The coming era of quadrivalent human influenza vaccines: who will benefit?

Mosaic neuraminidase-based vaccine induces antigen-specific T cell responses against homologous and heterologous influenza viruses

Seasonal influenza is an annually severe crisis for global public health, and an ideal influenza vaccine is expected to provide broad protection against constantly drifted strains. Compared to highly flexible hemagglutinin (HA), increasing data have demonstrated that neuraminidase (NA) might be a potential target against influenza variants. In the present study, a series of genetic algorithm-based mosaic NA were designed, and then cloned into recombinant DNA and replication-defective Vesicular Stomatitis Virus (VSV) vector as a novel influenza vaccine candidate. Our Results showed that DNA prime/VSV boost strategy elicited a robust NA-specific Th1-dominated immune response, but the traditional inactivated influenza vaccine elicited a Th2-dominated immune response. More importantly, the superior NA-specific immunity induced by our strategy could confer both a full protection against lethal homologous influenza challenge and a partial protection against heterologous influenza infection. These findings will provide insights on designing NA-based universal vaccine strategy against influenza variants.

Immunogenicity and safety of inactivated quadrivalent influenza vaccine compared with the trivalent vaccine for influenza infection: an overview of systematic reviews

BACKGROUND

Influenza infection is a highly preventable transmissible viral disease associated with mild upper respiratory symptoms and more severe conditions such as lethal pneumonia. Studies have shown that a broader spectrum influenza vaccine could reduce influenza's burden of disease in low- and middle-income countries. A considerable number of systematic reviews reported that quadrivalent influenza vaccines are considered more effective compared to trivalent vaccines, hence, there is a need for an overview in order to synthesize the current evidence pertaining to the comparison between quadrivalent and trivalent inactivated influenza vaccines.

OBJECTIVE

The aim was to summarize the evidence from systematic reviews that investigated the immunogenicity and safety of the Influenza's inactivated quadrivalent vaccine (QIV) compared to the trivalent vaccine (TIV), in the general population.

METHODS

We searched articles up to December 2022 at: Web of Science, EMBASE, MEDLINE, Cochrane Library, and SCOPUS. The search strategy was conducted following the PICO model. We included systematic reviews comparing the primary outcomes of immunogenicity (seroprotection rate and seroconversion rate) and adverse events using risk ratios. The AMSTAR 2 and ROBIS were used for quality assessments, and GRADE was used for evidence certainty assessments.

FINDINGS

We included five systematic reviews, totalling 47,740 participants. The Quadrivalent Inactivated Influenza Vaccine (QIV) exhibited enhanced immunogenicity in the context of B-lineage mismatch when compared to the Trivalent Inactivated Influenza Vaccine (TIV). While the safety profile of QIV was found to be comparable to that of TIV, the QIV showed a higher incidence of solicited local pain among children and adolescents, as well as an increased frequency of local adverse events within the adult population.

CONCLUSION

Our findings suggest that the QIV provides a superior immunogenicity response compared to the TIV in all age groups evaluated, especially when a lineage mismatch occurred. The safety of QIV was considered similar to the TIV, with no serious or systemic solicited or unsolicited adverse events; tough pain at the injection site was greater for QIV. We recommend caution owing to the high risk of bias in the selection process and no protocol registration.

Genetic Diversity and Evolutionary Kinetics of Influenza A Virus H3N2 Subtypes Circulating in Riyadh, Saudi Arabia

Presence of a large foreign workforce and the annual gathering of people for pilgrimage from around the globe have significantly contributed to the emergence and diversity of respiratory viruses in Saudi Arabia. Here, we report the sequence and phylogenetic analysis of the H3N2 subtype of influenza A virus (IAV) in clinical samples collected from Riyadh, Saudi Arabia. Based on RT-PCR, IAV was found in 88 (28.3%) of the 311 samples screened. Of the 88-IAV positive samples, 43 (48.8%) were H1N1 subtype while the remaining 45 (51.2%) were found to be of the H3N2 subtype. Complete sequencing of HA and NA genes of H3N2 revealed, twelve and nine amino acid (AA) substitutions respectively, and importantly, these variations are absent in the current vaccine strains. Based on the phylogenetic analysis, the majority of H3N2 strains were grouped in the same clades as the vaccine strains. Importantly, the N-glycosylation sites at AA 135(NSS) were found to be unique to 6 strains in the investigated HA1 protein and were absent in the current vaccine strains. These data may have significant clinical implications in designing novel and population-based vaccines for IAV and underscore the need for regular monitoring of efficacy of vaccines due to emerging variants.

Public health and budget impacts of switching from a trivalent to a quadrivalent inactivated influenza vaccine in Paraguay

This study aimed to investigate the public health and economic benefit of using a quadrivalent influenza vaccine (QIV) instead of a trivalent influenza vaccine (TIV) in past seasons in Paraguay. The budget impact of switching from TIV to QIV in the Immunization Program was also evaluated. The adapted model includes two modules. The first compared retrospectively Health and Economic outcomes resulting from the use of QIV instead of TIV. The second forecast the spending and savings that would be associated with the switch from TIV to QIV. Our findings estimate that the switch from TIV to QIV during the seasons 2012 to 2017 could have prevented around 2,600 influenza cases, 67 hospitalizations and 10 deaths. An alternative scenario using standardized estimates of the burden of influenza showed that 234 influenza-related hospitalizations and 29 deaths could have been prevented. The estimated annual budget impact of a full switch from TIV to QIV was around USD1,6 million both from the payer and societal perspectives. Those results are mainly driven by vaccine prices and coverage rate. In sum, this manuscript describes how the use of QIV instead of TIV could have prevented influenza cases and subsequent complications that led to hospitalizations and deaths. This could have generated savings for the health system and society, offsetting part of the additional investment needed to switch from TIV to QIV.

Antigenic comparison of the neuraminidases from recent influenza A vaccine viruses and 2019-2020 circulating strains

Although viral-based influenza vaccines contain neuraminidase (NA or N) antigens from the recommended seasonal strains, NA is not extensively evaluated like hemagglutinin (H) during the strain selection process. Here, we compared the antigenicity of NAs from recently recommended H1N1 (2010–2021 seasons) and H3N2 (2015–2021 seasons) vaccine strains and viruses that circulated between September 2019 and December 2020. The antigenicity was evaluated by measuring NA ferret antisera titers that provide 50% inhibition of NA activity in an enzyme-linked lectin assay. Our results show that NAs from circulating H1N1 viruses and vaccine strains for the 2017–2021 seasons are all antigenically similar and distinct from the NA in the H1N1 strain recommended for the 2010–2017 seasons. Changes in N1 antigenicity were attributed to the accumulation of substitutions over time, especially the loss of an N-linked glycosylation site (Asn386) in current N1s. The NAs from circulating H3N2 viruses and the 2020–2021 vaccine strains showed similar antigenicity that varied across the N2s in the 2016–2020 vaccine strains and was distinct from the N2 in the 2015–2016 vaccine strain. These data suggest that the recent N1 antigenicity has remained similar since the loss of the head domain N-linked glycosylation site, whereas N2 antigenicity has changed more incrementally each season.

Lineage-matched versus mismatched influenza B vaccine effectiveness following seasons of marginal influenza B circulation

BACKGROUND

Several countries have recently transitioned from the trivalent inactivated influenza vaccine (TIV) to the quadrivalent inactivated influenza vaccine (QIV) in order to outweigh influenza B vaccine-mismatch. However, few studies thus far evaluated its benefits versus the TIV in a systematic manner. Our objective was to compare the QIV VE with lineage-mismatched TIV VE.

METHODS

We estimated the 2015-2016, 2017-2018, 2019-2020 end-of season influenza B VE against laboratory-confirmed influenza-like illness (ILI) among community patients, using the test-negative design. VE was estimated for pre-determined age groups and for moving age intervals of 15 years.

RESULTS

Since 2011-2012 season, alternate seasons in Israel were dominated by influenza B circulation. Compared with the lineage-mismatched TIV used during the 2015-2016 and 2017-2018 seasons, the 2019-2020 QIV showed the highest all-ages VE, with VE estimates of 56.9 (95% CI 30.1 to 73.4), 16.5 (95% CI -22.5 to 43.1) and -25.8 (95% CI -85.3 to 14.6) for the 2019-2020, 2017-2018 and 2015-2016 seasons, respectively. The 2019-2020 VE point estimated were the highest for the 0.5-4, 5-17 and 18-44 years age groups and for more 15-year age intervals as compared to the other seasons.

CONCLUSIONS

Our results support the rapid transition from the TIV to the QIV.

Cost-effectiveness analysis of switching from a trivalent to a quadrivalent inactivated influenza vaccine in the Peruvian immunisation programme

BACKGROUND

Seasonal influenza is an acute respiratory infection mostly caused by type A and B influenza viruses. The severe form of the infection can be life-threatening and lead to a significant burden. Vaccination is the most efficient way of preventing influenza infections and limit this burden.

OBJECTIVES

To assess the cost-effectiveness of switching from a trivalent influenza vaccine (TIV) to a quadrivalent influenza vaccine (QIV) in the vaccination programme in Peru, and to evaluate the health and economic impact of reaching the vaccination coverage rate targeted by the Ministry of Health.

METHODS

A decision-analytic static cost-effectiveness model, was adapted to the Peruvian setting under both payer and societal perspectives.

RESULTS

A switch from TIV to QIV would prevent 29,126 additional cases (including 12,815 consultations), 54 hospitalisations, and 23 deaths related to influenza, mostly in the population <2 years-old and >60 years-old. This would lead to a saving of US $505,206 under the payer perspective, that would partially offset the investment necessary to introduce QIV into the immunisation programme. The resulting incremental cost-effectiveness ratio (ICER) is $16,649 per QALYs gained. The main drivers of the model results were vaccine efficacy against influenza B viruses, degree of match, vaccines prices and proportion of cases attributable to influenza B. The robustness of the results seems satisfactory as QIV has the probability of being a cost-effective strategy of 83.8% (considering a threshold of three GDP per capita). Reaching the coverage targeted by the Ministry of Health would result in health benefits and disease management savings, and lower ICERs.

CONCLUSION

Introducing QIV instead of TIV in the Peruvian immunisation programme is expected to be a cost-effective strategy, especially in younger children and the elderly. The benefit of QIV would be even more important if the coverage targeted by the Ministry of Health would be reached in the most vulnerable groups.

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.

Challenges of Making Effective Influenza Vaccines

Seasonal influenza vaccines prevent influenza-related illnesses, hospitalizations, and deaths. However, these vaccines are not as effective as other viral vaccines, and there is clearly room for improvement. Here, we review the history of seasonal influenza vaccines, describe challenges associated with producing influenza vaccine antigens, and discuss the inherent difficulties of updating influenza vaccine strains each influenza season. We argue that seasonal influenza vaccines can be dramatically improved by modernizing antigen production processes and developing models that are better at predicting viral evolution. Resources should be specifically dedicated to improving seasonal influenza vaccines while developing entirely new vaccine platforms.

From trivalent to quadrivalent influenza vaccines: Public health and economic burden for different immunization strategies in Spain

PURPOSE

Quadrivalent influenza vaccine (QIV) includes the same strains as trivalent influenza vaccine (TIV) plus an additional B strain of the other B lineage. The aim of the study was to analyse the public health and economic impact of replacing TIV with QIV in different scenarios in Spain.

METHODS

A dynamic transmission model was developed to estimate the number of influenza B cases prevented under TIV and QIV strategies (<65 years (high risk) and ≥65 years). This model considers cross-protective immunity induced by different lineages of influenza B. The output of the transmission model was used as input for a decision tree model that estimated the economic impact of switching TIV to QIV. The models were populated with Spanish data whenever possible. Deterministic univariate and probabilistic multivariate sensitivity analyses were performed.

RESULTS

Replacing TIV with QIV in all eligible patients with current vaccine coverage in Spain may have prevented 138,707 influenza B cases per season and, therefore avoided 10,748 outpatient visits, 3,179 hospitalizations and 192 deaths. The replacement could save €532,768 in outpatient visit costs, €13 million in hospitalization costs, and €3 million in costs of influenza-related deaths per year. An additional €5 million costs associated with productivity loss could be saved per year, from the societal perspective. The budget impact from societal perspective would be €6.5 million, and the incremental cost-effectiveness ratio (ICER) €1,527 per quality-adjusted life year (QALY). Sensitivity analyses showed robust results. In additional scenarios, QIV also showed an impact at public health level reducing influenza B related cases, outpatient visits, hospitalizations and deaths.

CONCLUSIONS

Our results show public health and economic benefits for influenza prevention with QIV. It would be an efficient intervention for the Spanish National Health Service with major health benefits especially in the population ≥65-year.

IgA Responses Following Recurrent Influenza Virus Vaccination

Influenza is a highly contagious viral respiratory disease that affects millions of people worldwide each year. Annual vaccination is recommended by the World Health Organization to reduce influenza severity and limit transmission through elicitation of antibodies targeting mainly the hemagglutinin glycoprotein of the influenza virus. Antibodies elicited by current seasonal influenza vaccines are predominantly strain-specific. However, continuous antigenic drift by circulating influenza viruses facilitates escape from pre-existing antibodies requiring frequent reformulation of the seasonal influenza vaccine. Traditionally, immunological responses to influenza vaccination have been largely focused on IgG antibodies, with almost complete disregard of other isotypes. In this report, young adults (18–34 years old) and elderly (65–85 years old) subjects were administered the split inactivated influenza vaccine for 3 consecutive seasons and their serological IgA and IgG responses were profiled. Moreover, correlation analysis showed a positive relationship between vaccine-induced IgA antibody titers and traditional immunological endpoints, exposing vaccine-induced IgA antibodies as an important novel immune correlate during influenza vaccination.

Impact of early neuraminidase inhibitor treatment on clinical outcomes in patients with influenza B-related pneumonia: a multicenter cohort study

The aim of this study is to evaluate the impact of early (within 2 days after disease onset) neuraminidase inhibitor (NAI) administration on clinical outcomes in patients with laboratory-confirmed influenza B-related pneumonia (FluB-p). This was a multicenter study conducted from 1 January 2013 to 1 May 2019. Data of immunocompetent adult and adolescent FluB-p patients hospitalized at five different teaching hospitals in China were retrospectively collected, including demographic and clinical features as well as clinical and treatment outcomes. Univariate and multivariate logistic regression analyses were performed to assess the effects of early NAI administration on clinical outcomes in FluB-p patients. In total, 386 hospitalized patients with community-onset FluB-p were included in this study, of whom 39.6% (153/386) were treated with NAI early. After adjusting for the weighted propensity scores of treatment, systemic corticosteroid, and antibiotic uses, the results of multivariate logistic regression model indicated that early NAI treatment was associated with the decreased risks of invasive ventilation [odd ratio (OR) 0.325, 95% confidence interval (CI) 0.123-0.858; p = 0.023), admittance to intensive care unit (OR 0.425, 95% CI 0.204-0.882; p = 0.022), and 30-day mortality (OR 0.416, 95% CI 0.184-0.944, p = 0.036)] in FluB-p patients. In addition, the multivariate logistic regression analysis revealed that early NAI treatment (OR 0.306, 95% CI 0.063-0.618; p = 0.010) was an independent predictor for 30-day mortality in patients with FluB-p. Early NAI treatment was associated with better clinical outcomes in FluB-p patients, which supports the recommendations of its use in severe influenza illness.

Preexisting subtype immunodominance shapes memory B cell recall response to influenza vaccination

Influenza is a highly contagious viral pathogen with more than 200,000 cases reported in the United States during the 2017-2018 season. Annual vaccination is recommended by the World Health Organization, with the goal to reduce influenza severity and transmission. Currently available vaccines are about 60% effective, and vaccine effectiveness varies from season to season, as well as between different influenza subtypes within a single season. Immunological imprinting from early-life influenza infection can prominently shape the immune response to subsequent infections. Here, the impact of preexisting B cell memory in the response to quadrivalent influenza vaccine was assessed using blood samples collected from healthy subjects (18-85 years old) prior to and 21-28 days following influenza vaccination. Influenza vaccination increased both HA-specific antibodies and memory B cell frequency. Despite no apparent differences in antigenicity between vaccine components, most individuals were biased toward one of the vaccine strains. Specifically, responses to H3N2 were reduced in magnitude relative to the other vaccine components. Overall, this study unveils a potentially new mechanism underlying differential vaccine effectiveness against distinct influenza subtypes.

Co-circulation of the two influenza B lineages during 13 consecutive influenza surveillance seasons in Italy, 2004-2017

BACKGROUND

Since 1985, two antigenically distinct lineages of influenza B viruses (Victoria-like and Yamagata-like) have circulated globally. Trivalent seasonal influenza vaccines contain two circulating influenza A strains but a single B strain and thus provide limited immunity against circulating B strains of the lineage not included in the vaccine. In this study, we describe the characteristics of influenza B viruses that caused respiratory illness in the population in Italy over 13 consecutive seasons of virological surveillance, and the match between the predominant influenza B lineage and the vaccine B lineage, in each season.

METHODS

From 2004 to 2017, 26,886 laboratory-confirmed influenza cases were registered in Italy, of which 18.7% were type B. Among them, the lineage of 2465 strains (49%) was retrieved or characterized in this study by a real-time RT-PCR assay and/or sequencing of the hemagglutinin (HA) gene.

RESULTS

Co-circulation of both B lineages was observed each season, although in different proportions every year. Overall, viruses of B/Victoria and B/Yamagata lineages caused 53.3 and 46.7% of influenza B infections, respectively. A higher proportion of infections with both lineages was detected in children, and there was a declining frequency of B/Victoria detections with age. A mismatch between the vaccine and the predominant influenza B lineage occurred in eight out of thirteen influenza seasons under study. Considering the seasons when B accounted for > 20% of all laboratory-confirmed influenza cases, a mismatch was observed in four out of six seasons. Phylogenetic analysis of the HA1 domain confirmed the co-circulation of both lineages and revealed a mixed circulation of distinct evolutionary viral variants, with different levels of match to the vaccine strains.

CONCLUSIONS

This study contributes to the understanding of the circulation of influenza B viruses in Italy. We found a continuous co-circulation of both B lineages in the period 2004-2017, and determined that children were particularly vulnerable to Victoria-lineage influenza B virus infections. An influenza B lineage mismatch with the trivalent vaccine occurred in about two-thirds of cases.

The Epidemiology and Burden of Influenza B/Victoria and B/Yamagata Lineages in Kenya, 2012-2016

BACKGROUND

The impact of influenza B virus circulation in Sub-Saharan Africa is not well described.

METHODS

We analyzed data from acute respiratory illness (ARI) in Kenya. We assessed clinical features and age-specific hospitalization and outpatient visit rates by person-years for influenza B/Victoria and B/Yamagata and the extent to which circulating influenza B lineages in Kenya matched the vaccine strain component of the corresponding season (based on Northern Hemisphere [October-March] and Southern Hemisphere [April-September] vaccine availability).

RESULTS

From 2012 to 2016, influenza B represented 31% of all influenza-associated ARIs detected (annual range, 13-61%). Rates of influenza B hospitalization and outpatient visits were higher for <5 vs ≥5 years. Among <5 years, B/Victoria was associated with pneumonia hospitalization (64% vs 44%; P = .010) and in-hospital mortality (6% vs 0%; P = .042) compared with B/Yamagata, although the mean annual hospitalization rate for B/Victoria was comparable to that estimated for B/Yamagata. The 2 lineages co-circulated, and there were mismatches with available trivalent influenza vaccines in 2/9 seasons assessed.

CONCLUSIONS

Influenza B causes substantial burden in Kenya, particularly among children aged <5 years, in whom B/Victoria may be associated with increased severity. Our findings suggest a benefit from including both lineages when considering influenza vaccination in Kenya.

Cell-Based Quadrivalent Inactivated Influenza Virus Vaccine (Flucelvax® Tetra/Flucelvax Quadrivalent®): A Review in the Prevention of Influenza

Manufacturing influenza virus vaccines using a mammalian cell line rather than embryonated chicken eggs may carry certain advantages. A quadrivalent inactivated influenza virus vaccine produced using the Madin Darby canine kidney cell line has been approved in the EU (Flucelvax^® Tetra) and USA (Flucelvax Quadrivalent^®; QIVc hereafter) for the prevention of influenza in adults and children. The clinical development of QIVc has built upon that of a cell-based trivalent influenza virus vaccine (TIVc) manufactured using the same processes; the additional influenza B strain contained in QIVc reduces the risk of the strain in the vaccine not matching that in circulation. Pivotal phase III clinical trials in adult and paediatric participants have demonstrated the immunogenicity of QIVc to be noninferior to that of TIVc formulations against shared strains and superior against the influenza B strain absent from each TIVc formulation. Protective efficacy data for TIVc is considered foundational for QIVc and, in a phase III clinical trial, TIVc was effective in protecting adults against antigenically matched influenza strains. Large real-world studies from the 2017/2018 US influenza season further support the prophylactic effectiveness of QIVc, with possible benefits over egg-based vaccines. QIVc was generally well tolerated in clinical trials. In adult and paediatric QIVc recipients, the most common solicited adverse reactions were injection site pain and headache. Reactogenicity was comparable to that of TIVc; no safety signals unique to QIVc emerged. Through circumventing concerns around egg adaptation, QIVc has the potential to be more effective than currently available egg-based quadrivalent vaccines.

Rationale for vaccination with trivalent or quadrivalent live attenuated influenza vaccines: Protective vaccine efficacy in the ferret model

BACKGROUND AND AIM

The majority of seasonal influenza vaccines are trivalent, containing two A virus strains (H1N1 and H3N2) and one B virus strain. The co-circulation of two distinct lineages of B viruses can lead to mismatch between the influenza B virus strain recommended for the trivalent seasonal vaccine and the circulating B virus. This has led some manufacturers to produce quadrivalent influenza vaccines containing one strain from each B lineage in addition to H1N1 and H3N2 strains. However, it is also important to know whether vaccines containing a single influenza B strain can provide cross-protectivity against viruses of the antigenically distinct lineage. The aim of this study was to assess in naïve ferrets the potential cross-protective activity of trivalent live attenuated influenza vaccine (T-LAIV) against challenge with a heterologous wild-type influenza B virus belonging to the genetically different lineage and to compare this activity with effectiveness of quadrivalent LAIV (Q-LAIV) in the ferret model.

METHODS AND RESULTS

Ferrets were vaccinated with either one dose of trivalent LAIV containing B/Victoria or B/Yamagata lineage virus, or quadrivalent LAIV (containing both B lineages), or placebo. They were then challenged with B/Victoria or B/Yamagata lineage wild-type virus 28 days after vaccination. The ferrets were monitored for clinical signs and morbidity. Nasal swabs and lung tissue samples were analyzed for the presence of challenge virus. Antibody response to vaccination was assessed by routine hemagglutination inhibition assay. All LAIVs tested were found to be safe and effective against wild-type influenza B viruses based on clinical signs, and virological and histological data. The absence of interference between vaccine strains in trivalent and quadrivalent vaccine formulations was confirmed. Trivalent LAIVs were shown to have the potential to be cross-protective against infection with genetically different influenza B/Victoria and B/Yamagata lineages.

CONCLUSIONS

In this ferret model, quadrivalent vaccine provided higher protection to challenge against both B/Victoria and B/Yamagata lineage viruses. However, T-LAIV provided some cross-protection in the case of a mismatch between circulating and vaccine type B strains. Notably, B/Victoria-based T-LAIV was more protective compared to B/Yamagata-based T-LAIV.

Influenza B viruses circulated during last 5 years in Mongolia

Influenza B virus-caused illness has recently been considered as an urgent public health problem due to substantial morbidity, mortality and life-threatening medical complications. In this study, we have reported the main characteristics of influenza B virus in Mongolia, including prevalence, lineages, suitability with vaccine strains and drug susceptibility against the virus. 15768 specimens were tested by qPCR for detecting influenza viruses. From positive specimens for influenza B virus, the clinical isolates were isolated using MDCK cells. Sequencing analysis, hemagglutination inhibition assay and Neuraminidase inhibitor (NAI) drug susceptibility testing were performed for the clinical isolates. Influenza B virus was around in 3.46% of the samples in Mongolia, and B/Victoria clade-1A and B/Yamagata clade-3 lineages were predominant. Importantly, it was confirmed that the lineages corresponded to the vaccine strains. Moreover, drug susceptibility tests revealed that some Mongolian clinical isolates showed reduced susceptibility to antiviral agents. Interestingly, G104R was identified as a novel mutation, which might have a significant role in drug resistance of the virus. These results describe the characteristics of influenza B viruses that have caused respiratory illness in the population of Mongolia between 2013 and 2017.

Rapid detection of new B/Victoria-lineage haemagglutinin variants of influenza B viruses by pyrosequencing

During 2016/2017, several antigenically and genetically distinct variant viruses of the influenza B/Victoria/2/87-lineage (B/Vic) viruses, which have either deletions or mutations in the haemagglutinin (HA) emerged and co-circulated with other influenza B viruses from both the B/Vic and B/Yamagata/16/88-lineages (B/Yam). In this study we developed a pyrosequencing assay that can detect and differentiate multiple influenza B virus variants currently in circulation. The assay targets a region of HA sequence that is unique for each of the B/Yam, B/Vic and B/Vic variant viruses. Our results demonstrated that it is a rapid, robust, high-throughput assay, highly sensitive and specific in differentiating among the B/Yam, B/Vic and B/Vic variant viruses, giving it an advantage over an existing rRT-PCR method. It works well for influenza virus isolates as well as original clinical respiratory specimens, and can therefore be used to provide important information for surveillance by closely monitoring the spread of these B/Vic variants.

[Seasonal flu vaccination for older people: Evaluation of the quadrivalent vaccine. Positioning report]

Influenza is a significant health problem, particularly in those persons susceptible to having associated complications, older people, children less than 2 years, patients with chronic diseases, immunocompromised patients, and pregnant women. But influenza also has a large impact on the health system, with an increase in the healthcare demand and a spectacular increase in outpatient visits, overloading the emergency and hospital services. During epidemic outbreaks, the hospital admission rates of people over 65 years are at a maximum, and the mortality notified for the 2017/2018 influenza season was 960 deaths. The seasonal anti-influenza vaccine is the method with a better cost-effective ratio of primary prevention of influenza, reducing associated respiratory diseases, the number of hospital admissions, and deaths in high risk individuals, as well as work absenteeism in adults. In the last few years, influenza B has received little attention in the scientific literature, although in the periods between epidemics influenza B can be one of the main causes of seasonal epidemics, causing considerable morbidity and mortality and an increase in costs. The quadrivalent vaccine has a second-line immunological protection against influenza B, and according to a critical review of the scientific literature, it provides wider protection without affecting immunogenicity of the other three vaccine strains common to the trivalent and tetravalent vaccine. The quadrivalent vaccine is cost-effective in reducing the number of influenza cases, and is always a worthwhile intervention, with a significant cost saving for the health system and for society, by reducing the hospital admission rates and mortality associated with the complications of influenza. Supplement information: This article is part of a supplement entitled 'Seasonal flu vaccination for older people: Evaluation of the quadrivalent vaccine' which is sponsored by Sanofi-Aventis, S.A.

Influenza surveillance in Western Turkey in the era of quadrivalent vaccines: A 2003-2016 retrospective analysis

Human influenza is predominantly caused by influenza A virus (IAV) - A/H1N1 and/or A/H3N2 - and influenza B virus (IBV) - B/Victoria and/or B/Yamagata, which co-circulate each season. Influenza surveillance provides important information on seasonal disease burden and circulation, and vaccine content for the following season. To study the circulating influenza subtypes/lineages in western Turkey. Community-based sentinel surveillance results during 2003-2016 (weeks 40-20 each season; but week 21, 2009 through week 20, 2010 during the pandemic) were analyzed. Nasal/nasopharyngeal swabs from patients with influenza-like illness were tested for influenza virus and characterized as A/H1N1, A/H3N2, or IBV. A subset of IBV samples was further characterized as B/Victoria or B/Yamagata. Among 14,429 specimens (9,766 collected during interpandemic influenza seasons; 4,663 during the 2009-2010 pandemic), 3,927 (27.2%) were positive. Excluding the pandemic year (2009-2010), 645 (27.4%) samples were characterized as A/H1N1 or A/H1N1/pdm09, 958 (40.7%) as A/H3N2, and 752 (31.9%) as IBV, but the dominant subtype/lineage varied widely each season. During the pandemic year (2009-2010), 98.3% of cases were A/H1N1/pdm09. IBV accounted for 0-60.2% of positive samples each season. The IBV lineages in circulation matched the vaccine IBV lineage >50% in six seasons and <50% in four seasons; with an overall mismatch of 49.7%. IBV cases tended to peak later than IAV cases within seasons. These results have important implications for vaccine composition and optimal vaccination timing. Quadrivalent vaccines containing both IBV lineages can reduce B-lineage mismatch, thus reducing the burden of IBV disease.

Literature review of the epidemiology of influenza B disease in 15 countries in the Asia-Pacific region

Influenza control strategies focus on the use of trivalent influenza vaccines containing two influenza A virus subtypes and one of the two circulating influenza type B lineages (Yamagata or Victoria). Mismatches between the vaccine B lineage and the circulating lineage have been regularly documented in many countries, including those in the Asia‐Pacific region. We conducted a literature review with the aim of understanding the relative circulation of influenza B viruses in Asia‐Pacific countries. PubMed and Western Pacific Region Index Medicus were searched for relevant articles on influenza type B published since 1990 in English language for 15 Asia‐Pacific countries. Gray literature was also accessed. From 4834 articles identified, 121 full‐text articles were analyzed. Influenza was reported as an important cause of morbidity in the Asia‐Pacific region, affecting all age groups. In all 15 countries, influenza B was identified and associated with between 0% and 92% of laboratory‐confirmed influenza cases in any one season/year. Influenza type B appeared to cause more illness in children aged between 1 and 10 years than in other age groups. Epidemiological data for the two circulating influenza type B lineages remain limited in several countries in the Asia‐Pacific, although the co‐circulation of both lineages was seen in countries where strain surveillance data were available. Mismatches between circulating B lineages and vaccine strains were observed in all countries with available data. The data suggest that a shift from trivalent to quadrivalent seasonal influenza vaccines could provide additional benefits by providing broader protection.

The cost-effectiveness of trivalent and quadrivalent influenza vaccination in communities in South Africa, Vietnam and Australia

BACKGROUND

To inform national healthcare authorities whether quadrivalent influenza vaccines (QIVs) provide better value for money than trivalent influenza vaccines (TIVs), we assessed the cost-effectiveness of TIV and QIV in low-and-middle income communities based in South Africa and Vietnam and contrasted these findings with those from a high-income community in Australia.

METHODS

Individual based dynamic simulation models were interfaced with a health economic analysis model to estimate the cost-effectiveness of vaccinating 15% of the population with QIV or TIV in each community over the period 2003-2013. Vaccination was prioritized for HIV-infected individuals, before elderly aged 65+ years and young children. Country or region-specific data on influenza-strain circulation, clinical outcomes and costs were obtained from published sources. The societal perspective was used and outcomes were expressed in International$ (I$) per quality-adjusted life-year (QALY) gained.

RESULTS

When compared with TIV, we found that QIV would provide a greater reduction in influenza-related morbidity in communities in South Africa and Vietnam as compared with Australia. The incremental cost-effectiveness ratio of QIV versus TIV was estimated at I$4183/QALY in South Africa, I$1505/QALY in Vietnam and I$80,966/QALY in Australia.

CONCLUSIONS

The cost-effectiveness of QIV varied between communities due to differences in influenza epidemiology, comorbidities, and unit costs. Whether TIV or QIV is the most cost-effective alternative heavily depends on influenza B burden among subpopulations targeted forvaccination in addition to country-specific willingness-to-pay thresholds and budgetary impact.

Evidence for Viral Interference and Cross-reactive Protective Immunity Between Influenza B Virus Lineages

Background

Two influenza B virus lineages, B/Victoria and B/Yamagata, cocirculate in the human population. While the lineages are serologically distinct, cross-reactive responses to both lineages have been detected. Viral interference describes the situation whereby infection with one virus limits infection and replication of a second virus. We investigated the potential for viral interference between the influenza B virus lineages.

Methods

Ferrets were infected and then challenged 3, 10, or 28 days later with pairs of influenza B/Victoria and B/Yamagata viruses.

Results

Viral interference occurred at challenge intervals of 3 and 10 days and occasionally at 28 days. At the longer interval, shedding of challenge virus was reduced, and this correlated with cross-reactive interferon γ responses from lymph nodes from virus-infected animals. Viruses from both lineages could prevent or significantly limit subsequent infection with a virus from the other lineage. Coinfections were rare, indicating the potential for reassortment between lineages is limited.

Conclusions

These data suggest that innate and cross-reactive immunity mediate viral interference and that this may contribute to the dominance of a specific influenza B virus lineage in any given influenza season. Furthermore, infection with one influenza B virus lineage may be beneficial in protecting against subsequent infection with either influenza B virus lineage.

A pharmacologically immunosuppressed mouse model for assessing influenza B virus pathogenicity and oseltamivir treatment

Immunocompromised patients are highly susceptible to influenza virus infections. Although neuraminidase inhibitor (NAI) therapy has proved effective in these patients, the treatment regimens require optimization, which can be partly addressed via animal models. Here, we describe a pharmacologically immunosuppressed mouse model for studying the pathogenesis of influenza B viruses and evaluating the efficacy of antiviral treatment. We modeled clinical regimens for dexamethasone and cyclophosphamide to immunosuppress BALB/c mice that were then inoculated with B/Phuket/3073/2013 (Yamagata lineage) or B/Brisbane/60/2008 (BR/08, Victoria lineage) virus. Although both viruses caused morbidity and mortality in immunosuppressed mice, BR/08 was more virulent, consistently inducing greater morbidity and 100% lethality in mice inoculated with at least 10³ TCID₅₀/mouse. The replication of both viruses was prolonged in the lungs of immunosuppressed mice, but the extent of pulmonary inflammation in these mice was markedly less than that in immunocompetent animals. Most of the examined cytokines, including IFN-γ, IL-1β, and RANTES, were significantly decreased in the lungs of immunosuppressed mice, as compared to immunocompetent animals, until at least 10 days post-infection. Treatment with the NAI oseltamivir for 8 or 16 days increased the mean survival time and reduced virus spread in the lungs of immunosuppressed mice challenged with a lethal dose of BR/08 but did not completely provide protection or decrease the virus titers. Our data suggests that the synergy of the viral load and aberrant immune responses is a key contributor to the severity of infection, as well as the limited efficacy of oseltamivir, which in immunosuppressed mice curtails virus release without clearing infected cells.

Epidemiology of influenza B in Australia: 2001-2014 influenza seasons

Background

Influenza B is characterised by two antigenic lineages: B/Victoria and B/Yamagata. These lineages circulate together with influenza A during influenza seasons, with varying incidence from year to year and by geographic region.

Objective

To determine the epidemiology of influenza B relative to influenza A in Australia.

Methods

Laboratory‐confirmed influenza notifications between 2001 and 2014 in Australia were obtained from the Australian National Notifiable Diseases Surveillance System.

Results

A total of 278 485 laboratory‐confirmed influenza cases were notified during the study period, comprising influenza A (82.2%), B (17.1%) and ‘other and untyped’ (0.7%). The proportion of notifications that were influenza B was highest in five‐ to nine‐year‐olds (27.5%) and lowest in persons aged 85 years and over (11.5%). Of all B notifications with lineage determined, 77.1% were B/Victoria and 22.9% were B/Yamagata infections. Mismatches between the dominant B lineage in a season and the trivalent vaccine B lineage occurred in over one‐third of seasons during the study years. In general, influenza B notifications peaked later than influenza A notifications.

Conclusion

The proportion of circulating influenza B in Australia during 2001‐2014 was slightly lower than the global average and was dominated by B/Victoria. Compared with influenza A, influenza B infection was more common among older children and young adults and less common in the very elderly. Influenza B lineage mismatch with the trivalent vaccine occurred about one‐third of the time.

Competitive Fitness of Influenza B Viruses Possessing E119A and H274Y Neuraminidase Inhibitor Resistance-Associated Substitutions in Ferrets

Neuraminidase (NA) inhibitors (NAIs) are the only antiviral drugs recommended for influenza treatment and prophylaxis. Although NAI-resistant influenza B viruses that could pose a threat to public health have been reported in the field, their fitness is poorly understood. We evaluated in ferrets the pathogenicity and relative fitness of reverse genetics (rg)-generated influenza B/Yamanashi/166/1998-like viruses containing E119A or H274Y NA substitutions (N2 numbering). Ferrets inoculated with NAI-susceptible rg-wild-type (rg-WT) or NAI-resistant (rg-E119A or rg-H274Y) viruses developed mild infections. Growth of rg-E119A virus in the nasal cavities was delayed, but the high titers at 3 days post-inoculation (dpi) were comparable to those of the rg-WT and rg-H274Y viruses (3.6-4.1 log10TCID50/mL). No virus persisted beyond 5 dpi and replication did not extend to the trachea or lungs. Positive virus antigen-staining of the nasal turbinate epithelium was intermittent with the rg-WT and rg-H274Y viruses; whereas antigen-staining for the rg-E119A virus was more diffuse. Virus populations in ferrets coinoculated with NAI-susceptible and -resistant viruses (1:1 mixture) remained heterogeneous at 5 dpi but were predominantly rg-WT (>70%). Although the E119A substitution was associated with delayed replication in ferrets, the H274Y substitution did not measurably affect viral growth properties. These data suggest that rg-H274Y has undiminished fitness in single virus inoculations, but neither rg-E119A nor rg-H274Y gained a fitness advantage over rg-WT in direct competition experiments without antiviral drug pressure. Taken together, our data suggest the following order of relative fitness in a ferret animal model: rg-WT > rg-H274Y > rg-E119A.

Impact of quadrivalent influenza vaccine on public health and influenza-related costs in Australia

BACKGROUND

Annual trivalent influenza vaccines (TIV) containing three influenza strains (A/H1N1, A/H3N2, and one B) have been recommended for the prevention of influenza. However, worldwide co-circulation of two distinct B lineages (Victoria and Yamagata) and difficulties in predicting which lineage will predominate each season have led to the development of quadrivalent influenza vaccines (QIV), which include both B lineages. Our analysis evaluates the public health benefit and associated influenza-related costs avoided which would have been obtained by using QIV rather than TIV in Australia over the period 2002-2012.

METHODS

A static model stratified by age group was used, focusing on people at increased risk of influenza as defined by the Australian vaccination recommendations. B-lineage cross-protection was accounted for. We calculated the potential impact of QIV compared with TIV over the seasons 2002-2012 (2009 pandemic year excluded) using Australian data on influenza circulation, vaccine coverage, hospitalisation and mortality rates as well as unit costs, and international data on vaccine effectiveness, influenza attack rate, GP consultation rate and working days lost. Third-party payer and societal influenza-related costs were estimated in 2014 Australian dollars. Sensitivity analyses were conducted.

RESULTS

Using QIV instead of TIV over the period 2002-2012 would have prevented an estimated 68,271 additional influenza cases, 47,537 GP consultations, 3,522 hospitalisations and 683 deaths in the population at risk of influenza. These results translate into influenza-related societal costs avoided of $46.5 million. The estimated impact of QIV was higher for young children and the elderly. The overall impact of QIV depended mainly on vaccine effectiveness and the influenza attack rate attributable to the mismatched B lineage.

CONCLUSION

The broader protection offered by QIV would have reduced the number of influenza infections and its related complications, leading to substantial influenza-related costs avoided.

Trivalent and quadrivalent influenza vaccination effectiveness in Australia and South Africa: results from a modelling study

BACKGROUND

A modelling study was conducted to determine the effectiveness of trivalent (TIV) and quadrivalent (QIV) vaccination in South Africa and Australia.

OBJECTIVES

This study aimed to determine the potential benefits of alternative vaccination strategies which may depend on community-specific demographic and health characteristics.

METHODS

Two influenza A and two influenza B strains were simulated using individual-based simulation models representing specific communities in South Africa and Australia over 11 years. Scenarios using TIV or QIV, with alternative prioritisation strategies and vaccine coverage levels, were evaluated using a country-specific health outcomes process.

RESULTS

In South Africa, approximately 18% fewer deaths and hospitalisations would be expected to result from the use of QIV compared to TIV over the 11 modelled years (P = 0·031). In Australia, only 2% (P = 0·30) fewer deaths and hospitalisations would result. Vaccinating 2%, 5%, 15% or 20% of the population with TIV using a strategy of prioritising vulnerable age groups, including HIV-positive individuals, resulted in reductions in hospitalisations and mortality of at least 7%, 18%, 57% and 66%, respectively, in both communities.

CONCLUSIONS

The degree to which QIV can reduce health burden compared to TIV is strongly dependent on the number of years in which the influenza B lineage in the TIV matches the circulating B lineages. Assuming a moderate level of B cross-strain protection, TIV may be as effective as QIV. The choice of vaccination prioritisation has a greater impact than the QIV/TIV choice, with strategies targeting those most responsible for transmission being most effective.

Ten influenza seasons in France: distribution and timing of influenza A and B circulation, 2003-2013

BACKGROUND

Describing the circulation of influenza viruses and the characteristics of seasonal epidemics remains an essential tool to optimize the strategies of influenza prevention and control. Special attention has been recently paid to influenza B in the context of the availability of a quadrivalent vaccine, containing two influenza B strains.

METHODS

We used data from a practitioners-based influenza surveillance network to describe the circulation of influenza viruses in France from 2003-2004 to 2012-2013. Nasopharyngeal swabs taken from acute respiratory infection (ARI) patients between October and April were tested for influenza. We reported the number of influenza cases by virus type (A, B), subtype (A(H1), A(H3)) and B lineage (Yamagata, Victoria) in each season and determined the frequency of influenza B vaccine mismatch. We estimated weekly incidence of influenza by extrapolating reported influenza cases to the French population. We compared the temporal characteristics of the epidemics caused by influenza A(H1), A(H3) and B.

RESULTS

Overall, 49,919 ARI patients were tested, of which 16,287 (32.6 %) were positive for influenza. Type B virus caused 23.7 % of all influenza cases. Virus subtypes A(H1) and A(H3) caused 51.6 % and 48.4 % of influenza A cases, respectively. Viruses of the B-Yamagata and B-Victoria lineage caused 62.8 % and 37.2 % of influenza B cases, respectively. There was an influenza B vaccine mismatch in three of the five seasons where influenza B caused 10 % or more of all influenza cases. Influenza A(H3) had the highest average value of estimated weekly incidence during the study period. Influenza B peaked an average 3.8 weeks later than influenza A when both virus types were circulating. No differences in the duration of influenza A and B epidemics were observed.

CONCLUSIONS

Influenza A(H3) was the most prevalent influenza type during the study period. Influenza B caused around one fourth of all influenza cases and tended to circulate later than influenza A. The frequency of influenza B vaccine mismatches was substantial. Timely data on the circulation of influenza viruses collected within influenza surveillance systems are essential to optimize influenza prevention and control strategies.

Competitive fitness of influenza B viruses with neuraminidase inhibitor-resistant substitutions in a coinfection model of the human airway epithelium

Influenza A and B viruses are human pathogens that are regarded to cause almost equally significant disease burdens. Neuraminidase (NA) inhibitors (NAIs) are the only class of drugs available to treat influenza A and B virus infections, so the development of NAI-resistant viruses with superior fitness is a public health concern. The fitness of NAI-resistant influenza B viruses has not been widely studied. Here we examined the replicative capacity and relative fitness in normal human bronchial epithelial (NHBE) cells of recombinant influenza B/Yamanashi/166/1998 viruses containing a single amino acid substitution in NA generated by reverse genetics (rg) that is associated with NAI resistance. The replication in NHBE cells of viruses with reduced inhibition by oseltamivir (recombinant virus with the E119A mutation generated by reverse genetics [rg-E119A], rg-D198E, rg-I222T, rg-H274Y, rg-N294S, and rg-R371K, N2 numbering) or zanamivir (rg-E119A and rg-R371K) failed to be inhibited by the presence of the respective NAI. In a fluorescence-based assay, detection of rg-E119A was easily masked by the presence of NAI-susceptible virus. We coinfected NHBE cells with NAI-susceptible and -resistant viruses and used next-generation deep sequencing to reveal the order of relative fitness compared to that of recombinant wild-type (WT) virus generated by reverse genetics (rg-WT): rg-H274Y > rg-WT > rg-I222T > rg-N294S > rg-D198E > rg-E119A ≫ rg-R371K. Based on the lack of attenuated replication of rg-E119A in NHBE cells in the presence of oseltamivir or zanamivir and the fitness advantage of rg-H274Y over rg-WT, we emphasize the importance of these substitutions in the NA glycoprotein. Human infections with influenza B viruses carrying the E119A or H274Y substitution could limit the therapeutic options for those infected; the emergence of such viruses should be closely monitored.

IMPORTANCE

Influenza B viruses are important human respiratory pathogens contributing to a significant portion of seasonal influenza virus infections worldwide. The development of resistance to a single class of available antivirals, the neuraminidase (NA) inhibitors (NAIs), is a public health concern. Amino acid substitutions in the NA glycoprotein of influenza B virus not only can confer antiviral resistance but also can alter viral fitness. Here we used normal human bronchial epithelial (NHBE) cells, a model of the human upper respiratory tract, to examine the replicative capacities and fitness of NAI-resistant influenza B viruses. We show that virus with an E119A NA substitution can replicate efficiently in NHBE cells in the presence of oseltamivir or zanamivir and that virus with the H274Y NA substitution has a relative fitness greater than that of the wild-type NAI-susceptible virus. This study is the first to use NHBE cells to determine the fitness of NAI-resistant influenza B viruses.

Animal models for influenza viruses: implications for universal vaccine development

Influenza virus infections are a significant cause of morbidity and mortality in the human population. Depending on the virulence of the influenza virus strain, as well as the immunological status of the infected individual, the severity of the respiratory disease may range from sub-clinical or mild symptoms to severe pneumonia that can sometimes lead to death. Vaccines remain the primary public health measure in reducing the influenza burden. Though the first influenza vaccine preparation was licensed more than 60 years ago, current research efforts seek to develop novel vaccination strategies with improved immunogenicity, effectiveness, and breadth of protection. Animal models of influenza have been essential in facilitating studies aimed at understanding viral factors that affect pathogenesis and contribute to disease or transmission. Among others, mice, ferrets, pigs, and nonhuman primates have been used to study influenza virus infection in vivo, as well as to do pre-clinical testing of novel vaccine approaches. Here we discuss and compare the unique advantages and limitations of each model.

Inactivated quadrivalent split-virus seasonal influenza vaccine (Fluarix® quadrivalent): a review of its use in the prevention of disease caused by influenza A and B

The inactivated quadrivalent split-virus seasonal influenza vaccine [Fluarix® quadrivalent, manufactured in Dresden (D-QIV)] contains 15 μg haemagglutinin from each of the four influenza virus strains expected to circulate in the upcoming influenza season. Unlike seasonal trivalent influenza vaccines (TIVs), which have been used previously, quadrivalent influenza vaccines (QIVs) contain two influenza A subtype viruses and two B type viruses. As two different B viruses have co-circulated in recent years, incorporating both B lineages reduces the risk of the dominant B strain not being included in the vaccine. D-QIV is approved for active immunization of individuals aged ≥3 years to prevent disease caused by the influenza A subtype viruses and B type viruses contained in the vaccine. In large randomized, controlled trials, D-QIV was highly immunogenic in healthy adults (including individuals aged ≥65 years) and children, and exceeded the criteria for vaccine licensure. Immune responses for D-QIV, compared with those for TIVs, were non-inferior against influenza A strains and common B strains and superior against the additional B strain. D-QIV was generally well tolerated in all age groups studied and, overall, reactogenicity and tolerability were generally similar to observations with TIVs. Quadrivalent influenza vaccines are expected to offer substantial cost-effectiveness benefits in seasons where the B lineage selected for inclusion in TIVs does not match the dominant circulating strain. Thus, by incorporating both circulating influenza B lineages, vaccination with D-QIV is likely to reduce the risk of the dominant circulating B type virus not matching the strain selected for the vaccine and, therefore, more effectively protect target populations from influenza than TIVs.

Key issues and challenges in estimating the impact and cost-effectiveness of quadrivalent influenza vaccination

Evidence has shown that quadrivalent influenza vaccines containing all four subtypes are safe and immunogenic. However, to date there have been few published studies exploring the population-level clinical and economic impact of quadrivalent compared to trivalent influenza vaccines. Economic evaluation studies need to be conducted in order to inform country-level decision making about whether (and how to) introduce and replace the current trivalent influenza vaccines with quadrivalent influenza vaccination programs. Several key issues associated with estimating the clinical and economic impact of the trivalent versus quadrivalent vaccines are discussed in this article, particularly the complexities involved in estimating the incremental preventable disease and economic burden. Other factors, such as the indirect (herd) protection from quadrivalent influenza vaccination and the timing of the replacement of trivalent influenza vaccination programs are also discussed.

Prevention and Control of Influenza Viruses

The 2003–2004 outbreaks of highly pathogenic avian influenza (HPAI) have proven to be disastrous to the regional poultry industry in Asia, and have raised serious worldwide public health apprehension regarding the steps that should be taken to urgently control HPAI. Control measures must be taken based on the principles of biosecurity and disease management and at the same time making public aware of the precautionary measures at the verge of outbreak. Creation of protection and surveillance zones, various vaccination strategies viz. routine, preventive, emergency, mass and targeted vaccination programmes using live, inactivated and recombinant vaccines are the common strategies adopted in different parts of the globe. The new generation vaccines include recombinant vaccines and recombinant fusion vaccine. The pro-poor disease control programmes, giving compensation and subsidies to the farmers along with effective and efficient Veterinary Services forms integral part of control of HPAI. Following biosecurity principles and vaccination forms integral part of control programme against swine and equine influenza as well. Use of neuraminidase (NA) inhibitors (Zanamivir and Oseltamivir) for the treatment of human influenza has been widely accepted worldwide. The threat of increasing resistance of the flu viruses to these antivirals has evoked interest in the development of novel antiviral drugs for influenza virus such as inhibitors of cellular factors and host signalling cascades, cellular miRNAs, siRNA and innate immune peptides (defensins and cathelicidins). Commercial licensed inactivated vaccines for humans against influenza A and B viruses are available consisting of three influenza viruses: influenza type A subtype H3N2, influenza type A subtype H1N1 (seasonal) virus strain and influenza type B virus strain. As per WHO, use of tetravaccine consisting of antigens of influenza virus serotypes H3N2, H1N1, B and H5 is the most promising method to control influenza pandemic. All healthy children in many countries are required to be vaccinated between 6 and 59 months of age. The seasonal vaccines currently used in humans induce strain-specific humoral immunity as the antibodies. Universal influenza virus vaccines containing the relatively conserved ectodomain of M2 (M2e), M1, HA fusion peptide and stalk domains, NA, NP alone or in combination have been developed which have been shown to induce cross-protection. The T cell-based vaccines are another recent experimental approach that has been shown to elicit broad-spectrum heterosubtypic immunity in the host. As far as HPAI is concerned, various pandemic preparedness strategies have been documented.

The evolving history of influenza viruses and influenza vaccines

The isolation of influenza virus 80 years ago in 1933 very quickly led to the development of the first generation of live-attenuated vaccines. The first inactivated influenza vaccine was monovalent (influenza A). In 1942, a bivalent vaccine was produced after the discovery of influenza B. It was later discovered that influenza viruses mutated leading to antigenic changes. Since 1973, the WHO has issued annual recommendations for the composition of the influenza vaccine based on results from surveillance systems that identify currently circulating strains. In 1978, the first trivalent vaccine included two influenza A strains and one influenza B strain. Currently, there are two influenza B lineages circulating; in the latest WHO recommendations, it is suggested that a second B strain could be added to give a quadrivalent vaccine. The history of influenza vaccine and the associated technology shows how the vaccine has evolved to match the evolution of influenza viruses.

Neuraminidase inhibitors for influenza B virus infection: efficacy and resistance

Many aspects of the biology and epidemiology of influenza B viruses are far less studied than for influenza A viruses, and one of these aspects is efficacy and resistance to the clinically available antiviral drugs, the neuraminidase (NA) inhibitors (NAIs). Acute respiratory infections are one of the leading causes of death in children and adults, and influenza is among the few respiratory infections that can be prevented and treated by vaccination and antiviral treatment. Recent data has suggested that influenza B virus infections are of specific concern to pediatric patients because of the increased risk of severe disease. Treatment of influenza B is a challenging task for the following reasons: This review presents current knowledge of the efficacy of NAIs for influenza B virus and antiviral resistance in clinical, surveillance, and experimental studies.

The use of pyrosequencer-generated sequence-signatures to identify the influenza B-lineage and the subclade of the B/Yamataga-lineage viruses from currently circulating human influenza B viruses

BACKGROUND

Influenza B viruses belong to two antigenically and genetically distinct lineages which co-circulate in varying proportions in many countries.

OBJECTIVE

To develop simple, rapid, accurate and robust methods to detect and differentiate currently circulating B-lineage viruses in respiratory samples and virus isolates.

STUDY DESIGN

Haemagglutinin (HA) gene sequences from more than 6300 influenza B strains were analysed to identify signature sequences that could be used to distinguish between B-lineages and sublineages.

RESULTS

Pyrosequencing and a real time PCR assays were developed to detect the major B-lineages (B/Victoria/2/87 or B/Yamagata/16/88) and pyrosequencing for a unique mutation was used to further differentiate the B/Yamagata viruses into two currently co-circulating subgroups. More than 300 influenza virus-containing samples, including original specimens, cell and egg grown viruses, were tested with a 100% accuracy. Furthermore, when the same PCR primers were used in an rRT-PCR assay, the two lineages could be differentiated by their distinct ranges of melting temperature with an overall accuracy of 99% for 158 samples tested.

CONCLUSIONS

These new pyrosequencing and rRT-PCR methods have the potential to aid the rapid identification of influenza B-lineages for surveillance purposes and to increase the available data for bi-annual selection of viruses for updating influenza vaccines.