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

Analysis of factors influencing influenza outbreaks in schools in Taicang City, China

Objective

This study aims to analyze the awareness of influenza prevention and control and the behavioral attitudes toward the work among parents and staff in schools in Taicang City and the impact of the vaccination rate among students on influenza outbreaks in schools. The findings can provide references for the development of effective control strategies for the spread of influenza.

Methods

An anonymous questionnaire survey was conducted on 10,962 students from 20 schools in Taicang City, with class as the unit of analysis. The survey investigated their awareness of influenza prevention and control, their attitudes, and the vaccination coverage.

Results

From January to June 2023, a total of 388 influenza outbreaks were reported in schools in Taicang City, involving 77 schools. There were 3,475 confirmed cases, with an average infection rate of 18.53%. In schools where influenza outbreaks had occurred, the incidence rate of those who received influenza vaccine was significantly lower than those who did not, and the vaccine protection rate was 28.22%. The knowledge awareness rates of "the main transmission routes of influenza" and "influenza vaccination can prevent influenza" among parents of students were 95.49 and 93.16%, respectively. The differences between schools involved in the epidemic and non-epidemic were statistically significant (p < 0.05). The correct attitudes of parents toward "actively reporting relevant symptoms to teachers when their children show symptoms" and "avoiding classes with diseases when their children are suspected to be sick" are 98.80 and 96.26%, respectively. The differences between schools with and without epidemic are statistically significant (p < 0.05). The correct attitudes of the class teacher toward "correct management and control of students with flu like symptoms in the class" and "taking correct prevention and control measures in the event of a flu epidemic in the class" were 89.36 and 92.55%, respectively. The differences between epidemic related and non-epidemic related classes were statistically significant (p < 0.05).

Conclusion

Enhance the knowledge level of influenza prevention and control among parents of students, Strengthening the training for class teachers in emergency response to infectious diseases and increasing vaccination coverage among students can effectively reduce the incidence of influenza and thereby the occurrence of cluster outbreaks in schools.

Differentiation of influenza B lineages circulating in different regions of Brazil, 2014 – 2016, using molecular assay

Background

Two antigenically and genetically distinct lineages of influenza B viruses (B/Victoria and B/Yamagata) have been co-circulating worldwide since 2002. Virological surveillance is essential to differentiate between both lineages with a view to the annual updating of the B component for the trivalent or quadrivalent influenza vaccine composition.

Methods

The samples analyzed in the present study were collected by influenza sentinel units located in the Southeast, Midwest, North, and Northeast regions of Brazil, part of the National Influenza Virus Surveillance Network, coordinated by the Ministry of Health of Brazil. A total of 870 influenza B positive samples by reverse transcription real – time polymerase chain reaction (RT-qPCR), collected during 2014, 2015, and 2016 influenza seasons, were submitted to the influenza B lineage genotyping panel for characterization as B/Yamagata or Victoria lineages using RT-qPCR.

Results

Of the 197 samples analyzed in 2014, a total of 160 (81 %) corresponded to the B/Yamagata lineage, 19 (10 %) to the B/Victoria lineage, and 18 (9 %) to indeterminate lineages. Of the 190 samples analyzed in 2015, a total of 124 (65 %) corresponded to the B/Yamagata lineage; 55 (29 %) to the B/Victoria lineage, whereas 11 (6 %) were of indeterminate lineages. Of the 483 samples analyzed in 2016, a total of 297 (62 %) corresponded to the B /Victoria lineage; 174 (36 %) to the B/Yamagata lineage and 12 (2 %) to indeterminate lineages. This cross-sectional study revealed influenza B virus (IBV) infection in all age groups, and among them, the highest prevalence was observed in individuals between 11 and 49 years of age Our findings demonstrate the match between influenza B virus lineages recommended by the World Health Organization (WHO) for the trivalent vaccine composition to be used in the Southern Hemisphere (SH) and the predominant circulating viruses during the 2014, 2015, and 2016 seasons.

Epidemiology and Molecular Analyses of Influenza B Viruses in Senegal from 2010 to 2019

Influenza virus types A and B are responsible for acute viral infections that affect annually 1 billion people, with 290,000 to 650,000 deaths worldwide. In this study, we investigated the circulation of influenza B viruses over a 10-year period (2010–2019). Specimens from patients suspected of influenza infection were collected. Influenza detection was performed following RNA extraction and real-time RT-PCR. Genes coding for hemagglutinin (HA) and neuraminidase (NA) of influenza B viruses were partially sequenced, and phylogenetic analyses were carried out subsequently. During the study period, we received and tested a total of 15,156 specimens. Influenza B virus was detected in 1322 (8.7%) specimens. The mean age of influenza B positive patients was 10.9 years. When compared to reference viruses, HA genes from Senegalese circulating viruses showed deletions in the HA1 region. Phylogenetic analysis highlighted the co-circulation of B/Victoria and B/Yamagata lineage viruses with reassortant viruses. We also noted a clear seasonal pattern of circulation of influenza B viruses in Senegal.

Modelling the influenza disease burden in people aged 50-64 and ≥65 years in Australia

BACKGROUND

Estimation of influenza disease burden is necessary to monitor the impact of intervention programmes. This study aims to estimate the attributable fraction of respiratory and circulatory disease due to influenza among Australian adults 50-64 and ≥65 years of age.

METHODS

A semi-parametric generalised-additive model was used to estimate annual and average rate of influenza-attributable hospitalisation and death per 100,000 population under the principal diagnosis of influenza/pneumonia, respiratory, circulatory and myocardial infarction (MI) from 2001 through 2017.

RESULTS

Over the study period, seasonal influenza accounted for an estimated annual average respiratory hospitalisation rate of 78.9 (95%CI: 76.3, 81.4) and 287.5 (95%CI: 279.8, 295.3) per 100,000 population in adults aged 50-64 and ≥65 years, respectively. The corresponding respiratory mortality rates were 0.9 (95%CI: 0.7, 1.2) and 18.2 (95%CI: 16.9, 19.4) per 100,000 population. The 2017 season had the highest influenza-attributable respiratory hospitalisations in both age groups, and respiratory complications were estimated approximately 2.5 times higher than the average annual estimate in adults aged ≥65 years in 2017. For mortality, on average, influenza attributed 1,080 circulatory and 361 MI deaths in adults aged ≥65 years per year. Influenza accounted for 1% and 2.8% of total MI deaths in adults aged 50-64 and ≥65 years, respectively.

CONCLUSION

Rates of cardiorespiratory morbidity and mortality were high in older adults, whilst the younger age group contributed a lower disease burden. Extension of influenza vaccination programme beyond the targeted population could be an alternative strategy to reduce the burden of influenza.

Burden of Seasonal Influenza A and B in Panama from 2011 to 2017: An Observational Retrospective Database Study

Introduction

Influenza A and B viruses constantly evolve and cause seasonal epidemics and sporadic outbreaks. Therefore, epidemiological surveillance is critical for monitoring their circulation pattern. Trivalent and quadrivalent vaccine formulations are available in Panama (until and since 2016, respectively). Herein, we analysed influenza A and B epidemiological patterns in Panama.

Methods

This was a retrospective descriptive analysis of all laboratory-confirmed influenza nasopharyngeal samples recorded between 2011 and 2017 in the nationwide surveillance database of Gorgas Memorial Institute for Health Studies. The analysis involved data relative to demographic information, virus type, subtype and lineage, geographic region, treatment and outcomes. The percentage level of mismatch between circulating and vaccine-recommended B lineage was assessed for each May–October influenza season.

Results

Among 1839 influenza cases, 79.6% were type A and 20.4% were type B. Most of them were observed in Panama City (54.7%) followed by the West (23.2%) and Central (16.7%) regions; across all regions, influenza A and B cases were distributed in a 4:1 ratio. Overall, approximately half were hospitalized (52.0% for type A; 45.5% for type B) and 11 (0.6%) died. Treatment, usually antimicrobial, was administered in 15.1% of cases. Children less than 2 years old were the most affected by this disease. Influenza type A circulated every year, while influenza B only circulated in 2012, 2014 and 2017. In the 2012 May–October influenza B season, the predominant lineage was B/Victoria and a switch to B/Yamagata was observed in 2014. Both lineages co-circulated in 2017, leading to a 38.9% B-lineage-level vaccine mismatch.

Conclusion

Influenza A was predominant among all ages and children less than 2 years and inhabitants of Panama City reported the highest circulation rate. In 2017, co-circulation of both B lineages led to a vaccine mismatch. Continuous monitoring of seasonal influenza is critical to establish immunization recommendations.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40121-021-00501-y.

Influenza or “flu” is caused by influenza viruses A and B and its symptoms range from mild to severe. This virus is constantly evolving; thus, careful monitoring of influenza is important to update immunization and vaccine recommendations yearly. This study used data from surveillance centres in Panama from 2011 to 2017 and evaluated the number of flu cases by age, gender, region, virus type, symptoms, comorbidities, treatment, coinfections with other viruses, and the circulating influenza subtype and the vaccine recommended each year. We found several points: almost 80% of cases were influenza A; most of the positive samples were found in children less than 2 years old and the Panama city region; more than 50% of influenza cases needed hospitalization; and in 2017 a mismatch was detected between the circulating influenza subtype and the recommended vaccine. This study helped to better characterize influenza circulation patterns and the burden of the disease during 2011–2017. We concluded that continuous monitoring of the influenza cases is necessary to establish future vaccination recommendations.

Substantial effect of phytochemical constituents against the pandemic disease influenza-a review

Background

Influenza is an acute respiratory tract infection caused by the influenza virus. Vaccination and antiviral drugs are the two methods opted to control the disease. Besides their efficiency, they also cause adverse side effects. Hence, scientists turned their attention to powerful herbal medicines. This review put focus on various proven, scientifically validated anti-influenza compounds produced by the plants suggested for the production of newer drugs for the better treatment of influenza and its related antiviral diseases too.

Main body

In this review, fifty medicinal herb phytochemical constituents and their anti-influenza activities have been documented. Specifically, this review brings out the accurate and substantiates mechanisms of action of these constituents. This study categorizes the phytochemical constituents into primary and secondary metabolites which provide a source for synthesizing and developing new drugs.

Conclusion

This article provides a summary of the actions of the herbal constituents. Since the mechanisms of action of the components are elucidated, the pandemic situation arising due to influenza and similar antiviral diseases can be handled promisingly with greater efficiency. However, clinical trials are in great demand. The formulation of usage may be a single drug compound or multi-herbal combination. These, in turn, open up a new arena for the pharmaceutical industries to develop innovative drugs.

Ten Years of National Seasonal Surveillance for Severe Complications of Influenza in Australian Children

BACKGROUND

Severe complications of influenza in children are uncommon but may result in admission to hospital or an intensive care unit (ICU) and death.

METHODS

Active prospective surveillance using the Australian Paediatric Surveillance Unit with monthly reporting by pediatricians of national demographic and clinical data on children with <15 years of age hospitalized with severe complications of laboratory-confirmed influenza during ten influenza seasons 2008-2017.

RESULTS

Of 722 children notified, 613 had laboratory-confirmed influenza and at least one severe complication. Most (60%) were <5 years of age; 10% were <6 months, hence ineligible for vaccination. Almost half of all cases were admitted to ICU and 30 died. Most children were previously healthy: 40.3% had at least one underlying medical condition. Sixty-five different severe complications were reported; pneumonia was the most common, occurring in over half of all cases. Influenza A accounted for 68.6% hospitalizations; however, influenza B was more often associated with acute renal failure (P = 0.014), rhabdomyolysis (P = 0.019), myocarditis (P = 0.015), pericarditis (P = 0.013), and cardiomyopathy (P = 0.035). Children who died were more likely to be older (5-14 years), have underlying medical conditions, be admitted to ICU, and have encephalitis, acute renal failure, or myocarditis. Only 36.1% of all children reported received antiviral medications, and 8.5% were known to be vaccinated for seasonal influenza.

CONCLUSIONS

Severe influenza complications cause morbidity and mortality in children, which may increase if coinfection with COVID-19 occurs in the 2020 season and beyond. Increased vaccination rates, even in healthy children, early diagnosis and timely antiviral treatment are needed to reduce severe complications and death.

Evidence for an increase in the intensity of inter-seasonal influenza, Queensland, Australia, 2009-2019

BACKGROUND

Inter-seasonal influenza cases have been increasing in Australia. Studies of influenza seasonality typically focus on seasonal transmission in temperate regions, leaving our understanding of inter-seasonal epidemiology limited. We aimed to improve understanding of influenza epidemiology during inter-seasonal periods across climate zones, and explored influenza intensity and strain dominance patterns over time.

METHODS

Queensland state-wide laboratory-confirmed influenza notifications and public laboratory influenza test data from 2009-2019 were described by demographics, time period, region and strain type. We compared influenza intensity over time using the WHO Average Curve method to provide thresholds for seasonal and inter-seasonal periods.

RESULTS

Among the 243 830 influenza notifications and 490 772 laboratory tests reported in Queensland between 2009 and 2019, 15% of notifications and 40% of tests occurred during inter-seasonal periods, with 6.3% of inter-seasonal tests positive. Inter-seasonal notifications and tests substantially increased over time and increases in weekly proportions positive and intensity classifications suggested gradual increases in virus activity. Tropical inter-seasonal activity was higher with periods of marked increase. Influenza A was dominant, although influenza B represented up to 72% and 42% of notifications during some seasonal and inter-seasonal periods, respectively.

CONCLUSIONS

Using notification and testing data, we have demonstrated a gradual increase in inter-seasonal influenza over time. Our findings suggest this increase results from an interplay between testing, activity and intensity, and strain circulation. Seasonal intensity and strain circulation appeared to modify subsequent period intensity. Routine year-round surveillance data would provide a better understanding of influenza epidemiology during this infrequently studied inter-seasonal time period.

Clinical characteristics and outcomes of influenza A and B virus infection in adult Australian hospitalised patients

BACKGROUND

Influenza B is often perceived as a less severe strain of influenza. The epidemiology and clinical outcomes of influenza B have been less thoroughly investigated in hospitalised patients. The aims of this study were to describe clinical differences and outcomes between influenza A and B patients admitted over a period of 4 years.

METHODS

We retrospectively collected data of all laboratory confirmed influenza patients ≥18 years at two tertiary hospitals in South Australia. Patients were confirmed as influenza positive if they had a positive polymerase-chain-reaction (PCR) test of a respiratory specimen. Complications during hospitalisation along with inpatient mortality were compared between influenza A and B. In addition, 30 day mortality and readmissions were compared. Logistic regression model compared outcomes after adjustment for age, Charlson index, sex and creatinine levels.

RESULTS

Between January 2016-March 2020, 1846 patients, mean age 66.5 years, were hospitalised for influenza. Of whom, 1630 (88.3%) had influenza A and 216 (11.7%) influenza B. Influenza B patients were significantly younger than influenza A. Influenza A patients were more likely be smokers with a history of chronic obstructive pulmonary disease (COPD) and ischaemic heart disease (IHD) than influenza B. Complications, including pneumonia and acute coronary syndrome (ACS) were similar between two groups, however, septic shock was more common in patients with influenza B. Adjusted analyses showed similar median length of hospital stay (LOS), in hospital mortality, 30-day mortality and readmissions between the two groups.

CONCLUSIONS

Influenza B is less prevalent and occurs mostly in younger hospitalised patients than influenza A. Both strains contribute equally to hospitalisation burden and complications.

TRIAL REGISTRATION

Australia and New Zealand Clinical Trial Registry (ANZCR) no ACTRN12618000451202 date of registration 28/03/2018.

Comparative epidemiology, phylogenetics, and transmission patterns of severe influenza A/H3N2 in Australia from 2003 to 2017

Background

Over the last two decades, Australia has experienced four severe influenza seasons caused by a predominance of influenza A (A/H3N2): 2003, 2007, 2012, and 2017.

Methods

We compared the epidemiology, genetics, and transmission dynamics of severe A/H3N2 seasons in Australia from 2003 to 2017.

Results

Since 2003, the proportion of notifications in 0‐4 years old has decreased, while it has increased in the age group >80 years old (P < .001). The genetic diversity of circulating influenza A/H3N2 viruses has also increased over time with the number of single nucleotide polymorphisms significantly (P < .05) increasing. We also identified five residue positions within or near the receptor binding site of HA (144, 145, 159, 189, and 225) undergoing frequent mutations that are likely involved in significant antigenic drift and possibly severity. The Australian state of Victoria was identified as a frequent location for transmission either to or from other states and territories over the study years. The states of New South Wales and Queensland were also frequently implicated as locations of transmission to other states and territories but less so over the years. This indicates a stable but also changing dynamic of A/H3N2 circulation in Australia.

Conclusion

These results have important implications for future influenza surveillance and control policy in the country. Reasons for the change in age‐specific infection and increased genetic diversity of A/H3N2 viruses in recent years should be explored.

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.

Estimated hospitalisations attributable to seasonal and pandemic influenza in Australia: 2001- 2013

Background

Influenza continues to cause seasonal epidemics and pandemics in humans. The burden of influenza is underestimated by traditional laboratory-based surveillance, and modelled estimates are required for influenza-attributable morbidity and mortality. We aimed to estimate the influenza-attributable hospitalisation in Australia, by influenza type.

Methods

A generalised-additive regression model was used to estimate type- and age-specific influenza-attributable hospitalisation rates per 100,000 population by principal diagnosis in Australia, from 2001 through 2013. Weekly counts of laboratory-confirmed influenza notifications and by type, influenza A and B were used as covariates in the model. Main principal diagnosis categories of interest were influenza and pneumonia and respiratory admissions. A smoothing spline was used to control for unmeasured time varying factors. Results for 2009, in which the pandemic influenza A(H1N1)pdm09 virus circulated, were not included in annual averages and are reported separately.

Results

During the study period, the estimated annual average, all-age, annual respiratory hospitalisation rates attributable to seasonal influenza type A, B and total influenza were 45.4 (95% CI: 34.9, 55.9), 32.6 (95% CI: 22.8, 42.4), and 76.9 (95% CI: 73.6, 80.2) per 100,000 population, respectively. During 2009, the estimated total pandemic influenza-attributable, all-age, respiratory hospitalisation rate was 56.1 (95% CI: 47.4, 64.9) per 100,000. Older adults (≥85 years of age) experienced the highest influenza-attributable hospitalisation rates for both seasonal and 2009 pandemic influenza. Collinearity between influenza A and B time series in some years limited the ability of the model to resolve differences in influenza attribution between the two virus types.

Conclusion

Both seasonal and pandemic influenza caused considerable morbidity in Australia during the years studied, particularly among older adults. The pandemic hospitalisation rate in 2009 was lower than the average overall annual rate for seasonal influenza, but young to middle aged adults experience a hospitalisation rate similar to that of severe seasonal influenza.

Forecasting type-specific seasonal influenza after 26 weeks in the United States using influenza activities in other countries

To identify countries that have seasonal patterns similar to the time series of influenza surveillance data in the United States and other countries, and to forecast the 2018-2019 seasonal influenza outbreak in the U.S., we collected the surveillance data of 164 countries using the FluNet database, search queries from Google Trends, and temperature from 2010 to 2018. Data for influenza-like illness (ILI) in the U.S. were collected from the Fluview database. We identified the time lag between two time-series which were weekly surveillances for ILI, total influenza (Total INF), influenza A (INF A), and influenza B (INF B) viruses between two countries using cross-correlation analysis. In order to forecast ILI, Total INF, INF A, and INF B of next season (after 26 weeks) in the U.S., we developed prediction models using linear regression, auto regressive integrated moving average, and an artificial neural network (ANN). As a result of cross-correlation analysis between the countries located in northern and southern hemisphere, the seasonal influenza patterns in Australia and Chile showed a high correlation with those of the U.S. 22 weeks and 28 weeks earlier, respectively. The R2 score of ANN models for ILI for validation set in 2015-2019 was 0.758 despite how hard it is to forecast 26 weeks ahead. Our prediction models forecast that the ILI for the U.S. in 2018-2019 may be later and less severe than those in 2017-2018, judging from the influenza activity for Australia and Chile in 2018. It allows to estimate peak timing, peak intensity, and type-specific influenza activities for next season at 40th week. The correlation between seasonal influenza patterns in the U.S., Australia, and Chile could be used to forecast the next seasonal influenza pattern, which can help to determine influenza vaccine strategy approximately six months ahead in the U.S.

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 epidemiological signature of influenza B virus and its B/Victoria and B/Yamagata lineages in the 21st century

We describe the epidemiological characteristics, pattern of circulation, and geographical distribution of influenza B viruses and its lineages using data from the Global Influenza B Study. We included over 1.8 million influenza cases occurred in thirty-one countries during 2000–2018. We calculated the proportion of cases caused by influenza B and its lineages; determined the timing of influenza A and B epidemics; compared the age distribution of B/Victoria and B/Yamagata cases; and evaluated the frequency of lineage-level mismatch for the trivalent vaccine. The median proportion of influenza cases caused by influenza B virus was 23.4%, with a tendency (borderline statistical significance, p = 0.060) to be higher in tropical vs. temperate countries. Influenza B was the dominant virus type in about one every seven seasons. In temperate countries, influenza B epidemics occurred on average three weeks later than influenza A epidemics; no consistent pattern emerged in the tropics. The two B lineages caused a comparable proportion of influenza B cases globally, however the B/Yamagata was more frequent in temperate countries, and the B/Victoria in the tropics (p = 0.048). B/Yamagata patients were significantly older than B/Victoria patients in almost all countries. A lineage-level vaccine mismatch was observed in over 40% of seasons in temperate countries and in 30% of seasons in the tropics. The type B virus caused a substantial proportion of influenza infections globally in the 21^st century, and its two virus lineages differed in terms of age and geographical distribution of patients. These findings will help inform health policy decisions aiming to reduce disease burden associated with seasonal influenza.

Patterns of influenza B circulation in Latin America and the Caribbean, 2010-2017

OBJECTIVE

There are limited published data about the circulation of influenza B/Victoria and B/Yamagata in Latin America and the Caribbean (LAC) and most countries have a vaccine policy that includes the use of the trivalent influenza vaccine. We analyzed influenza surveillance data to inform decision-making in LAC about prevention strategies, such as the use of the quadrivalent influenza vaccine.

METHODS

There are a total of 28 reference laboratories and National Influenza Centers in LAC that conduct influenza virologic surveillance according to global standards, and on a weekly basis upload their surveillance data to the open-access World Health Organization (WHO) platform FluNet. These data include the number of specimens tested for influenza and the number of specimens positive for influenza by type, subtype and lineage, all by the epidemiologic week of specimen collection. We invited these laboratories to provide additional epidemiologic data about the hospitalized influenza B cases. We conducted descriptive analyses of patterns of influenza circulation and characteristics of hospitalized cases. We compared the predominant B lineage each season to the lineage in the vaccine applied, to determine vaccine mismatch. A Chi-square and Wilcoxan statistic were used to assess the statistical significance of differences in proportions and medians at the P<0.05 level.

FINDINGS

During 2010-2017, the annual number of influenza B cases in LAC was ~4500 to 7000 cases. Since 2011, among the LAC-laboratories reporting influenza B lineage using molecular methods, both B/Victoria and B/Yamagata were detected annually. Among the hospitalized influenza B cases, there were statistically significant differences observed between B/Victoria and B/Yamagata cases when comparing age and the proportion with underlying co-morbid conditions and with history of oseltamivir treatment (P<0.001). The proportion deceased among B/Victoria and B/Yamagata hospitalized cases did not differ significantly. When comparing the predominant influenza B lineage detected, as part of surveillance activities during 63 seasons among 19 countries, to the lineage of the influenza B virus included in the trivalent influenza vaccine used during that season, there was a vaccine mismatch noted during 32% of the seasons analyzed.

CONCLUSIONS

Influenza B is important in LAC with both B/Victoria and B/Yamagata circulating annually in all sub regions. During approximately one-third of the seasons, an influenza B vaccine mismatch was identified. Further analyses are needed to better characterize the medical and economic burden of each influenza B lineage, to examine the potential cross-protection of one vaccine lineage against the other circulating virus lineage, and to determine the potential impact and cost-effectiveness of using the quadrivalent vaccine rather than the trivalent influenza vaccine.

Universal influenza virus vaccines: what needs to happen next?

INTRODUCTION

Influenza occurs worldwide and causes significant disease burden in terms of morbidity, associated complications, hospitalizations, and deaths. Vaccination constitutes the primary approach for controlling influenza. Current influenza vaccines elicit a strain-specific response yet occasionally exhibit suboptimal effectiveness. This review describes the limits of available immunization tools and the future prospects and potentiality of universal influenza vaccines.

AREAS COVERED

New 'universal' vaccines, which are presently under development, are expected to overcome the problems related to the high variability of influenza viruses, such as the need for seasonal vaccine updates and re-vaccination. Here, we explore vaccines based on the highly conserved epitopes of the HA, NA, or extracellular domain of the influenza M2 protein, along with those based on the internal proteins such as NP and M1.

EXPERT OPINION

The development of a universal influenza vaccine that confers protection against homologous, drifted, and shifted influenza virus strains could obviate the need for annual reformulation and mitigate disease burden. The scientific community has long been awaiting the advent of universal influenza vaccines; these are currently under development in laboratories worldwide. If such vaccines are immunogenic, efficacious, and able to confer long-lasting immunity, they might be integrated with or supplant traditional influenza vaccines.

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

Introduction

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

Methods

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

Results

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

Conclusions

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

Broad and Protective Influenza B Virus Neuraminidase Antibodies in Humans after Vaccination and their Clonal Persistence as Plasma Cells

Although most seasonal inactivated influenza vaccines (IIV) contain neuraminidase (NA), the extent and mechanisms of action of protective human NA-specific humoral responses induced by vaccination are poorly resolved. Due to the propensity of influenza virus for antigenic drift and shift and its tendency to elicit predominantly strain-specific antibodies, humanity remains susceptible to waves of new strains of seasonal viruses and is at risk from viruses with pandemic potential for which limited or no immunity may exist. Here we demonstrate that the use of IIV results in increased levels of influenza B virus (IBV) NA-specific serum antibodies. Detailed analysis of the IBV NA B cell response indicates concurrent expansion of IBV NA-specific peripheral blood plasmablasts 7 days after IIV immunization which express monoclonal antibodies with broad and potent antiviral activity against both IBV Victoria and Yamagata lineages and prophylactic and therapeutic activity in mice. These IBV NA-specific B cell clonal lineages persisted in CD138+ long-lived bone marrow plasma cells. These results represent the first demonstration that IIV-induced NA human antibodies can protect and treat influenza virus infection in vivo and suggest that IIV can induce a subset of IBV NA-specific B cells with broad protective potential, a feature that warrants further study for universal influenza vaccine development.IMPORTANCE Influenza virus infections continue to cause substantial morbidity and mortality despite the availability of seasonal vaccines. The extensive genetic variability in seasonal and potentially pandemic influenza strains necessitates new vaccine strategies that can induce universal protection by focusing the immune response on generating protective antibodies against conserved targets such as regions within the influenza neuraminidase protein. We have demonstrated that seasonal immunization stimulates neuraminidase-specific antibodies in humans that are broad and potent in their protection from influenza B virus when tested in mice. These antibodies further persist in the bone marrow, where they are expressed by long-lived antibody-producing cells, referred to here as plasma cells. The significance in our research is the demonstration that seasonal influenza immunization can induce a subset of neuraminidase-specific B cells with broad protective potential, a process that if further studied and enhanced could aid in the development of a universal influenza vaccine.

Analysis of influenza B virus lineages and the HA1 domain of its hemagglutinin gene in Guangzhou, southern China, during 2016

Background

Few studies have analyzed influenza B virus lineages based on hemagglutinin A (HA) gene sequences in southern China. The present study analyzed the HA gene and the lineages of influenza B virus isolates from Guangzhou during 2016, and compared our results with the WHO-recommended vaccine strain.

Methods

Ninety patients with influenza B were recruited from the First Hospital of Guangzhou Medical University. Throat swab specimens of 72 patients had high viral loads. Among these 72 isolates, the HA1 domain of the HA gene in 43 randomly selected isolates was sequenced using reverse transcription-polymerase chain reaction (RT-PCR), and analyzed using MEGA 5.05.

Results

Eight of the 90 patients (8.9%) also had influenza A virus infections. Analysis of the 43 influenza B virus isolates indicated that 34 (79.1%) were from the Victoria lineage and 9 (20.9%) were from the Yamagata lineage. A comparison isolates in our Victoria lineage with the B/Brisbane/60/2008 strain indicated 12 mutation sites in the HA1 domain, 4 of which (I132V, N144D, C196S, and E198D) were in antigenic epitopes. A comparison of isolates in our Yamagata lineage with the B/Phuket/3073/2013 stain indicated 5 mutation sites in the HA1 domain, none of which was in an antigenic epitope. None of the isolates had a mutation in regions of the neuraminidase gene (NA) that are known to confer resistance to NA inhibitors.

Conclusion

In Guangzhou during 2016, most influenza B virus isolates were from the Victoria lineage, in contrast to the vaccine strain recommended by the WHO for this period.

Electronic supplementary material

The online version of this article (10.1186/s12985-018-1085-5) contains supplementary material, which is available to authorized users.

Cost-effectiveness of switching from trivalent to quadrivalent inactivated influenza vaccines for the at-risk population in Italy

Seasonal influenza is caused by two subtypes of influenza A and two lineages of influenza B. Although trivalent influenza vaccines (TIVs) contain both circulating A strains, they contain only a single B-lineage strain. This can lead to mismatches between the vaccine and predominant circulating B lineages, a concern especially for at-risk populations. Quadrivalent influenza vaccines (QIVs) containing a strain from both B lineages have been developed to improve protection against influenza. Here, we used a cost-utility model to examine whether switching from TIV to QIV would be cost-effective for the at-risk population in Italy. Costs were estimated from the payer and societal perspectives. The discount rate for outcomes was 3.0%. Univariate and probabilistic sensitivity analyses were performed to examine the effects of variations in parameters. Switching from TIV to QIV in Italy was estimated to increase quality-adjusted life-years (QALYs) and produce cost savings, including €1.6 million for hospitalization and approximately €2 million in productivity. The incremental cost-effectiveness ratio was €23,426 per QALY from a payer perspective and €21,096 per QALY from a societal perspective. Switching to QIV was most cost-effective for individuals ≥ 65 years of age (€19,170 per QALY). Probabilistic sensitivity analysis showed that the switching from TIV to QIV would be cost-effective for > 91% of simulation at a maximum willingness-to-pay threshold of €40,000 per QALY gained. Although the model did not take herd protection into account, it predicted that the switch from TIV to QIV would be cost-effective for the at-risk population in Italy.

FluHMM: A simple and flexible Bayesian algorithm for sentinel influenza surveillance and outbreak detection

Timely detection of the seasonal influenza epidemic is important for public health action. We introduce FluHMM, a simple but flexible Bayesian algorithm to detect and monitor the seasonal epidemic on sentinel surveillance data. No comparable historical data are required for its use. FluHMM segments a typical influenza surveillance season into five distinct phases with clear interpretation (pre-epidemic, epidemic growth, epidemic plateau, epidemic decline and post-epidemic) and provides the posterior probability of being at each phase for every week in the period under surveillance, given the available data. An alert can be raised when the probability that the epidemic has started exceeds a given threshold. An accompanying R package facilitates the application of this method in public health practice. We apply FluHMM on 12 seasons of sentinel surveillance data from Greece, and show that it achieves very good sensitivity, timeliness and perfect specificity, thereby demonstrating its usefulness. We further discuss advantages and limitations of the method, providing suggestions on how to apply it and highlighting potential future extensions such as with integrating multiple surveillance data streams.

Evolution of Therapeutic Antibodies, Influenza Virus Biology, Influenza, and Influenza Immunotherapy

This narrative review article summarizes past and current technologies for generating antibodies for passive immunization/immunotherapy. Contemporary DNA and protein technologies have facilitated the development of engineered therapeutic monoclonal antibodies in a variety of formats according to the required effector functions. Chimeric, humanized, and human monoclonal antibodies to antigenic/epitopic myriads with less immunogenicity than animal-derived antibodies in human recipients can be produced in vitro. Immunotherapy with ready-to-use antibodies has gained wide acceptance as a powerful treatment against both infectious and noninfectious diseases. Influenza, a highly contagious disease, precipitates annual epidemics and occasional pandemics, resulting in high health and economic burden worldwide. Currently available drugs are becoming less and less effective against this rapidly mutating virus. Alternative treatment strategies are needed, particularly for individuals at high risk for severe morbidity. In a setting where vaccines are not yet protective or available, human antibodies that are broadly effective against various influenza subtypes could be highly efficacious in lowering morbidity and mortality and controlling unprecedented epidemic/pandemic. Prototypes of human single-chain antibodies to several conserved proteins of influenza virus with no Fc portion (hence, no ADE effect in recipients) are available. These antibodies have high potential as a novel, safe, and effective anti-influenza agent.

The burden of influenza A and B in Mexico from the year 2010 to 2013: An observational, retrospective, database study, on records from the Directorate General of Epidemiology database

Despite vaccination programs, influenza still represents a significant disease burden in Mexico. We conducted an observational, retrospective analysis to better understand the epidemiological situation of the influenza virus in Mexico. Analysis of the seasonal patterns of influenza A and B were based on the Directorate General of Epidemiology dataset of influenza-like illness(ILI), and severe acute respiratory infection(SARI) that were recorded between January 2010 and December 2013. Our objectives were 1) to describe influenza A and B activity, by age group, and subtype and, 2) to analyze the number of laboratory-confirmed cases presenting with ILI by influenza type, the regional distribution of influenza, and its clinical features. Three periods of influenza activity were captured: August 2010-January 2011, December 2011-March 2012, and October 2012-March 2013. Cases were reported throughout Mexico, with 50.3% (n = 10,320) of cases found in 18-49 year olds. Over the entire capture period, a total of 76,085 ILI/SARI episodes had swab samples analyzed for influenza, 27% were positive. During the same period, influenza A cases were higher in the 18-49 years old, and influenza B cases in both 5-17 and 18-49 age groups. Peak activity occurred in January 2012 (n = 4,159) and December 2012 (n = 348) for influenza A and B respectively. This analysis confirms that influenza is an important respiratory pathogen for children and adults in Mexico despite vaccination recommendations. School-age children and adolescents were more prone to influenza B infection; while younger adults were susceptible to both influenza A and B viruses. Over the seasons, influenza A and B co-circulated.

Heterogeneous estimates of influenza virus types A and B in the elderly: Results of a meta-regression analysis

Influenza has many age‐dependent characteristics. A previous systematic review of randomized controlled trials showed that the detection rate of influenza B was higher in children than in non‐elderly adults. However, no comprehensive reviews have targeted the elderly, who carry the main burden of disease. We aimed to quantify the relative detection rates of virus types A and B among the elderly, to identify factors affecting these proportions, and to compare type distribution among seniors and younger age‐classes. A comprehensive literature search was conducted to identify multiseason studies reporting A and B virus type distributions in the elderly. A random‐effects meta‐analysis was planned to quantify the prevalence of type B among elderly subjects with laboratory‐confirmed influenza. Meta‐regression was then applied to explain the sources of heterogeneity. Across 27 estimates identified, the type B detection rate among seniors varied from 5% to 37%. Meta‐analysis was not feasible owing to high heterogeneity (I² = 98.5%). Meta‐regression analysis showed that study characteristics, such as number of seasons included, hemisphere, and setting, could have contributed to the heterogeneity observed. The final adjusted model showed that studies that included both outpatients and inpatients reported a significantly (P = .024) lower proportion than those involving outpatients only. The detection rate of type B among the elderly was generally lower than in children/adolescents, but not non‐elderly adults. Influenza virus type B has a relatively low detection rate in older adults, especially in settings covering both inpatients and outpatients. Public health implications are discussed.

Trends of influenza B during the 2010-2016 seasons in 2 regions of north and south Italy: The impact of the vaccine mismatch on influenza immunisation strategy

Influenza A and B viruses are responsible for respiratory infections, representing globally seasonal threats to human health. The 2 viral types often co-circulate and influenza B plays an important role in the spread of infection. A 6-year retrospective surveillance study was conducted between 2010 and 2016 in 2 large administrative regions of Italy, located in the north (Liguria) and in the south (Sicily) of the country, to describe the burden and epidemiology of both B/Victoria and B/Yamagata lineages in different healthcare settings. Influenza B viruses were detected in 5 of 6 seasonal outbreaks, exceeding influenza A during the season 2012-2013. Most of influenza B infections were found in children aged ≤ 14 y and significant differences were observed in the age-groups infected by the different lineages. B/Victoria strains prevailed in younger population than B/Yamagata, but also were more frequently found in the community setting. Conversely, B/Yamagata viruses were prevalent among hospitalized cases suggesting their potential role in the development of more severe disease. The relative proportions of viral lineages varied from year to year, resulting in different lineage-level mismatch for the B component of trivalent influenza vaccine. Our findings confirmed the need for continuous virological surveillance of seasonal epidemics and bring attention to the adoption of universal influenza immunization program in the childhood. The use of tetravalent vaccine formulations may be useful to improve the prevention and control of the influenza burden in general population.

Possible interference between seasonal epidemics of influenza and other respiratory viruses in Hong Kong, 2014-2017

Background

Unlike influenza viruses, little is known about the prevalence and seasonality of other respiratory viruses because laboratory surveillance for non-influenza respiratory viruses is not well developed or supported in China and other resource-limited countries. We studied the interference between seasonal epidemics of influenza viruses and five other common viruses that cause respiratory illnesses in Hong Kong from 2014 to 2017.

Methods

The weekly laboratory-confirmed positive rates of each virus were analyzed from 2014 to 2017 in Hong Kong to describe the epidemiological trends and interference between influenza viruses, respiratory syncytial virus (RSV), parainfluenza virus (PIV), adenovirus, enterovirus and rhinovirus. A sinusoidal model was established to estimate the peak timing of each virus by phase angle parameters.

Results

Seasonal features of the influenza viruses, PIV, enterovirus and adenovirus were obvious, whereas annual peaks of RSV and rhinovirus were not observed. The incidence of the influenza viruses usually peaked in February and July, and the summer peaks in July were generally caused by the H3 subtype of influenza A alone. When influenza viruses were active, other viruses tended to have a low level of activity. The peaks of the influenza viruses were not synchronized. An epidemic of rhinovirus tended to shift the subsequent epidemics of the other viruses.

Conclusion

The evidence from recent surveillance data in Hong Kong suggests that viral interference during the epidemics of influenza viruses and other common respiratory viruses might affect the timing and duration of subsequent epidemics of a certain or several viruses.

Estimating the burden of seasonal influenza in Spain from surveillance of mild and severe influenza disease, 2010-2016

Background

Estimating the national burden of influenza disease is challenging. We aimed to estimate the disease burden of seasonal influenza in Spain, at the primary care and hospital level, over the 6 influenza seasons after 2009 pandemic.

Methods

We used data from the Spanish Influenza Sentinel Surveillance System to estimate weekly influenza rates and the number of influenza‐like illness (ILI) and mild confirmed influenza cases (MCIC). From the surveillance of severe hospitalized confirmed influenza cases (SHCIC), we obtained hospitalization rates and total number of SHCIC, intensive care unit (ICU) admissions and deaths in influenza hospitalized patients. We estimated both mild and severe influenza cases, overall, and by age‐group (<5, 5‐14, 15‐64, and ≥65 years).

Results

The highest cumulative rates of MCIC were observed in <15 years (1395‐3155 cases/100 000 population in 5‐14 years) and the lowest in ≥65 years (141‐608 cases/100 000 population). SHCIC rates revealed a characteristic U‐shaped distribution, with annual average hospitalization rates of 16.5 and 18.9 SHCIC/100, 000 p in 0‐4 years, and ≥65 years, respectively. We estimated an annual average of 866 868 cases of ILI attended in primary care (55% were MCIC), 3616 SHCIC, 1232 ICU admissions, and 437 deaths in SHCIC. The percentage of ICU admission among SHCIC was highest at 15‐64 years (42%), while the hospitalization fatality rate ranged from 1% in 0‐4 years to 18% in ≥65 years.

Conclusions

The ongoing Spanish Influenza Surveillance System allowed obtaining crucial information regarding the impact of mild and severe influenza in Spain.

Quadrivalent inactivated influenza vaccine (VaxigripTetra™)

INTRODUCTION

VaxigripTetra™ (IIV4; Sanofi Pasteur) is a quadrivalent split-virion influenza vaccine approved in Europe in 2016 for individuals ≥ 3 years of age. IIV4 builds on the well-established record of the trivalent split-virion influenza vaccine (Vaxigrip®). Areas covered: This literature review summarizes the rationale for developing quadrivalent influenza vaccines and discusses the phase III clinical trial results supporting the immunogenicity, safety, and tolerability of IIV4. Expert commentary: IIV4 is immunogenic and well tolerated. Adding a second B strain to the trivalent split-virion influenza vaccine provides a superior immune response for the additional strain but does not reduce the immune response for the three other strains or negatively affect the safety profile. By offering broader protection against co-circulating influenza B lineages, IIV4 has the potential to further reduce influenza-related morbidity and mortality beyond that achieved with trivalent vaccines.

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.

Fifteen years of epidemiologic, virologic and syndromic influenza surveillance: A focus on type B virus and the effects of vaccine mismatch in Liguria region, Italy

In order to estimate the burden of influenza and to describe the genetic evolutionary pattern and antigenic variability of type B viral strains, data deriving from 3 surveillance systems active in Liguria region, Northern Italy, were described. Since the re-emergence of the Victoria lineage in 2001, the clinical-epidemiological and syndromic surveillances demonstrated the heavy burden of influenza like illness (ILI) syndrome. Focusing on type B influenza virus, it predominated or played a relevant epidemic role in the 50% of the evaluated influenza seasons. Furthermore, the virologic surveillance demonstrated the frequent co-circulation of both lineages an heterogeneous circulation of different influenza B strains, determining a partial or complete mismatch in at least 6 influenza seasons. The undemonstrated cross-reactivity between lineages and the unpredictability of predominant lineage arose the scientific debate about the opportunity to include the quadrivalent influenza vaccine among the preventive tools to improve the protection against type B viruses. The integration of different surveillance systems highly contribute to estimate the poorly evaluated burden of type B influenza virus and help to find variants to include in the vaccine formulation.

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.