple passages in embryonated chicken eggs and were attenuated in vivo in mice. In a prime-boost regime in naïve mice, both rearranged viruses induced antibodies against HA with hemagglutination inhibition titers considered of protective value. In addition, antibodies against NA and NP were readily detected with potential protective value. Upon lethal IBV challenge, mice previously vaccinated with either FluB-RAM or FluB-RANS were completely protected against clinical disease and mortality. In conclusion, genome re-arrangement renders efficacious LAIV candidates to protect mice against IBV.

Animal Models Utilized for the Development of Influenza Virus Vaccines

Animal models have been an important tool for the development of influenza virus vaccines since the 1940s. Over the past 80 years, influenza virus vaccines have evolved into more complex formulations, including trivalent and quadrivalent inactivated vaccines, live-attenuated vaccines, and subunit vaccines. However, annual effectiveness data shows that current vaccines have varying levels of protection that range between 40–60% and must be reformulated every few years to combat antigenic drift. To address these issues, novel influenza virus vaccines are currently in development. These vaccines rely heavily on animal models to determine efficacy and immunogenicity. In this review, we describe seasonal and novel influenza virus vaccines and highlight important animal models used to develop them.

Respiratory RNA Viruses: How to Be Prepared for an Encounter with New Pandemic Virus Strains

The characteristics of the biology of influenza viruses and coronavirus that determine the implementation of the infectious process are presented. With provision for pathogenesis of infection possible effects of serine proteinase inhibitors, heparin, and inhibitors of heparan sulfate receptors in the prevention of cell contamination by viruses are examined. It has been determined that chelators of metals of variable valency and antioxidants should be used for the reduction of replicative activity of viruses and anti-inflammatory therapy. The possibility of a pH-dependent impairment of glycosylation of cellular and viral proteins was traced for chloroquine and its derivatives. The use of low-toxicity drugs as part of adjunct therapy increases the effectiveness of synthetic antiviral drugs and interferons and ensures the safety of baseline therapy.

The past, present and future of RNA respiratory viruses: influenza and coronaviruses

Influenza virus and coronaviruses continue to cause pandemics across the globe. We now have a greater understanding of their functions. Unfortunately, the number of drugs in our armory to defend us against them is inadequate. This may require us to think about what mechanisms to address. Here, we review the biological properties of these viruses, their genetic evolution and antiviral therapies that can be used or have been attempted. We will describe several classes of drugs such as serine protease inhibitors, heparin, heparan sulfate receptor inhibitors, chelating agents, immunomodulators and many others. We also briefly describe some of the drug repurposing efforts that have taken place in an effort to rapidly identify molecules to treat patients with COVID-19. While we put a heavy emphasis on the past and present efforts, we also provide some thoughts about what we need to do to prepare for respiratory viral threats in the future.

Reverse genetics for influenza B viruses and recent advances in vaccine development

Influenza B virus is a respiratory pathogen that affects more severely the pediatric and elderly populations. There are two lineages of influenza B virus that seem to have differential predilection for age groups. Both lineages can co-circulate during the influenza season however one is usually more prominent than the other depending on the season. There are no defined indicators to predict which lineage will dominate in any given season. In recent years, the addition of viruses from both lineages to the seasonal influenza vaccine formulation has improved vaccine protection, although quadrivalent vaccines are not available worldwide. Reverse genetics has facilitated advancements in the field of vaccine development against influenza B virus. Different strategies have been explored showing promising results that could potentially lead to the development broadly protective influenza B virus vaccines.

A Systematic Review Analyzing the Prevalence and Circulation of Influenza Viruses in Swine Population Worldwide

The global anxiety and a significant threat to public health due to the current COVID-19 pandemic reiterate the need for active surveillance for the zoonotic virus diseases of pandemic potential. Influenza virus due to its wide host range and zoonotic potential poses such a significant threat to public health. Swine serve as a “mixing vessel” for influenza virus reassortment and evolution which as a result may facilitate the emergence of new strains or subtypes of zoonotic potential. In this context, the currently available scientific data hold a high significance to unravel influenza virus epidemiology and evolution. With this objective, the current systematic review summarizes the original research articles and case reports of all the four types of influenza viruses reported in swine populations worldwide. A total of 281 articles were found eligible through screening of PubMed and Google Scholar databases and hence were included in this systematic review. The highest number of research articles (n = 107) were reported from Asia, followed by Americas (n = 97), Europe (n = 55), Africa (n = 18), and Australia (n = 4). The H1N1, H1N2, H3N2, and A(H1N1)pdm09 viruses were the most common influenza A virus subtypes reported in swine in most countries across the globe, however, few strains of influenza B, C, and D viruses were also reported in certain countries. Multiple reports of the avian influenza virus strains documented in the last two decades in swine in China, the United States, Canada, South Korea, Nigeria, and Egypt provided the evidence of interspecies transmission of influenza viruses from birds to swine. Inter-species transmission of equine influenza virus H3N8 from horse to swine in China expanded the genetic diversity of swine influenza viruses. Additionally, numerous reports of the double and triple-reassortant strains which emerged due to reassortments among avian, human, and swine strains within swine further increased the genetic diversity of swine influenza viruses. These findings are alarming hence active surveillance should be in place to prevent future influenza pandemics.

Epidemiology and Genetic Variability of Circulating Influenza B Viruses in Uruguay, 2012-2019

Influenza B viruses (IBV) are an important cause of morbidity and mortality during interpandemic periods in the human population. Two phylogenetically distinct IBV lineages, B/Yamagata and B/Victoria, co-circulate worldwide and they present challenges for vaccine strain selection. Until the present study, there was little information regarding the pattern of the circulating strains of IBV in Uruguay. A subset of positive influenza B samples from influenza-like illness (ILI) outpatients and severe acute respiratory illness (SARI) inpatients detected in sentinel hospitals in Uruguay during 2012–2019 were selected. The sequencing of the hemagglutinin (HA) and neuraminidase (NA) genes showed substitutions at the amino acid level. Phylogenetic analysis reveals the co-circulation of both lineages in almost all seasonal epidemics in Uruguay, and allows recognizing a lineage-level vaccine mismatch in approximately one-third of the seasons studied. The epidemiological results show that the proportion of IBV found in ILI was significantly higher than the observed in SARI cases across different groups of age (9.7% ILI, 3.2% SARI) and patients between 5–14 years constituted the majority (33%) of all influenza B infection (p < 0.05). Interestingly, we found that individuals >25 years were particularly vulnerable to Yamagata lineage infections.

Evolutionary dynamics of influenza B strains detected from paediatric acute respiratory infections in central Vietnam

Influenza virus B belongs to the family Orthomyxoviridae with segmented negative-sense RNA genomes. Since 1970s, influenza B has diverged intoVictoria and Yamagata, which differs in antigenic and evolutionary characteristics. Yet, molecular-epidemiological information of influenza B from developing nations is limited. In central Vietnam, influenza A subtype-specific circulation pattern and clinical characteristics were previously described. However, molecular evolutionary characteristics of influenza B has not been discussed to date. We utilized the influenza B positives obtained from paediatric ARI surveillance during 2007-2013. Influenza B HA and NA genes were amplified, sequenced, and phylogenetic/molecular evolutionary analysis was performed using Maximum Likelihood and Bayesian MCMC. Phylodynamics analysis was performed with Bayesian Skyline Plot (BSP). Furthermore, we performed selection pressure analysis and estimated N-glycosylation sites. In the current study, overall positive rate for influenza B was 3.0%, and Victoria lineage immediately became predominant in post-A/H1N1pdm09 period. The noticeable shift in Victoria lineage WHO Group occurred. With respect to the evolutionary rate (substitutions/site/year), Victoria lineage HA gene was evolving faster than Yamagata lineage (2.43 × 10^-3 vs 2.00 × 10^-3). Furthermore, the evolutionary rate of Victoria Group 5 was greater than Group 1. BSP presented the rapid growth in Effective Population Size (EPS) of Victoria lineage occurred soon after the 1st A/H1N1pdm09 case was detected whereas the EPS of Yamagata lineage was stable for both genes. N-glycosylation pattern between lineages and among WHO Groups were slightly different, and HA gene had a total of 6 amino acid substitutions under positive section pressure (4 for Victoria and 2 for Yamagata). The current results highlight the importance of Victoria lineage in post-A/H1N1pdm09 period. Difference in evolutionary characteristics and phylodynamics may indicate lineage and WHO Group-specific evolutionary dynamics. It is necessary to further continue the molecular-epidemiological surveillance in local setting to gain a better understanding of local evolutionary characteristics of influenza B strains.

Epidemiological features and trends of influenza incidence in mainland China: A population-based surveillance study from 2005 to 2015

OBJECTIVES

To investigate epidemiological features and trends of influenza incidence with 1,173,640 cases in mainland China from 2005 to 2015.

METHODS

Incidence and mortality data for influenza from 2005 to 2015 were provided by the data-center of China public health science and covered a population of about 1.3 billion people from 31 provinces and regions in mainland China. Joinpoint regression and exploratory spatial data analyses were used to examine the incidence trends from 2005 to 2015.

RESULTS

The first upsurge in influenza cases occurred in 2009, and the highest incidence of influenza occurred in 2014 (15.9045 cases/100,000 people). The average incidence per year from 2009 to 2015 was threefold higher than that from 2005 to 2008 (10.5308 vs 3.4589 cases/100,000 people; incidence rate ratio=3.0446). The joinpoint regression results showed that there was an increasing influenza incidence trend from 2005 to 2015 (annual change in percentage=13.6%, 95%CI 2.2-26.3, p=0.0236). The seasonal pattern analysis showed that influenza typically occurred in winter and spring during each monitoring year, peaking from November to March the next year.

CONCLUSIONS

This study will help governments to make valuable decisions in allocating scarce resources and providing strategies to limit the spread of influenza.

Tropism of influenza B viruses in human respiratory tract explants and airway organoids

Despite causing regular seasonal epidemics with substantial morbidity, mortality and socioeconomic burden, there is still a lack of research into influenza B viruses (IBVs). In this study, we provide for the first time a systematic investigation on the tropism, replication kinetics and pathogenesis of IBVs in the human respiratory tract.Physiologically relevant ex vivo explant cultures of human bronchus and lung, human airway organoids, and in vitro cultures of differentiated primary human bronchial epithelial cells and type-I-like alveolar epithelial cells were used to study the cellular and tissue tropism, replication competence and induced innate immune response of 16 IBV strains isolated from 1940 to 2012 in comparison with human seasonal influenza A viruses (IAVs), H1N1 and H3N2. IBVs from the diverged Yamagata- and Victoria-like lineages and the earlier undiverged period were included.The majority of IBVs replicated productively in human bronchus and lung with similar competence to seasonal IAVs. IBVs infected a variety of cell types, including ciliated cells, club cells, goblet cells and basal cells, in human airway organoids. Like seasonal IAVs, IBVs are low inducers of pro-inflammatory cytokines and chemokines. Most results suggested a higher preference for the conducting airway than the lower lung and strain-specific rather than lineage-specific pathogenicity of IBVs.Our results highlighted the non-negligible virulence of IBVs which require more attention and further investigation to alleviate the disease burden, especially when treatment options are limited.

The Development and Use of Reporter Influenza B Viruses

Influenza B viruses (IBVs) are major contributors to total human influenza disease, responsible for ~1/3 of all infections. These viruses, however, are relatively less studied than the related influenza A viruses (IAVs). While it has historically been assumed that the viral biology and mechanisms of pathogenesis for all influenza viruses were highly similar, studies have shown that IBVs possess unique characteristics. Relative to IAV, IBV encodes distinct viral proteins, displays a different mutational rate, has unique patterns of tropism, and elicits different immune responses. More work is therefore required to define the mechanisms of IBV pathogenesis. One valuable approach to characterize mechanisms of microbial disease is the use of genetically modified pathogens that harbor exogenous reporter genes. Over the last few years, IBV reporter viruses have been developed and used to provide new insights into the host response to infection, viral spread, and the testing of antiviral therapeutics. In this review, we will highlight the history and study of IBVs with particular emphasis on the use of genetically modified viruses and discuss some remaining gaps in knowledge that can be addressed using reporter expressing IBVs.

Broadly Cross-Reactive, Nonneutralizing Antibodies against Influenza B Virus Hemagglutinin Demonstrate Effector Function-Dependent Protection against Lethal Viral Challenge in Mice

Protection from influenza virus infection is canonically associated with antibodies that neutralize the virus by blocking the interaction between the viral hemagglutinin and host cell receptors. However, protection can also be conferred by other mechanisms, including antibody-mediated effector functions. Here, we report the characterization of 22 broadly cross-reactive, nonneutralizing antibodies specific for influenza B virus hemagglutinin. The majority of these antibodies recognized influenza B viruses isolated over the period of 73 years and bind the conserved stalk domain of the hemagglutinin. A proportion of the characterized antibodies protected mice from both morbidity and mortality after challenge with a lethal dose of influenza B virus. Activity in an antibody-dependent cell-mediated cytotoxicity reporter assay correlated strongly with protection, suggesting that Fc-dependent effector function determines protective efficacy. The information regarding mechanism of action and epitope location stemming from our characterization of these antibodies will inform the design of urgently needed vaccines that could induce broad protection against influenza B viruses.IMPORTANCE While broadly protective antibodies against the influenza A virus hemagglutinin have been well studied, very limited information is available for antibodies that broadly recognize influenza B viruses. Similarly, the development of a universal or broadly protective influenza B virus vaccine lags behind the development of such a vaccine for influenza A virus. More information about epitope location and mechanism of action of broadly protective influenza B virus antibodies is required to inform vaccine development. In addition, protective antibodies could be a useful tool to treat or prevent influenza B virus infection in pediatric cohorts or in a therapeutic setting in immunocompromised individuals in conjugation with existing treatment avenues.

Molecular evolution of influenza B virus during 2011-2017 in Chaoyang, Beijing, suggesting the free influenza vaccine policy

Two influenza B virus lineages, B/Victoria and B/Yamagata, are co-circulating in human population. While the two lineages are serologically distinct and TIV only contain one lineage. It is important to investigate the epidemiological and evolutionary dynamics of two influenza B virus lineages in Beijing after the free influenza vaccine policy from 2007. Here, we collected the nasopharyngeal swabs of 12657 outpatients of influenza-like illness and subtyped by real-time RT-PCR during 2011–2017. The HA and NA genes of influenza B were fully sequenced. The prevalence is the highest in the 6–17 years old group among people infected with influenza B. Yamagata-lineage virus evolved to two inter-clade from 2011–2014 to 2014–2017. The amino acids substitutions of HA1 region were R279K in strains of 2011–2014 and L173Q, M252V in strains of 2014–2017. Substitutions L58P, I146V were observed in HA1 region of Victoria-lineage virus in 2011–2012 and I117V, N129D were showed in 2015–2017. Phylogenetic analysis of NA showed Yamagata-Victoria inter-lineage reassortant occurred in 2013–2014. Influenza B mainly infect the school-aged children in Beijing and the free influenza vaccine inoculation does not seem to block school-age children from infection with influenza B. The antigen characteristics of circulating influenza B were different to the recommended vaccine strains. We concluded that the Victoria-lineage vaccine strain should been changed and the free influenza vaccine should be revalued.

Emerging Influenza D Virus Threat: What We Know so Far!

Influenza viruses, since time immemorial, have been the major respiratory pathogen known to infect a wide variety of animals, birds and reptiles with established lineages. They belong to the family Orthomyxoviridae and cause acute respiratory illness often during local outbreaks or seasonal epidemics and occasionally during pandemics. Recent studies have identified a new genus within the Orthomyxoviridae family. This newly identified pathogen, D/swine/Oklahoma/1334/2011 (D/OK), first identified in pigs with influenza-like illness was classified as the influenza D virus (IDV) which is distantly related to the previously characterized human influenza C virus. Several other back-to-back studies soon suggested cattle as the natural reservoir and possible involvement of IDV in the bovine respiratory disease complex was established. Not much is known about its likelihood to cause disease in humans, but it definitely poses a potential threat as an emerging pathogen in cattle-workers. Here, we review the evolution, epidemiology, virology and pathobiology of influenza D virus and the possibility of transmission among various hosts and potential to cause human disease.

Influenza B viruses in pigs, Taiwan

Background

Influenza B viruses (IBVs) have never been isolated from natural‐infected pigs in clinical cases, although the susceptibility of domestic pigs to experimental IBV infections had been confirmed as well as IBV‐specific antibodies were detected from pigs under natural and experimental conditions.

Objectives

We aimed to assess and investigate the activities for infection and circulation of IBVs in pigs.

Methods

Annual active surveys for influenza have been implemented on swine populations in Taiwan since July 1998. Nasal swabs, trachea, lungs, and blood from pigs were tested using virological and serological assays for influenza. Gene sequences of influenza viral isolates were determined and characterized. Preliminary sero‐epidemiological data for influenza virus were investigated.

Results

Three strains of IBV were isolated and identified from natural‐infected pigs in 2014. Genetic characterization revealed the highest identities (>99%) of molecular sequence with the contemporary IBVs belonged to the B/Brisbane/60/2008 genetic clade of Victoria lineage in the phylogenetic trees for all 8 genes. IBV‐specific antibodies were detected in 31 (0.2%; 95%CI: 0.1%‐0.2%) of 15 983 swine serum samples from 29 (2.8%; 95%CI: 1.9%‐3.9%) of 1039 farm visits under annual active surveys from 2007 through 2017. Seropositive cases have been found sparsely in 1‐5 of test prefectures every year except 2015 and 2017 as well as scattered loosely over 26 townships/districts of 11 prefectures in Taiwan cumulatively in 11 years.

Conclusions

Influenza B viruse infections from humans to pigs remained sporadic and accidental currently in Taiwan but might have paved potential avenues for newly emerging zoonotic influenza in the future.

The Spanish Flu, Epidemics, and the Turn to Biomedical Responses

A century ago, nonpharmaceutical interventions such as school closings, restrictions on large gatherings, and isolation and quarantine were the centerpiece of the response to the Spanish Flu. Yet, even though its cause was unknown and the science of vaccine development was in its infancy, considerable enthusiasm also existed for using vaccines to prevent its spread. This desire far exceeded the scientific knowledge and technological capabilities of the time. Beginning in the early 1930s, however, advances in virology and influenza vaccine development reshaped the relative priority given to biomedical approaches in epidemic response over traditional public health activities. Today, the large-scale implementation of nonpharmaceutical interventions akin to the response to the Spanish Flu would face enormous legal, ethical, and political challenges, but the enthusiasm for vaccines and other biomedical interventions that was emerging in 1918 has flourished. The Spanish Flu functioned as an inflection point in the history of epidemic responses, a critical moment in the long transition from approaches dominated by traditional public health activities to those in which biomedical interventions are viewed as the most potent and promising tools in the epidemic response arsenal.

The continual threat of influenza virus infections at the human-animal interface: What is new from a one health perspective?

This year, in 2018, we mark 100 years since the 1918 influenza pandemic. In the last 100 years, we have expanded our knowledge of public health and increased our ability to detect and prevent influenza; however, we still face challenges resulting from these continually evolving viruses. Today, it is clear that influenza viruses have multiple animal reservoirs (domestic and wild), making infection prevention in humans especially difficult to achieve. With this report, we summarize new knowledge regarding influenza A, B, C and D viruses and their control. We also introduce how a multi-disciplinary One Health approach is necessary to mitigate these threats.

Variation in Influenza B Virus Epidemiology by Lineage, China

We used national sentinel surveillance data in China for 2005-2016 to examine the lineage-specific epidemiology of influenza B. Influenza B viruses circulated every year with relatively lower activity than influenza A. B/Yamagata was more frequently detected in adults than in children.

Universal influenza virus vaccines and therapeutics: where do we stand with influenza B virus?

The development of a broadly protective or universal influenza virus vaccine is currently a public health priority worldwide. The vast majority of these efforts is exclusively focused on influenza A viruses. While influenza A viruses cause the majority of all influenza cases worldwide, influenza B viruses should not be ignored. Approximately 25% of all influenza cases are caused by influenza B viruses which circulate as two distinct B/Victoria/2/87-like and B/Yamagata/16/88-like lineages. In contrast to popular belief, influenza B cases frequently cause significant morbidity and mortality, especially in children. Similar to influenza A viruses, influenza B viruses drift antigenically and the influenza B components of current vaccines have to be reformulated almost on an annual basis. A broadly protective vaccine against influenza B viruses is therefore urgently needed. Here we review both broadly protective anti-influenza B antibodies as well as the sparse attempts to create a universal influenza B virus vaccine.

Neurologic Complications of Influenza B Virus Infection in Adults, Romania

Infection with this virus should be considered as an etiologic factor for encephalitis.

We characterized influenza B virus–related neurologic manifestations in an unusually high number of hospitalized adults at a tertiary care facility in Romania during the 2014–15 influenza epidemic season. Of 32 patients with a confirmed laboratory diagnosis of influenza B virus infection, neurologic complications developed in 7 adults (median age 31 years). These complications were clinically diagnosed as confirmed encephalitis (4 patients), possible encephalitis (2 patients), and cerebellar ataxia (1 patient). Two of the patients died. Virus sequencing identified influenza virus B (Yam)-lineage clade 3, which is representative of the B/Phuket/3073/2013 strain, in 4 patients. None of the patients had been vaccinated against influenza. These results suggest that influenza B virus can cause a severe clinical course and should be considered as an etiologic factor for encephalitis.

Influenza Virus: Dealing with a Drifting and Shifting Pathogen

Numerous modern technological and scientific advances have changed the vaccine industry. However, nearly 70 years of influenza vaccine usage have passed without substantial changes in the underlying principles of the vaccine. The challenge of vaccinating against influenza lies in the constantly changing nature of the virus itself. Influenza viruses undergo antigenic evolution through antigenic drift and shift in their surface glycoproteins. This has forced frequent updates of vaccine antigens to ensure that the somewhat narrowly focused vaccine-induced immune responses defend against circulating strains. Few vaccine production systems have been developed that can entertain such constant changes. Although influenza virus infection induces long-lived immunologic memory to the same or similar strains, most people do not encounter the same strain repeatedly in their lifespan, suggesting that enhancement of natural immunity is required to improve influenza vaccines. It is clear that transformative change of influenza vaccines requires a rethink of how we immunize. In this study, we review the problems associated with the changing nature of the virus, and highlight some of the approaches being employed to improve influenza vaccines.

Primary Human Influenza B Virus Infection Induces Cross-Lineage Hemagglutinin Stalk-Specific Antibodies Mediating Antibody-Dependent Cellular Cytoxicity

Influenza A virus (IAV) and influenza B virus (IBV) cause substantial morbidity and mortality during annual epidemics. Two distinct lineages of IBV are distinguished, based on variation in hemagglutinin (HA): B/Victoria/2/87-like (B/Vic) and B/Yamagata/16/88-like (B/Yam). Here, we show that, in humans, primary IBV infection with either lineage induces HA-specific antibody-dependent cellular cytotoxicity (ADCC)-mediating antibodies. IBV infection induced antibodies specific to the HA head and stalk, but only HA stalk-specific antibodies mediated ADCC efficiently and displayed cross-reactivity with IBV of both lineages. This corresponds to recent findings that 2 points of contact between the effector and target cell (ie, HA and sialic acid, respectively, and the fragment crystallizable [Fc] domain and Fcγ receptor IIIα, respectively) are required for efficient ADCC activity and that antibodies specific for the receptor-binding site located in the head domain of HA therefore fail to mediate ADCC. Potentially, ADCC-mediating antibodies directed to the HA stalk of IBV contribute to cross-protective immunity to IBV of both lineages.

Chimeric Hemagglutinin Constructs Induce Broad Protection against Influenza B Virus Challenge in the Mouse Model

Seasonal influenza virus epidemics represent a significant public health burden. Approximately 25% of all influenza virus infections are caused by type B viruses, and these infections can be severe, especially in children. Current influenza virus vaccines are an effective prophylaxis against infection but are impacted by rapid antigenic drift, which can lead to mismatches between vaccine strains and circulating strains. Here, we describe a broadly protective vaccine candidate based on chimeric hemagglutinins, consisting of globular head domains from exotic influenza A viruses and stalk domains from influenza B viruses. Sequential vaccination with these constructs in mice leads to the induction of broadly reactive antibodies that bind to the conserved stalk domain of influenza B virus hemagglutinin. Vaccinated mice are protected from lethal challenge with diverse influenza B viruses. Results from serum transfer experiments and antibody-dependent cell-mediated cytotoxicity (ADCC) assays indicate that this protection is antibody mediated and based on Fc effector functions. The present data suggest that chimeric hemagglutinin-based vaccination is a viable strategy to broadly protect against influenza B virus infection.IMPORTANCE While current influenza virus vaccines are effective, they are affected by mismatches between vaccine strains and circulating strains. Furthermore, the antiviral drug oseltamivir is less effective for treating influenza B virus infections than for treating influenza A virus infections. A vaccine that induces broad and long-lasting protection against influenza B viruses is therefore urgently needed.

Epidemiology of influenza B/Yamagata and B/Victoria lineages in South Africa, 2005-2014

Background

Studies describing the epidemiology of influenza B lineages in South Africa are lacking.

Methods

We conducted a prospective study to describe the circulation of influenza B/Victoria and B/Yamagata lineages among patients of all ages enrolled in South Africa through three respiratory illness surveillance systems between 2005 and 2014: (i) the Viral Watch (VW) program enrolled outpatients with influenza-like illness (ILI) from private healthcare facilities during 2005–2014; (ii) the influenza-like illnesses program enrolled outpatients in public healthcare clinics (ILI/PHC) during 2012–2014; and (iii) the severe acute respiratory illnesses (SARI) program enrolled inpatients from public hospitals during 2009–2014. Influenza B viruses were detected by virus isolation during 2005 to 2009 and by real-time reverse transcription polymerase chain reaction from 2009–2014. Clinical and epidemiological characteristics of patients hospitalized with SARI and infected with different influenza B lineages were also compared using unconditional logistic regression.

Results

Influenza viruses were detected in 22% (8,706/39,804) of specimens from patients with ILI or SARI during 2005–2014, of which 24% (2,087) were positive for influenza B. Influenza B viruses predominated in all three surveillance systems in 2010. B/Victoria predominated prior to 2011 (except 2008) whereas B/Yamagata predominated thereafter (except 2012). B lineages co-circulated in all seasons, except in 2013 and 2014 for SARI and ILI/PHC surveillance. Among influenza B-positive SARI cases, the detection of influenza B/Yamagata compared to influenza B/Victoria was significantly higher in individuals aged 45–64 years (adjusted odds ratio [aOR]: 4.2; 95% confidence interval [CI]: 1.1–16.5) and ≥65 years (aOR: 12.2; 95% CI: 2.3–64.4) compared to children aged 0–4 years, but was significantly lower in HIV-infected patients (aOR: 0.4; 95% CI: 0.2–0.9).

Conclusion

B lineages co-circulated in most seasons except in 2013 and 2014. Hospitalized SARI cases display differential susceptibility for the two influenza B lineages, with B/Victoria being more prevalent among children and HIV-infected persons.

Single nucleoprotein residue determines influenza A virus sensitivity to an intertypic suppression mechanism

Several mechanisms underlying intertypic interference between co-infecting influenza types A and B viruses (IAV and IBV) have been proposed. We have recently described one in which IBV's nucleoprotein (BNP) sequestered IAV's nucleoprotein (ANP) and suppressed IAV polymerase and growth. However, its anti-IAV capacity and limitations have not been fully explored. Here, we showed that BNP's inhibitory effect was more potent toward a wide array of avian IAVs, whereas human IAVs revealed moderate resistance. BNP sensitivity was largely determined by ANP's residue 343 at the NP oligomerization interface. An avian IAV polymerase carrying an NP-V343L mutation switched from being highly BNP-sensitive to moderately BNP-resistant, and vice versa for a human IAV polymerase carrying a reverse mutation. To highlight its capacity, we demonstrated that the polymerases of highly-pathogenic H5N1 and the pandemic 2009 (H1N1) strains are strongly inhibited by BNP. Our work provides insights into lineage-specific sensitivity to BNP-mediated intertypic interference.

Knowns and unknowns of influenza B viruses

Influenza B viruses (IBVs) circulate annually along with influenza A (IAV) strains during seasonal epidemics. IBV can dominate influenza seasons and cause severe disease, particularly in children and adolescents. Research has revealed interesting aspects of IBV and highlighted the importance of these viruses in clinical settings. Yet, many important questions remain unanswered. In this review, the clinical relevance of IBV is emphasized, unique features in epidemiology, host range and virology are highlighted and gaps in knowledge pinpointed. Multiple aspects of IBV epidemiology, evolution, virology and immunology are discussed. Future research into IBV is needed to understand how we can prevent severe disease in high-risk groups, especially children and elderly.

Influenza B viruses: not to be discounted

In contrast to influenza A viruses, which have been investigated extensively, influenza B viruses have attracted relatively little attention. However, influenza B viruses are an important cause of morbidity and mortality in the human population and full understanding of their biological and epidemiological properties is imperative to better control this important pathogen. However, some of its characteristics are still elusive and warrant investigation. Here, we review evolution, epidemiology, pathogenesis and immunity and identify gaps in our knowledge of influenza B viruses. The divergence of two antigenically distinct influenza B viruses is highlighted. The co-circulation of viruses of these two lineages necessitated the development of quadrivalent influenza vaccines, which is discussed in addition to possibilities to develop universal vaccination strategies.