Variation in Influenza B Virus Epidemiology by Lineage, China

Considerations when treating influenza infections with oseltamivir

INTRODUCTION

Since the coronavirus disease 2019-mandated social distancing policy has been lifted worldwide, the circulation of influenza is expected to resume. Currently, oseltamivir is approved as the first-line agent for influenza prevention and treatment.

AREAS COVERED

This paper reviews the updated evidence in the pharmacology, resistance mechanisms, clinical pharmacy management, and real-world data on oseltamivir for influenza.

EXPERT OPINION

Oseltamivir is an oral prodrug of oseltamivir carboxylate, an influenza A and B neuraminidase inhibitor. Recently, the therapeutic efficacy of oseltamivir has been demonstrated in several trials. Oseltamivir is generally well-tolerated but may lead to neuropsychiatric events and bleeding. Oseltamivir-resistant influenza virus has been associated with the H275Y mutation in the influenza A(H1N1)pdm09 virus, while most strains are still sensitive to oseltamivir. Dose adjustment for oseltamivir should be based on creatinine clearance and body weight in pediatric patients with renal failure. According to real-world data from Nanfang Hospital, the annual number of patients prescribed oseltamivir declined from 35,711 in 2019 to 8,971 in 2020, with marked increases in 2022 (20,213) and 2023 (18,071). Among the 206 inpatients, children aged < 6 years who were treated with oseltamivir had the shortest duration to defervescence.

Immune imprinting in early life shapes cross-reactivity to influenza B virus haemagglutinin

Influenza exposures early in life are believed to shape future susceptibility to influenza infections by imprinting immunological biases that affect cross-reactivity to future influenza viruses. However, direct serological evidence linked to susceptibility is limited. Here we analysed haemagglutination-inhibition titres in 1,451 cross-sectional samples collected between 1992 and 2020, from individuals born between 1917 and 2008, against influenza B virus (IBV) isolates from 1940 to 2021. We included testing of 'future' isolates that circulated after sample collection. We show that immunological biases are conferred by early life IBV infection and result in lineage-specific cross-reactivity of a birth cohort towards future IBV isolates. This translates into differential estimates of susceptibility between birth cohorts towards the B/Yamagata and B/Victoria lineages, predicting lineage-specific birth-cohort distributions of observed medically attended IBV infections. Our data suggest that immunological measurements of imprinting could be important in modelling and predicting virus epidemiology.

An exploration of the value of NLR, PLR, LMR, and WBC × CRP for the diagnosis and treatment of influenza B in adults

The aim of the study was to study the diagnostic and therapeutic utility of NLR (neutrophil-to-lymphocyte ratio), LWR (lymphocyte-to-monocyte ratio), PLR (platelet-to-lymphocyte ratio), and WBC × CRP (WBC: white cell count, CRP: C-reactive protein) in patients with influenza B. This retrospective study included 122 adult patients with influenza B, 176 adult patients with bacterial infection, and 119 adult healthy physical examinees for routine blood examination and CRP testing, calculation of NLR, LMR, PLR, and WBC × CRP for relevant statistical analysis, monitoring of NLR, LMR, PLR and WBC × CRP in patients with influenza B during relevant treatment. All indicators, except for WBC and NLR, had no statistical differences between the influenza B group, the normal control group, and the influenza B group and bacterial infection group, respectively, and showed no statistical significance for the differences between the groups. The diagnostic effect of LMR and WBC × CRP was deemed good or excellent in patients with influenza B, healthy people, and patients with a bacterial infection. Conversely, NLR and PLR could only distinguish patients with influenza B from healthy people but remained unable to identify different pathogens. Moreover, many false negatives were noted for WBC and CRP during the diagnosis of influenza B. Also, NLR, LMR, PLR, and WBC × CRP exerted a good effect in evaluating curative effect and conditions for influenza B. LMR and WBC × CRP have a relatively high value in the early diagnosis of adults suffering from influenza B. Also, NLR and PLR excelled at differentiating adult patients with influenza B from healthy people. Therefore, NLR, PLR, LMR, and WBC × CRP can all be used for disease course monitoring and efficacy evaluation.

Epidemiological features of seasonal influenza transmission among 11 climate zones in Chinese Mainland

BACKGROUND

Previous studies provided some evidence of meteorological factors influence seasonal influenza transmission patterns varying across regions and latitudes. However, research on seasonal influenza activities based on climate zones are still in lack. This study aims to utilize the ecological-based Köppen Geiger climate zones classification system to compare the spatial and temporal epidemiological characteristics of seasonal influenza in Chinese Mainland and assess the feasibility of developing an early warning system.

METHODS

Weekly influenza cases number from 2014 to 2019 at the county and city level were sourced from China National Notifiable Infectious Disease Report Information System. Epidemic temporal indices, time series seasonality decomposition, spatial modelling theories including Moran's I and local indicators of spatial association were applied to identify the spatial and temporal patterns of influenza transmission.

RESULTS

All climate zones had peaks in Winter-Spring season. Arid, desert, cold (BWk) showed up the first peak. Only Tropical, savannah (Aw) and Temperate, dry winter with hot summer (Cwa) zones had unique summer peak. Temperate, no dry season and hot summer (Cfa) zone had highest average incidence rate (IR) at 1.047/100,000. The Global Moran's I showed that average IR had significant clustered trend (z = 53.69, P < 0.001), with local Moran's I identified high-high cluster in Cfa and Cwa. IR differed among three age groups between climate zones (0-14 years old: F = 26.80, P < 0.001; 15-64 years old: F = 25.04, P < 0.001; Above 65 years old: F = 5.27, P < 0.001). Age group 0-14 years had highest average IR in Cwa and Cfa (IR = 6.23 and 6.21) with unique dual peaks in winter and spring season showed by seasonality decomposition.

CONCLUSIONS

Seasonal influenza exhibited distinct spatial and temporal patterns in different climate zones. Seasonal influenza primarily emerged in BWk, subsequently in Cfa and Cwa. Cfa, Cwa and BSk pose high risk for seasonal influenza epidemics. The research finds will provide scientific evidence for developing seasonal influenza early warning system based on climate zones.

Evaluating the effectiveness and cost-effectiveness of free influenza vaccination policy for older adults in Yinzhou, China: Study protocol of a real-world analyses

BACKGROUND

Influenza causes excessive morbidity and mortality among older adults. While influenza vaccine provides protection against its infection, the vaccination coverage in China among older adults has been very low. Previous evidence on the cost-effectiveness of government-sponsored free influenza vaccination programs in China was primarily based on literature data, which might not always reflect real-world patient populations. The Yinzhou Health Information System (YHIS) is a regional database that captures electronic health records, insurance claims data, etc. for all residents in Yinzhou district, Zhejiang province, China. We will use YHIS to study the effectiveness, influenza-related direct medical cost and cost-effectiveness analysis (CEA) of the free influenza vaccination program for older adults. In this paper, we describe the study design and innovations in detail.

METHODS

We will establish a retrospective cohort of permanent older residents aged 65 and over, using YHIS between 2016 and 2021. We will estimate the vaccine coverage rate, influenza incidence rate and influenza-related direct medical cost from 2016 to 2021. Regression discontinuity will be used to estimate vaccine effectiveness for the 2020/2021 season. We will build a decision tree model to compare the cost-effectiveness of three influenza vaccination options (free trivalent influenza vaccine, free quadrivalent influenza vaccine, and no policy) from both societal and health system perspectives. Parameter inputs will be gathered from both YHIS and published literature. We will calculate the incremental cost-effectiveness ratio with cost and quality-adjusted life years (QALYs) discounted at 5 % annually.

DISCUSSION

Our CEA solidifies multiple sources including regional real-world data and literature for a rigorous evaluation of the government-sponsored free influenza vaccination program. The results will provide real-world evidence from real-world data on the cost-effectiveness of a real-world policy. Our findings are expected to support evidence-based policy making and to promote health for older adults.

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Spatial timing of circulating seasonal influenza A and B viruses in China from 2014 to 2018

Major outbreaks of influenza virus occurred in China in 2017-2018. To describe the pattern of influenza circulation and timing of seasonal epidemics, we analyzed data from influenza-like illness (ILI) specimens on surveillance wards of sentinel hospitals during 2014-2018. Among 1,890,084 ILI cases, 324,211 (17.2%) tested positive for influenza. Influenza A virus (particularly A/H3N2), which circulates annually, was detected in 62% of cases, compared with influenza B virus in 38% of cases. The detection rate of A/H1N1, A/H3N2, B/Victoria, and B/Yamagata viruses were 3.56%, 7.07%, 2.08%, and 3.45%, respectively. Influenza prevalence was generally stable over the four years analyzed, but obvious outbreaks occurred in 2015-2016 (17.28%) and 2017-2018 (22.67%), with B/Victoria and B/Yamagata contributing to these outbreaks, respectively. In the south, a characteristic peak in infections was detected in the summer (week 23-38), which was not detected in the north. Influenza B was found high frequency in school-age children (5-14 years) with 4.78% of B/Victoria and 6.76% of B/Yamagata. Therefore, the epidemiological characteristics of seasonal influenza were complex in China during 2014-2018, presenting distinctions in region, season, and susceptible population. These findings underline the importance of enhancing year-round influenza surveillance and provide a reference for the timing and variety of influenza vaccination.

Epidemiological features and trends in the mortality rates of 10 notifiable respiratory infectious diseases in China from 2004 to 2020: Based on national surveillance

Objectives

The aim of this study is to describe, visualize, and compare the trends and epidemiological features of the mortality rates of 10 notifiable respiratory infectious diseases in China from 2004 to 2020.

Setting

Data were obtained from the database of the National Infectious Disease Surveillance System (NIDSS) and reports released by the National and local Health Commissions from 2004 to 2020. Spearman correlations and Joinpoint regression models were used to quantify the temporal trends of RIDs by calculating annual percentage changes (APCs) in the rates of mortality.

Results

The overall mortality rate of RIDs was stable across China from 2004 to 2020 (R = -0.38, P = 0.13), with an APC per year of -2.2% (95% CI: -4.6 to 0.3; P = 0.1000). However, the overall mortality rate of 10 RIDs in 2020 decreased by 31.80% (P = 0.006) compared to the previous 5 years before the COVID-19 pandemic. The highest mortality occurred in northwestern, western, and northern China. Tuberculosis was the leading cause of RID mortality, and mortality from tuberculosis was relatively stable throughout the 17 years (R = -0.36, P = 0.16), with an APC of -1.9% (95% CI -4.1 to 0.4, P = 0.1000). Seasonal influenza was the only disease for which mortality significantly increased (R = 0.73, P = 0.00089), with an APC of 29.70% (95% CI 16.60-44.40%; P = 0.0000). The highest yearly case fatality ratios (CFR) belong to avian influenza A H5N1 [687.5 per 1,000 (33/48)] and epidemic cerebrospinal meningitis [90.5748 per 1,000 (1,010/11,151)]. The age-specific CFR of 10 RIDs was highest among people over 85 years old [13.6551 per 1,000 (2,353/172,316)] and was lowest among children younger than 10 years, particularly in 5-year-old children [0.0552 per 1,000 (58/1,051,178)].

Conclusions

The mortality rates of 10 RIDs were relatively stable from 2004 to 2020 with significant differences among Chinese provinces and age groups. There was an increased mortality trend for seasonal influenza and concerted efforts are needed to reduce the mortality rate of seasonal influenza in the future.

Long term intrinsic cycling in human life course antibody responses to influenza A(H3N2): an observational and modeling study

Background

Over a life course, human adaptive immunity to antigenically mutable pathogens exhibits competitive and facilitative interactions. We hypothesize that such interactions may lead to cyclic dynamics in immune responses over a lifetime.

Methods

To investigate the cyclic behavior, we analyzed hemagglutination inhibition titers against 21 historical influenza A(H3N2) strains spanning 47 years from a cohort in Guangzhou, China, and applied Fourier spectrum analysis. To investigate possible biological mechanisms, we simulated individual antibody profiles encompassing known feedbacks and interactions due to generally recognized immunological mechanisms.

Results

We demonstrated a long-term periodicity (about 24 years) in individual antibody responses. The reported cycles were robust to analytic and sampling approaches. Simulations suggested that individual-level cross-reaction between antigenically similar strains likely explains the reported cycle. We showed that the reported cycles are predictable at both individual and birth cohort level and that cohorts show a diversity of phases of these cycles. Phase of cycle was associated with the risk of seroconversion to circulating strains, after accounting for age and pre-existing titers of the circulating strains.

Conclusions

Our findings reveal the existence of long-term periodicities in individual antibody responses to A(H3N2). We hypothesize that these cycles are driven by preexisting antibody responses blunting responses to antigenically similar pathogens (by preventing infection and/or robust antibody responses upon infection), leading to reductions in antigen-specific responses over time until individual's increasing risk leads to an infection with an antigenically distant enough virus to generate a robust immune response. These findings could help disentangle cohort effects from individual-level exposure histories, improve our understanding of observed heterogeneous antibody responses to immunizations, and inform targeted vaccine strategy.

Funding

This study was supported by grants from the NIH R56AG048075 (DATC, JL), NIH R01AI114703 (DATC, BY), the Wellcome Trust 200861/Z/16/Z (SR), and 200187/Z/15/Z (SR). This work was also supported by research grants from Guangdong Government HZQB-KCZYZ-2021014 and 2019B121205009 (YG and HZ). DATC, JMR and SR acknowledge support from the National Institutes of Health Fogarty Institute (R01TW0008246). JMR acknowledges support from the Medical Research Council (MR/S004793/1) and the Engineering and Physical Sciences Research Council (EP/N014499/1). The funders had no role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Estimating mortality associated with seasonal influenza among adults aged 65 years and above in China from 2011 to 2016: A systematic review and model analysis

BACKGROUND

Estimation of influenza disease burden is crucial for optimizing intervention strategies against seasonal influenza. This study aimed to estimate influenza-associated excess respiratory and circulatory (R&C) and all-cause (AC) mortality among older adults aged 65 years and above in mainland China from 2011 to 2016.

METHODS

Through a systematic review, we collected influenza-associated excess R&C and AC mortality data of older adults aged 65 years and above for specific cities/provinces in mainland China. Generalized linear models were fitted to estimate the corresponding excess mortality for older adults by province and nationwide, accounting for the potential variables of influenza virus activity, demography, economics, meteorology, and health service. All statistical analyses were conducted using R software.

RESULTS

A total of 9154 studies were identified in English and Chinese databases, and 11 (0.1%) were included in the quantitative synthesis after excluding duplicates and screening the title, abstract, and full text. Using a generalized linear model, the estimates of annual national average influenza-associated excess R&C and AC mortality among older adults aged 65 years and above were 111.8 (95% CI: 92.8-141.1) and 151.6 (95% CI: 127.6-179.3) per 100,000 persons, respectively. Large variations in influenza-associated excess R&C and AC mortality among older adults were observed among 30 provinces.

CONCLUSIONS

Influenza was associated with substantial excess R&C and AC mortality among older adults aged 65 years and above in China from 2011 to 2016. This analysis provides valuable evidence for the introduction of the influenza vaccine into the National Immunization Program for the elderly in China.

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

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

Genomic Epidemiology of Seasonal Influenza Circulation in China During Prolonged Border Closure from 2020 to 2021

China experienced a resurgence of seasonal influenza activity throughout 2021 despite intermittent control measures and prolonged international border closure. We show genomic evidence for multiple A(H3N2), A(H1N1), and B/Victoria transmission lineages circulating over 3 years, with the 2021 resurgence mainly driven by two B/Victoria clades. Phylodynamic analysis revealed unsampled ancestry prior to widespread outbreaks in December 2020, showing that influenza lineages can circulate cryptically under non-pharmaceutical interventions enacted against COVID-19. Novel haemagglutinin gene mutations and altered age profiles of infected individuals were observed, and Jiangxi province was identified as a major source for nationwide outbreaks. Following major holiday periods, fluctuations in the effective reproduction number were observed, underscoring the importance of influenza vaccination prior to holiday periods or travel. Extensive heterogeneity in seasonal influenza circulation patterns in China determined by historical strain circulation indicates that a better understanding of demographic patterns is needed for improving effective controls.

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

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

Global variation in early epidemic growth rates and reproduction number of seasonal influenza

INTRODUCTION

Little is known about global variation in early epidemic growth rates and effective reproduction numbers (R_e) of seasonal influenza. We aimed to estimate global variation in R_e of influenza type A and B during a single period.

METHODS

Country influenza detection time series from September 2017 through January 2019 were obtained from an international database. Type A and B epidemics by country were selected based on R_e estimates for a five-week moving window advanced by week. Associations of R_e with absolute latitude, Human Development Index, percent of the population aged <15 years and percent living rurally in each country were assessed.

RESULTS

Time series were included for 119 of 169 available countries. There were 100 countries with influenza A and 79 with B epidemics. Median R_e for both influenza A and B epidemics was 1.23 (ranges: A 1.10, 1.60; B 1.06, 1.58). R_e of influenza B, but not A, was independently associated with absolute latitude, increasing by 0.022 (95% CI 0.002, 0.043) per 10 degrees.

CONCLUSIONS

R_e of influenza A and B were similar. Only R_e of influenza B was associated with country characteristics; increasing with distance from the equator. The approach may be suitable for continuous R_e surveillance.

Homotypic protection against influenza in a pediatric cohort in Managua, Nicaragua

The period of protection from repeat infection following symptomatic influenza is not well established due to limited availability of longitudinal data. Using data from a pediatric cohort in Managua, Nicaragua, we examine the effects of natural influenza virus infection on subsequent infection with the same influenza virus subtype/lineage across multiple seasons, totaling 2,170 RT-PCR-confirmed symptomatic influenza infections. Logistic regression models assessed whether infection in the prior influenza season protected against homologous reinfection. We sequenced viruses from 2011-2019 identifying dominant clades and measuring antigenic distances between hemagglutinin clades. We observe homotypic protection from repeat infection in children infected with influenza A/H1N1pdm (OR 0.12, CI 0.02-0.88), A/H3N2 (OR 0.41, CI 0.24-0.73), and B/Victoria (OR 0.00, CI 0.00-0.14), but not with B/Yamagata viruses (OR 0.60, CI 0.09-2.10). Overall, protection wanes as time or antigenic distance increases. Individuals infected with one subtype or lineage of influenza virus have significantly lower odds of homologous reinfection for the following one to two years; after two years this protection wanes. This protection is demonstrated across multiple seasons, subtypes, and lineages among children.

Regional-based within-year seasonal variations in influenza-related health outcomes across mainland China: a systematic review and spatio-temporal analysis

BACKGROUND

China experiences large variations in influenza seasonal activity. We aim to update and improve the current understanding of regional-based within-year variations of influenza activity across mainland China to provide evidence for the planning and optimisation of healthcare strategies.

METHODS

We conducted a systematic review and spatio-temporal meta-analysis to assess regional-based within-year variations of ILI outpatient consultation rates, influenza test positivity rates amongst both ILI outpatients and SARI inpatients, and influenza-associated excess mortality rates. We searched English and Chinese databases for articles reporting time-series data on the four influenza-related outcomes at the sub-national and sub-annual level. After synthesising the data, we reported on the mean monthly rate, epidemic onset, duration, peak and intensity.

RESULTS

We included 247 (7.7%) eligible studies in the analysis. We found within-year influenza patterns to vary across mainland China in relation to latitude and geographic location. High-latitude provinces were characterised by having short and intense annual winter epidemics, whilst most mid-latitude and low-latitude provinces experience semi-annual epidemics or year-round activity. Subtype activity varied across the country, with A/H1N1pdm09 and influenza B occurring predominantly in the winter, whereas A/H3N2 activity exhibited a latitudinal divide with high-latitude regions experiencing a winter peak, whilst mid and low-latitude regions experienced a summer epidemic. Epidemic onsets and peaks also varied, occurring first in the north and later in the southeast. We found positive associations between all influenza health outcomes. In addition, seasonal patterns at the prefecture and county-level broadly resembled their wider province.

CONCLUSIONS

This is the first systematic review to simultaneously examine the seasonal variation of multiple influenza-related health outcomes at multiple spatial scales across mainland China. The seasonality information provided here has important implications for the planning and optimisation of immunisation programmes and healthcare provision, supporting the need for regional-based approaches to address variations in local epidemiology.

Influenza A and B outbreaks differed in their associations with climate conditions in Shenzhen, China

Under the variant climate conditions in the transitional regions between tropics and subtropics, the impacts of climate factors on influenza subtypes have rarely been evaluated. With the available influenza A (Flu-A) and influenza B (Flu-B) outbreak data in Shenzhen, China, which is an excellent example of a transitional marine climate, the associations of multiple climate variables with these outbreaks were explored in this study. Daily laboratory-confirmed influenza virus and climate data were collected from 2009 to 2015. Potential impacts of daily mean/maximum/minimum temperatures (T/T_max/T_min), relative humidity (RH), wind velocity (V), and diurnal temperature range (DTR) were analyzed using the distributed lag nonlinear model (DLNM) and generalized additive model (GAM). Under its local climate partitions, Flu-A mainly prevailed in summer months (May to June), and a second peak appeared in early winter (December to January). Flu-B outbreaks usually occurred in transitional seasons, especially in autumn. Although low temperature caused an instant increase in both Flu-A and Flu-B risks, its effect could persist for up to 10 days for Flu-B and peak at 17 C (relative risk (RR) = 14.16, 95% CI: 7.46-26.88). For both subtypes, moderate-high temperature (28 C) had a significant but delayed effect on influenza, especially for Flu-A (RR = 26.20, 95% CI: 13.22-51.20). The Flu-A virus was sensitive to RH higher than 76%, while higher Flu-B risks were observed at both low (< 65%) and high (> 83%) humidity. Flu-A was active for a short term after exposure to large DTR (e.g., DTR = 10 C, RR = 12.45, 95% CI: 6.50-23.87), whereas Flu-B mainly circulated under stable temperatures. Although the overall wind speed in Shenzhen was low, moderate wind (2-3 m/s) was found to favor the outbreaks of both subtypes. This study revealed the thresholds of various climatic variables promoting influenza outbreaks, as well as the distinctions between the flu subtypes. These data can be helpful in predicting seasonal influenza outbreaks and minimizing the impacts, based on integrated forecast systems coupled with short-term climate models.

Influenza-associated mortality in Australia, 2010 through 2019: High modelled estimates in 2017

INTRODUCTION

In Australia, the 2017 and 2019 influenza seasons were severe. High-dose or adjuvanted vaccines were introduced for ≥65 year-olds in 2018.

AIM

To compare influenza-associated mortality in 2017 and 2019 with the average for 2010-2019.

METHODS

We used time series modelling to obtain estimates of influenza-associated death rates for influenza A(H1N1)pdm09, A(H3N2) and B in Australia, in persons of all ages and <65, 65-74 and ≥75 years. Estimates were made for pneumonia and influenza (P&I, 2010-2018), respiratory (2010-2018), and all-cause outcomes (2010-2019).

RESULTS

During 2010 through 2018 (and 2019 for all-cause), influenza was estimated to be associated with an annual average of 2.1 (95% confidence interval (CI) 1.9, 2.4), 4.0 (95% CI 3.4, 4.6), and 11.6 (95% CI 8.4, 15.0) P&I, respiratory and all-cause deaths per 100,000 population, respectively. Influenza A(H1N1)pdm09 was estimated to be associated with less than one quarter of influenza-associated P&I and respiratory deaths, while A(H3N2) and B were each estimated to contribute approximately equally to the remaining influenza-associated deaths. In 2017, the respective rates were 7.8 (95% CI 7.1, 8.4), 12.3 (95% CI 10.9, 13.6) and 26.0 (95% CI 20.8, 32.0) per 100,000. In 2019, the all-cause estimate was 20.8 (95% CI 14.9, 26.7) per 100,000.

CONCLUSIONS

Seasonal influenza continues to be associated with substantial mortality in Australia, with at least double the average occurring in 2017. Age-specific monitoring of vaccine effectiveness is needed in Australia to understand higher mortality seasons.

A single N342D substitution in Influenza B Virus NA protein determines viral pathogenicity in mice

Influenza B virus (IBV) is one of the most important human respiratory viruses: it causes approximately one-third of the global influenza-related disease burden each year. However, compared with the several pathogenicity-related molecular markers that have been identified for influenza A virus (IAV), little is known about potential IBV pathogenicity-related markers. Here, although the IBV strain B/Anhui-Tunxi/1528/2014 (AH1528/14) exhibited a more efficient replication ability in vitro and higher pathogenicity in vivo compared with IBV strain B/Anhui-Baohe/127/2015 (AH127/15), only three amino acids differences (HA_A390E, NA_N342D and PB1_V212I) were observed among their full genomes. The contributions of each amino acid difference to the virus pathogenicity were further investigated. Compared with the wild type IBV virus rAH127, the recombinant virus harbouring a single substitution of HA_A390E had a similar phenotype, whereas the recombinant virus harbouring PB1_V212I replicated to a moderately higher titre in both MDCK cells and in mice. Notably, the virus harbouring NA_N342D showed significantly better growth properties in MDCK cells and higher fatality rates in mice. In addition, the presence of NA_N342D dramatically enhanced the viral neuraminidase activity. In conclusion, our study identified a novel IBV molecular marker, NA_N342D, that could significantly increase the virulence of IBV in mice.

The moving epidemic method applied to influenza surveillance in Guangdong, China

OBJECTIVES

The moving epidemic method (MEM) has been well used for assessing seasonal influenza epidemics in temperate regions. This study used the MEM to establish epidemic threshold for influenza in Guangdong, a subtropical province in China.

METHODS

Influenza virology surveillance data from 2011/2012 to 2017/2018 seasons in Guangdong were used with the MEM to calculate the epidemic thresholds and timeously detect the 2018/2019 influenza season epidemic. The weekly positive proportion of influenza A(H1N1)pdm09, A(H3N2), B/Victoria-lineage and B/Yamagata-lineage were separately adapted to calculate the subtype-specific epidemic thresholds. The performance of MEM was evaluated using a cross-validation procedure.

RESULTS

For the 2018/2019 influenza season, the epidemic threshold of a weekly positive proportion was 15.08%. Epidemic detection for the 2018/2019 season was 1 week in advance. Influenza A(H1N1)pdm09, B/Yamagata-lineage and B/Victoria-lineage prevailed during winter and spring and their epidemic thresholds were 5.12%, 4.53% and 4.38%, respectively. Influenza A(H3N2) was active in the summer, with an epidemic threshold of 11.99%.

CONCLUSIONS

Using influenza virology surveillance data stratified by types of influenza virus, the MEM was effectively used in Guangdong, China. This study provided a practical way for subtropical regions to establish local influenza epidemic thresholds.

Pathogenicity and transmissibility assessment of two strains of human influenza virus isolated in China in 2018

OBJECTIVE

Influenza season occurs every year in China, but its presentation was unusual in the period from December 2017 to early 2018. During this period, influenza activity was increasing across the country and was much greater than during the same period in previous years, with great harm to people's health.

METHODS

In this study, we isolated two human influenza virus strains-A/Hebei/F076/2018(H1N1) and B/Hebei/16275B/2018-from patients with severe influenza in Hebei, China, during the flu season in January 2018, and explored their genetic characteristics, pathogenicity, and transmissibility.

RESULTS

A/Hebei/F076/2018(H1N1) belongs to the human-like H1N1 influenza virus lineage, whereas B/Hebei/16275B/2018 belongs to the Victoria lineage and is closely related to the World Health Organization reference strain B/Brisbane/60/2008. Pathogenicity tests revealed that A/Hebei/F076/2018(H1N1) replicated much more strongly in mice, with mice exhibiting 40% mortality, whereas B/Hebei/16275B/2018 was not lethal. Both viruses could be transmitted through direct contact and by the aerosol route between guinea pigs, but the H1N1 strain exhibited higher airborne transmissibility.

CONCLUSIONS

These results may contribute to the monitoring of influenza mutation and the prevention of an influenza outbreak.

Variation by lineage in serum antibody responses to influenza B virus infections

Two lineages of influenza B virus currently co-circulate and have distinct antigenicity, termed Victoria and Yamagata after the B/Victoria/2/87 and B/Yamagata/16/88 strains, respectively. We analyzed antibody titer dynamics following PCR-confirmed influenza B virus infection in a longitudinal community-based cohort study conducted in Hong Kong from 2009–2014 to assess patterns in changes in antibody titers to B/Victoria and B/Yamagata viruses following infections with each lineage. Among 62 PCR-confirmed cases, almost half had undetectable hemagglutination inhibition (HAI) antibody titers to the lineage of infection both pre-infection and post-infection. Among those infected with influenza B/Victoria who showed an HAI titer response after infection, we found strong rises to the lineage of infection, positive but smaller cross-lineage HAI titer boosts, a small dependence of HAI titer boosts on pre-infection titers, and a shorter half-life of HAI titers in adults. Our study is limited by the low HAI sensitivity for non-ether-treated IBV antigen and the incapacity of performing other assays with higher sensitivity, as well as the mismatch between the B/Yamagata lineage circulating strain and the assay strain in one of the study seasons.

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.

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

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

Innate and adaptive immunity toward influenza B viruses

Despite annual vaccination, influenza B viruses (IBV) cause significant disease with substantial health and socio-economic impacts. Novel vaccination strategies inducing broadly protective and long-lasting immunity across IBV lineages are needed. However, as immune responses toward IBV are largely understudied, host–virus interactions and protective immune mechanisms need to be defined to rationally design such vaccines. Here, we summarize recent advances in our understanding of immunological mechanisms underpinning protection from IBV. We discuss how innate antiviral host factors inhibit IBV replication and the ways by which IBV escapes such restriction. We review the specificity of broadly cross-reactive antibodies and universal T cells, and the mechanisms by which they mediate protection. We highlight important knowledge gaps needing to be addressed to design improved IBV vaccines.

Epidemiological and evolutionary dynamics of influenza B virus in coastal Kenya as revealed by genomic analysis of strains sampled over a single season

The genomic epidemiology of influenza B virus (IBV) remains understudied in Africa despite significance to design of effective local and global control strategies. We undertook surveillance throughout 2016 in coastal Kenya, recruiting individuals presenting with acute respiratory illness at nine outpatient health facilities (any age) or admitted to the Kilifi County Hospital (<5 years old). Whole genomes were sequenced for a selected 111 positives; 94 (84.7%) of B/Victoria lineage and 17 (15.3%) of B/Yamagata lineage. Inter-lineage reassortment was detected in ten viruses; nine with B/Yamagata backbone but B/Victoria NA and NP segments and one with a B/Victoria backbone but B/Yamagata PB2, PB1, PA, and MP segments. Five phylogenomic clusters were identified among the sequenced viruses; (i), pure B/Victoria clade 1A (n = 93, 83.8%), (ii), reassortant B/Victoria clade 1A (n = 1, 0.9%), (iii), pure B/Yamagata clade 2 (n = 2, 1.8%), (iv), pure B/Yamagata clade 3 (n = 6, 5.4%), and (v), reassortant B/Yamagata clade 3 (n = 9, 8.1%). Using divergence dates and clustering patterns in the presence of global background sequences, we counted up to twenty-nine independent IBV strain introductions into the study area (∼900 km2) in 2016. Local viruses, including the reassortant B/Yamagata strains, clustered closely with viruses from neighbouring Tanzania and Uganda. Our study demonstrated that genomic analysis provides a clearer picture of locally circulating IBV diversity. The high number of IBV introductions highlights the challenge in controlling local influenza epidemics by targeted approaches, for example, sub-population vaccination or patient quarantine. The finding of divergent IBV strains co-circulating within a single season emphasises why broad immunity vaccines are the most ideal for influenza control in Kenya.

Characterization of Influenza A and B Viruses Circulating in Southern China During the 2017-2018 Season

The trivalent seasonal influenza vaccine was the only approved and available vaccine during the 2016–2018 influenza seasons. It did not include the B/Yamagata strain. In this study, we report an acute respiratory disease outbreak associated with influenza B/Yamagata infections in Guangzhou, Southern China (January through March, 2018). Among the 9914 patients, 2241 (22.6%) were positive for the influenza B virus, with only 312 (3.1%) positive for the influenza A virus. The influenza B/Yamagata lineage dominated during this period in Southern China. The highest incidence of influenza A virus infection occurred in the children aged 5–14 years. In contrast, populations across all age groups were susceptible to the influenza B virus. Phylogenetic, mutations, and 3D structure analyses of hemagglutinin (HA) genes were performed to assess the vaccine-virus relatedness. The recommended A/H1N1 vaccine strain (A/Michigan/45/2015) during both 2017–2018 and 2018–2019 was antigen-specific for these circulating isolates (clade 6B.1) in Spring 2018. An outbreak of influenza B/Yamagata (clade 3) infections in 2018 occurred during the absence of the corresponding vaccine during 2016–2018. The recommended influenza B/Yamagata vaccine strain (B/Phuket/3073/2013) for the following season (2018–2019) was antigen-specific. Although there were only a few influenza B/Victoria infections in Spring 2018, five amino acid mutations were identified in the HA antigenic sites of the 19 B/Victoria isolates (clade 1A), when compared with the 2016–2018 B/Victoria vaccine strain. The number was larger than expected and suggested that the influenza B HA gene may be more variable than previously thought. One of the mutations (K180N) was noted to likely alter the epitope and to potentially affect the viral antigenicity. Seven mutations were also identified in the HA antigenic sites of 2018–2020 B/Victoria vaccine strain, of which some or all may reduce immunogenicity and the protective efficacy of the vaccine, perhaps leading to more outbreaks in subsequent seasons. The combined epidemiological, phylogenetic, mutations, and 3D structural analyses of the HA genes of influenza strains reported here contribute to the understanding and evaluation of how HA mutations affect vaccine efficacy, as well as to providing important data for screening and selecting more specific, appropriate, and effective influenza vaccine candidate strains.

Characteristics of Seasonal Influenza Virus Activity in a Subtropical City in China, 2013-2019

BACKGROUND

To optimize seasonal influenza vaccination programs in regions with potentially complicated seasonal patterns, the epidemiological characteristics of seasonal influenza activity in a subtropical city of China were explored.

MATERIALS AND METHODS

Influenza virus data of patients with influenza-like illness (ILI) during 2013-2019 were collected from two sentinel hospitals in a subtropical region of China, Yichang city. The influenza virus positive rate among sampled ILI cases served as a proxy to estimate influenza seasonal characteristics, including periodicity, duration, peaks, and predominant subtypes/lineages. Epidemiological features of different years, seasons and age groups were analyzed, and vaccine mismatches were identified.

RESULTS

In total, 8693 ILI cases were included; 1439 (16.6%) were laboratory-confirmed influenza cases. The influenza A positive rate (10.6%) was higher than the influenza B positive rate (5.9%). There were three influenza circulation patterns in Yichang: (1) annual periodicity (in 2013-2014, 2015-2016 and 2018-2019), (2) semiannual periodicity (in 2014-2015), and (3) year-round periodicity (in 2016-2017 and 2017-2018). Summer epidemics existed in two of the six years and were dominated by influenza A/H3N2. Winter and spring epidemics occurred in five of the six years, and A/H1N1, A/H3N2, B/Victoria, and B/Yamagata were codominant. During the study period, the predominant lineages, B/Victoria in 2015-16 and B/Yamagata in 2017-2018, were both mismatched with the influenza B component of the trivalent vaccine. Children 5-14 years old (26.4%) and individuals over 60 years old (16.9%) had the highest influenza positive rates.

CONCLUSIONS

The seasonal epidemic period and the predominant subtype/lineage of influenza viruses in Yichang city are complex. Influenza vaccination timing and strategies need to be optimized according to the local features of influenza virus activity.

The complex associations of climate variability with seasonal influenza A and B virus transmission in subtropical Shanghai, China

Most previous studies focused on the association between climate variables and seasonal influenza activity in tropical or temperate zones, little is known about the associations in different influenza types in subtropical China. The study aimed to explore the associations of multiple climate variables with influenza A (Flu-A) and B virus (Flu-B) transmissions in Shanghai, China. Weekly influenza virus and climate data (mean temperature (MeanT), diurnal temperature range (DTR), relative humidity (RH) and wind velocity (Wv)) were collected between June 2012 and December 2018. Generalized linear models (GLMs), distributed lag non-linear models (DLNMs) and regression tree models were developed to assess such associations. MeanT exerted the peaking risk of Flu-A at 1.4 °C (2-weeks' cumulative relative risk (RR): 14.88, 95% confidence interval (CI): 8.67-23.31) and 25.8 °C (RR: 12.21, 95%CI: 6.64-19.83), Flu-B had the peak at 1.4 °C (RR: 26.44, 95%CI: 11.52-51.86). The highest RR of Flu-A was 23.05 (95%CI: 5.12-88.45) at DTR of 15.8 °C, that of Flu-B was 38.25 (95%CI: 15.82-87.61) at 3.2 °C. RH of 51.5% had the highest RR of Flu-A (9.98, 95%CI: 4.03-26.28) and Flu-B (4.63, 95%CI: 1.95-11.27). Wv of 3.5 m/s exerted the peaking RR of Flu-A (7.48, 95%CI: 2.73-30.04) and Flu-B (7.87, 95%CI: 5.53-11.91). DTR ≥ 12 °C and MeanT <22 °C were the key drivers for Flu-A and Flu-B, separately. The study found complex non-linear relationships between climate variability and different influenza types in Shanghai. We suggest the careful use of meteorological variables in influenza prediction in subtropical regions, considering such complex associations, which may facilitate government and health authorities to better minimize the impacts of seasonal influenza.

Spatiotemporal Analysis of Influenza in China, 2005-2018

Influenza is a major cause of morbidity and mortality worldwide, as well as in China. Knowledge of the spatial and temporal characteristics of influenza is important in evaluating and developing disease control programs. This study aims to describe an accurate spatiotemporal pattern of influenza at the prefecture level and explore the risk factors associated with influenza incidence risk in mainland China from 2005 to 2018. The incidence data of influenza were obtained from the Chinese Notifiable Infectious Disease Reporting System (CNIDRS). The Besag York Mollié (BYM) model was extended to include temporal and space-time interaction terms. The parameters for this extended Bayesian spatiotemporal model were estimated through integrated nested Laplace approximations (INLA) using the package R-INLA in R. A total of 702,226 influenza cases were reported in mainland China in CNIDRS from 2005–2018. The yearly reported incidence rate of influenza increased 15.6 times over the study period, from 3.51 in 2005 to 55.09 in 2008 per 100,000 populations. The temporal term in the spatiotemporal model showed that much of the increase occurred during the last 3 years of the study period. The risk factor analysis showed that the decreased number of influenza vaccines for sale, the new update of the influenza surveillance protocol, the increase in the rate of influenza A (H1N1)pdm09 among all processed specimens from influenza-like illness (ILI) patients, and the increase in the latitude and longitude of geographic location were associated with an increase in the influenza incidence risk. After the adjusting for fixed covariate effects and time random effects, the map of the spatial structured term shows that high-risk areas clustered in the central part of China and the lowest-risk areas in the east and west. Large space-time variations in influenza have been found since 2009. In conclusion, an increasing trend of influenza was observed from 2005 to 2018. The insufficient flu vaccine supplements, the newly emerging influenza A (H1N1)pdm09 and expansion of influenza surveillance efforts might be the major causes of the dramatic changes in outbreak and spatio-temporal epidemic patterns. Clusters of prefectures with high relative risks of influenza were identified in the central part of China. Future research with more risk factors at both national and local levels is necessary to explain the changing spatiotemporal patterns of influenza in China.

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.

Development and evaluation of a conventional RT-PCR for differentiating emerging influenza B/Victoria lineage viruses with hemagglutinin amino acid deletion from B/Yamagata lineage viruses

BACKGROUND

Recent influenza B/Victoria lineage viruses contain amino acid deletions at positions 162 to 164 of the haemagglutinin (HA) protein. These amino acid deletions have affected the detection of B/Victoria lineage viruses by the lineage-specific conventional reverse-transcription polymerase chain reaction (RT-PCR) that was recommended by World Health Organization (WHO).

OBJECTIVES

We aimed to develop and evaluate a novel lineage-specific RT-PCR for rapid differentiation of the contemporary B/Victoria lineage from B/Yamagata lineage viruses.

STUDY DESIGN

Primers of our in-house RT-PCR were designed to avoid amino acid positions 162 to 164 and to target conserved regions of the HA gene that are specific for B/Victoria and B/Yamagata lineage viruses. Our in-house RT-PCR and WHO RT-PCR were evaluated using influenza B positive clinical specimens or virus culture isolates. Influenza B virus lineage was confirmed by Sanger sequencing.

RESULTS

A total of 105 clinical specimens or virus culture isolates were retrieved, including 83 with B/Victoria lineage and 22 with B/Yamagata lineage viruses. Our in-house RT-PCR correctly identified B/Victoria lineage viruses in all 83 samples, including 82 samples with double or triple amino acid deletion in the HA protein. Conversely, the WHO lineage-specific conventional RT-PCR failed to detect any of the 82 samples with HA amino acid deletions. For the 22 samples with B/Yamagata lineage viruses, both RT-PCR assays have correctly identified B/Yamagata lineage in all samples.

CONCLUSIONS

Our novel lineage-specific RT-PCR has successfully detected all contemporary B/Victoria lineage viruses with amino acid deletions in HA. This protocol is especially useful for laboratories without the equipment for real-time PCR.

Spatial, Temporal and Genetic Dynamics Characteristics of Influenza B Viruses in China, 1973-2018

Annual influenza B virus epidemics and outbreaks cause severe influenza diseases in humans and pose a threat to public health. China is an important epidemic area of influenza B viruses. However, the spatial, temporal transmission pathways and the demography history of influenza B viruses in China remain unknown. We collected the haemagglutinin gene sequences sampled of influenza B virus in China between 1973 and 2018. A Bayesian Markov chain Monte Carlo phylogeographic discrete approach was used to infer the spatial and temporal phylodynamics of influenza B virus. The Bayesian phylogeographic analysis of influenza B viruses showed that the North subtropical and South subtropical zones are the origins of the Victoria and Yamagata lineage viruses, respectively. Furthermore, the South temperate and North subtropical zones acted as transition nodes in the Victoria lineage virus dispersion network and that the North subtropical and Mid subtropical zones acted as transition nodes in the Yamagata lineage virus dispersion network. Our findings contribute to the knowledge regarding the spatial and temporal patterns of influenza B virus outbreaks in China.

Naproxen Exhibits Broad Anti-influenza Virus Activity in Mice by Impeding Viral Nucleoprotein Nuclear Export

Naproxen is a non-steroidal anti-inflammatory drug that has previously been shown to exert antiviral activity against influenza A virus by inhibiting nucleoprotein (NP) binding to RNA. Here, we show that naproxen is a potential broad, multi-mechanistic anti-influenza virus therapeutic, as it inhibits influenza B virus replication both in vivo and in vitro. The anti-influenza B virus activity of naproxen is more efficient than that of the commonly used neuraminidase inhibitor oseltamivir in mice. Furthermore, the NP of influenza B virus (BNP) has a higher binding affinity to naproxen than influenza A virus NP (ANP). Specifically, naproxen targets the NP at residues F209 (BNP) and Y148 (ANP). This interaction antagonizes the nuclear export of NP normally mediated by the host export protein CRM1. This study reveals a crucial mechanism of broad-spectrum anti-influenza virus activity of naproxen, suggesting that the existing drug naproxen may be used as an anti-influenza drug.

Detection and characterization of type B influenza virus from influenza-like illness cases during the 2017-2018 winter influenza season in Beijing, China

In the winter of 2017-2018, there was significant influenza activity in China, resulting in unprecedented usage of influenza rapid antigen tests (IRAT) and neuraminidase inhibitors (NAIs). The aim of this study was to characterize the most prevalent influenza virus type in a clinical setting with respect to diagnosis and concomitant NAI treatment. From Dec 2017 to Jan 2018, 3257 patients with influenza-like illness (ILI) were screened using IRAT. We summarized and compared the results with the last influenza season. Subtyping of influenza B viruses and identification of NAI drug resistance mutations were carried out by sequencing the HA and NA genes and aligning these with genetic isotypes. The performance of IRAT and RT-PCR was compared. Screening results indicated that influenza B virus was the leading cause of this influenza epidemic, with children being more susceptible to infection than adults. Phylogenetic analysis revealed that the prevailing influenza B virus belonged to the Yamagata lineage and were genetically similar to strains isolated from North America in the same influenza season. Cross-continental spread of influenza/B/Yamagata occurred. NAI resistance mutations were not identified in the 18 samples analyzed. The current antiviral protocol was still effective for influenza B control. RT-PCR positivity was significantly higher than that of IRAT (P = 0.004). IRAT and RT-PCR had a consistency rate of 86.9%, with the consistency rates of the positive and negative cases being 54.3% and 97.3%, respectively. Clinicians should be alert to the possibility of obtaining false negative results when using IRAT, and RT-PCR is recommended to improve the accuracy of pathogen detection.

Understanding the complex seasonality of seasonal influenza A and B virus transmission: Evidence from six years of surveillance data in Shanghai, China

OBJECTIVES

Understanding the complexity of influenza subtype seasonality is critical to promoting a suitable vaccination program. The aim of this study was to identify and compare the seasonality and epidemiological features of seasonal influenza subtypes after the 2009 A/H1N1 pandemic and to lay a foundation for further investigation into the social and environmental factors affecting seasonal influenza virus transmission.

METHODS

Influenza-like illness (ILI) case surveillance was conducted in two sentinel hospitals in Pudong New Area, Shanghai between 2012 and 2018. Weekly data on ILI cases were analyzed. A time-series seasonal decomposition analysis was used to reveal the seasonality of influenza and epidemiological features among different subtypes.

RESULTS

In total, 10977 ILI patients were enrolled of whom 2385 (21.7%) had laboratory-confirmed influenza. Compared to influenza A (16.3%), influenza B (5.4%) was less frequently detected among the ILI patients (p<0.001). Semiannual epidemic peaks were identified in four of the years during the 6-year study period, while only one annual epidemic peak was found in the other two years. An epidemic peak occurred in each winter season, and a secondary peak also occasionally occurred in summer or spring. A/H3N2 predominated in both summer and winter, while A/H1N1, B/Yamagata, and B/Victoria circulated almost exclusively in winter or spring. Two lineages of influenza B seemed to predominate in alternating years.

CONCLUSIONS

This study highlights the complexity of seasonal influenza virus activity in a subtropical region of China, presenting both semiannual and annual epidemic peaks in different years. The results of this study may provide further insight into possible improvements in the timing of influenza vaccination in Shanghai, China.

Predominance of influenza B/Yamagata lineage viruses in Bulgaria during the 2017/2018 season

In this study, we investigated the antigenic and genetic characteristics of influenza viruses circulating in Bulgaria during the 2017/2018 season. The detection and typing/subtyping of influenza viruses were performed using real-time RT-PCR. Results of antigenic characterisation, phylogenetic and amino acid sequence analyses of representative influenza strains are presented. The season was characterised by the predominance of B/Yamagata viruses, accounting for 77% of detected influenza viruses, followed by A(H1N1)pdm09 (17%), B/Victoria (3.7%) and A(H3N2) (2.4%). The sequenced B/Yamagata, B/Victoria, A(H1N1)pdm09 and A(H3N2) viruses belonged to the genetic groups 3, 1A, 6B.1 and 3C.2a1, respectively. Amino acid analysis of B/Yamagata isolates revealed the presence of three changes in haemagglutinin (HA), eight changes in neuraminidase (NA) and a number of substitutions in internal proteins compared with the B/Phucket/3073/2013 vaccine virus. Despite the amino acid changes, B/Yamagata viruses remained antigenically related to the vaccine strain. B/Victoria isolates fell into a group of viruses with double deletion (Δ162-163) in HA1. Substitutions in HA and NA sequences of B/Victoria, A(H1N1)pdm09 and A(H3N2) viruses were also identified compared with the vaccine strains, including in antigenic sites. The results of this study confirm the genetic variability of circulating influenza viruses and the need for continual antigenic and molecular surveillance.

Prevalence of Common Respiratory Viral Infections and Identification of Adenovirus in Hospitalized Adults in Harbin, China 2014 to 2017

Background: Respiratory infections pose a great challenge in global health, and the prevalence of viral infection in adult patients has been poorly understood in northeast China. Harbin is one of the major cities in northeast China, and more than half of any given year in Harbin is occupied by winter. To reveal the viral etiology and seasonality in adult patients from Harbin, a 4-year consecutive survey was conducted in Harbin, China.

Methods: From January 2014 to December 2017, specimens were obtained from adult patients admitted to the Second Affiliated Hospital of Harbin Medical University with lower respiratory tract infections. Sputum samples were examined by direct immunofluorescence assays to detect seven common respiratory viruses, including influenza virus (type A and B), parainfluenza virus (type 1 to 3), respiratory syncytial virus and adenovirus. Adenovirus positive samples were seeded onto A549 cells to isolate viral strains. Phylogenetic analysis was conducted on the highly variable region of adenoviral hexon gene.

Results: A total of 1,300 hospitalized adult patients with lower respiratory tract infections were enrolled, in which 189 patients (14.5%) were detected as having at least one viral infection. The co-infection rate in this study was 25.9% (49/189). The dominant viral pathogen from 2014 to 2017 was parainfluenza virus, with a detection rate of 7.2%, followed by influenza virus, respiratory syncytial virus and adenovirus. Based on the climate seasons determined by daily average temperature, the highest overall viral detection rate was detected in spring (22.0%, 52/236), followed by winter (13.4%, 109/813), autumn (11.4%, 13/114) and summer (10.9%, 15/137). Adenovirus type 3 strains with slight variations were isolated from positive cases, which were closely related to the GB strain from the United States, as well as the Harbin04B strain isolated locally.

Conclusion: This study demonstrated that common respiratory viruses were partially responsible for hospitalized lower respiratory tract infections in adult patients from Harbin, China, with parainfluenza virus as the dominant viral pathogen. Climate seasons could be rational indicators for the seasonality analysis of airborne viral infections. Future surveillance on viral mutations would be necessary to reveal the evolutionary history of respiratory viruses.