Heterogeneity in Estimates of the Impact of Influenza on Population Mortality: A Systematic Review

Influenza-Associated Excess Mortality and Hospitalization in Germany from 1996 to 2018

INTRODUCTION

Influenza-associated excess mortality and morbidity is commonly estimated using statistical methods. In Germany, the Robert Koch Institute (RKI) uses the relative mortality distribution method (RMDM) to estimate influenza-associated excess mortality without reporting age-specific values. In order to better differentiate the distribution of the disease burden, a distinction by age is of high relevance. Therefore, we aimed to revise the existing excess mortality model and provide age-specific excess mortality estimates over multiple seasons. We also used the model to determine influenza-associated excess hospitalizations, since the RKI excess hospitalization model is currently based on another approach (i.e., combination of excess physician visits and hospitalized proportion).

METHODS

This study was a retrospective data analysis based on secondary data of the German population from 1996-2018. We adapted the RKI's method of estimating influenza-associated excess mortality with the RMDM and also applied this approach to excess hospitalizations. We calculated the number of excess deaths/hospitalizations using weekly and age-specific data.

RESULTS

Data available in Germany are suitable for addressing the restrictions of the RKI's mortality model. In total, we estimated 175,858 (176,482 with age stratification) influenza-associated excess all cause deaths between 1995-1996 and 2017-2018 ranging from 0 (17 with age stratification) in 2005-2006 to 25,599 (25,527 with age stratification) in 2017-2018. Total influenza-associated excess deaths were comparable to RKI's estimates in most seasons. Most excess deaths/hospitalizations occurred in patients aged ≥ 60 years (95.42%/57.49%) followed by those aged 35-59 years (3,80%/24,98%). Compared with our model, the RKI hospitalization model implies a substantial underestimation of excess hospitalizations (828,090 vs. 374,200 over all seasons).

CONCLUSION

This is the first study that provides age-specific estimates of influenza-associated excess mortality in Germany. The results clearly show that the main burden of influenza is in the elderly, for whom prevention and control measures should be prioritized.

Opportunities and challenges for T cell-based influenza vaccines

Vaccination remains our main defence against influenza, which causes substantial annual mortality and poses a serious pandemic threat. Influenza virus evades immunity by rapidly changing its surface antigens but, even when the vaccine is well matched to the current circulating virus strains, influenza vaccines are not as effective as many other vaccines. Influenza vaccine development has traditionally focused on the induction of protective antibodies, but there is mounting evidence that T cell responses are also protective against influenza. Thus, future vaccines designed to promote both broad T cell effector functions and antibodies may provide enhanced protection. As we discuss, such vaccines present several challenges that require new strategic and economic considerations. Vaccine-induced T cells relevant to protection may reside in the lungs or lymphoid tissues, requiring more invasive assays to assess the immunogenicity of vaccine candidates. T cell functions may contain and resolve infection rather than completely prevent infection and early illness, requiring vaccine effectiveness to be assessed based on the prevention of severe disease and death rather than symptomatic infection. It can be complex and costly to measure T cell responses and infrequent clinical outcomes, and thus innovations in clinical trial design are needed for economic reasons. Nevertheless, the goal of more effective influenza vaccines justifies renewed and intensive efforts.

Sequence-based detection of emerging antigenically novel influenza A viruses

The detection of evolutionary transitions in influenza A (H3N2) viruses' antigenicity is a major obstacle to effective vaccine design and development. In this study, we describe Novel Influenza Virus A Detector (NIAViD), an unsupervised machine learning tool, adept at identifying these transitions, using the HA1 sequence and associated physico-chemical properties. NIAViD performed with 88.9% (95% CI, 56.5-98.0%) and 72.7% (95% CI, 43.4-90.3%) sensitivity in training and validation, respectively, outperforming the uncalibrated null model-33.3% (95% CI, 12.1-64.6%) and does not require potentially biased, time-consuming and costly laboratory assays. The pivotal role of the Boman's index, indicative of the virus's cell surface binding potential, is underscored, enhancing the precision of detecting antigenic transitions. NIAViD's efficacy is not only in identifying influenza isolates that belong to novel antigenic clusters, but also in pinpointing potential sites driving significant antigenic changes, without the reliance on explicit modelling of haemagglutinin inhibition titres. We believe this approach holds promise to augment existing surveillance networks, offering timely insights for the development of updated, effective influenza vaccines. Consequently, NIAViD, in conjunction with other resources, could be used to support surveillance efforts and inform the development of updated influenza vaccines.

Resurgence of seasonal influenza driven by A/H3N2 and B/Victoria in succession during the 2023-2024 season in Beijing showing increased population susceptibility

During the COVID-19 pandemic, non-pharmaceutical interventions were introduced to reduce exposure to respiratory viruses. However, these measures may have led to an "immunity debt" that could make the population more vulnerable. The goal of this study was to examine the transmission dynamics of seasonal influenza in the years 2023-2024. Respiratory samples from patients with influenza-like illness were collected and tested for influenza A and B viruses. The electronic medical records of index cases from October 2023 to March 2024 were analyzed to determine their clinical and epidemiological characteristics. A total of 48984 positive cases were detected, with a pooled prevalence of 46.9% (95% CI 46.3-47.5). This season saw bimodal peaks of influenza activity, with influenza A peaked in week 48, 2023, and influenza B peaked in week 1, 2024. The pooled positive rates were 28.6% (95% CI 55.4-59.6) and 18.3% (95% CI 18.0-18.7) for influenza A and B viruses, respectively. The median values of instantaneous reproduction number were 5.5 (IQR 3.0-6.7) and 4.6 (IQR 2.4-5.5), respectively. The hospitalization rate for influenza A virus (2.2%, 95% CI 2.0-2.5) was significantly higher than that of influenza B virus (1.1%, 95% CI 0.9-1.4). Among the 17 clinical symptoms studied, odds ratios of 15 symptoms were below 1 when comparing influenza A and B positive inpatients, with headache, weakness, and myalgia showing significant differences. This study provides an overview of influenza dynamics and clinical symptoms, highlighting the importance for individuals to receive an annual influenza vaccine.

From respiratory diseases to nervous system disorders: Unraveling the certified causes of influenza-associated deaths in Poland from 2000 to 2019

Background

This study aims to accurately estimate influenza-associated deaths in Poland and their certified cause of death, due to significant discrepancies between official numbers and expected impact.

Methods

Excess influenza-associated mortality in Poland from 2000 to 2019 was calculated using Seasonal-Trend Decomposition Procedure based on LOESS (STL), which can detect non-linear trends and non-sinusoidal cycles. Excess mortality was then used as an explanatory variable in a model predicting monthly fluctuations of officially recorded causes of death from 2010 to 2019.

Results

A total of 142,000 conservative estimates of influenza-associated deaths were identified, representing 1.86% of overall mortality. Only 0.61% of influenza-associated deaths were officially recorded as influenza. Nearly half of certified influenza deaths were attributed to the seasonal baseline mortality, potentially doubling estimated impact based solely on influenza peaks. Influenza-associated deaths were frequently recorded as respiratory diseases (24.36%), with majority attributed to underlying conditions such as cardiovascular diseases (45.31%), cancer (9.06%), or diabetes (2.66%). Influenza-associated deaths were more commonly certified as nervous system diseases (1.84%) or mental disorders (1.04%), rather than influenza itself. There was a noticeable impact of influenza on secondary infections, such as meningococcal and gastrointestinal infections.

Conclusion

These findings highlight the importance of improved estimation for informing public health policy decisions.

COVID-19 mortality attenuated during widespread Omicron transmission, Denmark, 2020 to 2022

BackgroundIt sparked considerable attention from international media when Denmark lifted restrictions against COVID-19 in February 2022 amidst widespread transmission of the new SARS-CoV-2 Omicron variant and a steep rise in reported COVID-19 mortality based on the 30-day COVID-19 death count.AimOur aim was to investigate how coincidental infections affected COVID-19 mortality estimates following the introduction of the Omicron variant in late 2021.MethodsWe compared the 30-day COVID-19 death count with the observed mortality using three alternative mortality estimation methods; (i) a mathematical model to correct the 30-day COVID-19 death count for coincidental deaths, (ii) the Causes of Death Registry (CDR) and (iii) all-cause excess mortality.ResultsThere was a substantial peak in the 30-day COVID-19 death count following the emergence of the Omicron variant in late 2021. However, there was also a substantial change in the proportion of coincidental deaths, increasing from 10-20% to around 40% of the recorded COVID-19 deaths. The high number of 30-day COVID-19 deaths was not reflected in the number of COVID-19 deaths in the CDR and the all-cause excess mortality surveillance.ConclusionOur analysis showed a distinct change in the mortality pattern following the introduction of Omicron in late 2021 with a markedly higher proportion of people estimated to have died with, rather than of, COVID-19 compared with mortality patterns observed earlier in the COVID-19 pandemic. Our findings highlight the importance of incorporating alternative mortality surveillance methods to more correctly estimate the burden of COVID-19 as the pandemic continues to evolve.

Influenza-Associated Excess Mortality by Age, Sex, and Subtype/Lineage: Population-Based Time-Series Study With a Distributed-Lag Nonlinear Model

BACKGROUND

Accurate estimation of the influenza death burden is of great significance for influenza prevention and control. However, few studies have considered the short-term harvesting effects of influenza on mortality when estimating influenza-associated excess deaths by cause of death, age, sex, and subtype/lineage.

OBJECTIVE

This study aimed to estimate the cause-, age-, and sex-specific excess mortality associated with influenza and its subtypes and lineages in Guangzhou from 2015 to 2018.

METHODS

Distributed-lag nonlinear models were fitted to estimate the excess mortality related to influenza subtypes or lineages for different causes of death, age groups, and sex based on daily time-series data for mortality, influenza, and meteorological factors.

RESULTS

A total of 199,777 death certificates were included in the study. The average annual influenza-associated excess mortality rate (EMR) was 25.06 (95% empirical CI [eCI] 19.85-30.16) per 100,000 persons; 7142 of 8791 (81.2%) deaths were due to respiratory or cardiovascular mortality (EMR 20.36, 95% eCI 16.75-23.74). Excess respiratory and cardiovascular deaths in people aged 60 to 79 years and those aged ≥80 years accounted for 32.9% (2346/7142) and 63.7% (4549/7142) of deaths, respectively. The male to female ratio (MFR) of excess death from respiratory diseases was 1.34 (95% CI 1.17-1.54), while the MFR for excess death from cardiovascular disease was 0.72 (95% CI 0.63-0.82). The average annual excess respiratory and cardiovascular mortality rates attributed to influenza A (H3N2), B/Yamagata, B/Victoria, and A (H1N1) were 8.47 (95% eCI 6.60-10.30), 5.81 (95% eCI 3.35-8.25), 3.68 (95% eCI 0.81-6.49), and 2.83 (95% eCI -1.26 to 6.71), respectively. Among these influenza subtypes/lineages, A (H3N2) had the highest excess respiratory and cardiovascular mortality rates for people aged 60 to 79 years (20.22, 95% eCI 14.56-25.63) and ≥80 years (180.15, 95% eCI 130.75-227.38), while younger people were more affected by A (H1N1), with an EMR of 1.29 (95% eCI 0.07-2.32). The mortality displacement of influenza A (H1N1), A (H3N2), and B/Yamagata was 2 to 5 days, but 5 to 13 days for B/Victoria.

CONCLUSIONS

Influenza was associated with substantial mortality in Guangzhou, occurring predominantly in the elderly, even after considering mortality displacement. The mortality burden of influenza B, particularly B/Yamagata, cannot be ignored. Contrasting sex differences were found in influenza-associated excess mortality from respiratory diseases and from cardiovascular diseases; the underlying mechanisms need to be investigated in future studies. Our findings can help us better understand the magnitude and time-course of the effect of influenza on mortality and inform targeted interventions for mitigating the influenza mortality burden, such as immunizations with quadrivalent vaccines (especially for older people), behavioral campaigns, and treatment strategies.

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.

Systematic Review on the Cost-Effectiveness of Seasonal Influenza Vaccines in Older Adults

OBJECTIVES

Older adults are at high risk of influenza-related complications or hospitalization. The purpose of this systematic review is to assess the relative cost-effectiveness of all influenza vaccine options for older adults.

METHODS

This systematic review identified economic evaluation studies assessing the cost-effectiveness of influenza vaccines in adults ≥65 years of age from 5 literature databases. Two reviewers independently selected, extracted, and appraised relevant studies using the JBI Critical Appraisal Checklist for Economic Evaluations and Heyland's generalizability checklist. Costs were converted to 2019 Canadian dollars and adjusted for inflation and purchasing power parity.

RESULTS

A total of 27 studies were included. There were 18 comparisons of quadrivalent inactivated vaccine (QIV) versus trivalent inactivated vaccine (TIV): 5 showed QIV dominated TIV (ie, lower costs and higher health benefit), and 13 showed the results depended on willingness to pay (WTP). There were 9 comparisons of high-dose TIV (TIV-HD) versus TIV: 5 showed TIV-HD dominated TIV, and 4 showed the results depended on WTP. There were 8 comparisons of adjuvanted TIV (TIV-ADJ) versus TIV: 4 showed TIV-ADJ dominated TIV, and 4 showed the results depended on WTP. There were few pairwise comparisons among QIV, TIV-HD, and TIV-ADJ.

CONCLUSIONS

The evidence suggests QIV, TIV-HD, and TIV-ADJ are cost-effective against TIV for a WTP threshold of $50 000 per quality-adjusted life-year. Future studies should include new and existing vaccine options for broad age ranges and use more robust methodologies-such as real-world evaluations or modeling studies accounting for methodological, structural, and parameter uncertainty.

Prediction of Influenza Complications: Development and Validation of a Machine Learning Prediction Model to Improve and Expand the Identification of Vaccine-Hesitant Patients at Risk of Severe Influenza Complications

Influenza vaccinations are recommended for high-risk individuals, but few population-based strategies exist to identify individual risks. Patient-level data from unvaccinated individuals, stratified into retrospective cases (n = 111,022) and controls (n = 2,207,714), informed a machine learning model designed to create an influenza risk score; the model was called the Geisinger Flu-Complications Flag (GFlu-CxFlag). The flag was created and validated on a cohort of 604,389 unique individuals. Risk scores were generated for influenza cases; the complication rate for individuals without influenza was estimated to adjust for unrelated complications. Shapley values were used to examine the model’s correctness and demonstrate its dependence on different features. Bias was assessed for race and sex. Inverse propensity weighting was used in the derivation stage to correct for biases. The GFlu-CxFlag model was compared to the pre-existing Medial EarlySign Flu Algomarker and existing risk guidelines that describe high-risk patients who would benefit from influenza vaccination. The GFlu-CxFlag outperformed other traditional risk-based models; the area under curve (AUC) was 0.786 [0.783−0.789], compared with 0.694 [0.690−0.698] (p-value < 0.00001). The presence of acute and chronic respiratory diseases, age, and previous emergency department visits contributed most to the GFlu-CxFlag model’s prediction. When higher numerical scores were assigned to more severe complications, the GFlu-CxFlag AUC increased to 0.828 [0.823−0.833], with excellent discrimination in the final model used to perform the risk stratification of the population. The GFlu-CxFlag can better identify high-risk individuals than existing models based on vaccination guidelines, thus creating a population-based risk stratification for individual risk assessment and deployment in vaccine hesitancy reduction programs in our health system.

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.

The Interaction of Influenza A NS1 and Cellular TRBP Protein Modulates the Function of RNA Interference Machinery

Influenza A virus (IAV), one of the most prevalent respiratory diseases, causes pandemics around the world. The multifunctional non-structural protein 1 (NS1) of IAV is a viral antagonist that suppresses host antiviral response. However, the mechanism by which NS1 modulates the RNA interference (RNAi) pathway remains unclear. Here, we identified interactions between NS1 proteins of Influenza A/PR8/34 (H1N1; IAV-PR8) and Influenza A/WSN/1/33 (H1N1; IAV-WSN) and Dicer’s cofactor TAR-RNA binding protein (TRBP). We found that the N-terminal RNA binding domain (RBD) of NS1 and the first two domains of TRBP protein mediated this interaction. Furthermore, two amino acid residues (Arg at position 38 and Lys at position 41) in NS1 were essential for the interaction. We generated TRBP knockout cells and found that NS1 instead of NS1 mutants (two-point mutations within NS1, R38A/K41A) inhibited the process of microRNA (miRNA) maturation by binding with TRBP. PR8-infected cells showed masking of short hairpin RNA (shRNA)-mediated RNAi, which was not observed after mutant virus-containing NS1 mutation (R38A/K41A, termed PR8/3841) infection. Moreover, abundant viral small interfering RNAs (vsiRNAs) were detected in vitro and in vivo upon PR8/3841 infection. We identify, for the first time, the interaction between NS1 and TRBP that affects host RNAi machinery.

Broad-Spectrum Activity of Small Molecules Acting against Influenza a Virus: Biological and Computational Studies

Influenza still represents a problematic disease, involving millions of people every year and causing hundreds of thousands of deaths. Only a few drugs are clinically available. The search for an effective weapon is still ongoing. In this scenario, we recently identified new drug-like compounds with antiviral activity toward two A/H1N1 Influenza virus strains, which were demonstrated to interfere with the processes mediated by hemagglutinin (HA). In the present work, the compound’s ability to act against the A/H3N2 viral strain has been evaluated in hemagglutination inhibition (HI) assays. Two of the five tested compounds were also active toward the A/H3N2 Influenza virus. To validate the scaffold activity, analogue compounds of two broad-spectrum molecules were selected and purchased for HI testing on both A/H1N1 and A/H3N2 Influenza viruses. Forty-three compounds were tested, and four proved to be active toward all three viral strains. A computational study has been carried out to depict the HA binding process of the most interesting compounds.

The feasibility of pragmatic influenza vaccine randomized controlled real-world trials in Denmark and England

We estimated the frequency of non-specific influenza-associated clinical endpoints to inform the feasibility of pragmatic randomized controlled trials (RCT) assessing relative vaccine effectiveness (rVE). Hospitalization rates of respiratory, cardiovascular and diabetic events were estimated from Denmark and England's electronic databases and stratified by age, comorbidity and influenza vaccination status. We included a seasonal average of 4.5 million Danish and 7.2 million English individuals, 17 and 32% with comorbidities. Annually, approximately 1% of Danish and 0.5% of English individuals were hospitalized for selected events, ~50% of them respiratory. Hospitalization rates were 40-50-fold and 2-10-fold higher in those >50 years and with comorbidities, respectively. Our findings suggest that a pragmatic RCT using non-specific endpoints is feasible. However, for outcomes with rates <2.5%, it would require randomization of ~100,000 participants to have the power to detect a rVE difference of ~13%. Targeting selected groups (older adults, those with comorbidities) where frequency of events is high would improve trial efficiency.

Estimates of mortality associated with seasonal influenza for the European Union from the GLaMOR project

BACKGROUND

The European Centres for Disease Prevention and Control (ECDC) estimates that seasonal influenzacauses 4-50 million symptomatic infections in the EU/EEA each year and 15,000-70,000 European citizens die of causes associated with influenza. We used modelling methods to estimate influenza-associated mortality for the European Union by age group and country.

METHODS

We compiled influenza-associated respiratory mortality estimates for 31 countries around the world (11 countries in the EU) during 2002-2011 (excluding the 2009 pandemic). From these we extrapolated the influenza mortality burden for all 193 countries of the world, including the 28 countries of the EU, using a multiple imputation approach. To study the effect of vaccination programs, we obtained data from the EU-funded VENICE project regarding the percentage of persons over 65 who were vaccinated in each country; the data ranged from 2% to 82% between the 21 countries which provided estimates for the 2006/07 reference season.

RESULTS

We estimated that an average of 27,600 (range 16,200-39,000) respiratory deaths were associated with seasonal influenza in the 28 EU countries per winter; 88% were among people 65 years and older, and the rates of mortality in this age group were roughly 35 times higher compared with those < 65 years. Estimates varied considerably across the EU; for example, rates in the elderly ranged from 21.6 (12.5-35.1) per 100,000 in Portugal to 36.5 (16.4-62.5) in Luxembourg, a difference of nearly 70%. We were unable to find a negative correlation between vaccination coverage rates and influenza-associated mortality estimates in the elderly.

CONCLUSION

Our EU estimate of influenza-associated respiratory mortality is broadly consistent with the ECDC estimate. More research is needed to explain the observed variation in mortality across the EU, and on possible bias that could explain the unexpected lack of mortality benefits associated with European elderly influenza vaccination programs.

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.

Mortality Associated With Influenza and Respiratory Syncytial Virus in the US, 1999-2018

IMPORTANCE

Respiratory syncytial virus (RSV) mortality estimates have not been updated since 2009, and no study has assessed changes in influenza mortality after the 2009 pandemic. Updated burden estimates are needed to characterize long-term changes in the epidemiology of these viruses.

OBJECTIVE

To evaluate excess mortality from RSV and influenza in the US from 1999 to 2018.

DESIGN, SETTING, AND PARTICIPANTS

This cross-sectional study used data from 50.3 million US death certificates from 1999 to 2018 to create age-specific linear regression models and assess weekly mortality fluctuations above a seasonal baseline associated with RSV and influenza. Statistical analysis was performed for 1043 weeks from January 3, 1999, to December 29, 2018.

MAIN OUTCOMES AND MEASURES

Excess mortality associated with RSV and influenza estimated from the difference between observed and expected underlying respiratory mortality each season.

RESULTS

There were 50.3 million death certificates (50.1% women and 49.9% men; mean [SD] age at death, 72.7 [18.6] years) included in this analysis, 1.0% for children younger than 1 year and 73.4% for adults aged 65 years or older. A mean of 6549 (95% CI, 6140-6958) underlying respiratory deaths were associated with RSV annually, including 96 (95% CI, 92-99) deaths among children younger than 1 year. For influenza, there were 10 171 (95% CI, 9652-10 691) underlying respiratory deaths per year, with 23 deaths (95% CI, 19-27) among children younger than 1 year. The highest mean mortality rate per 100 000 population for both viruses was among adults aged 65 years or older at 14.7 (95% CI, 13.8-15.5) for RSV and 20.5 (95% CI, 19.4-21.5) for influenza. A lower proportion of influenza deaths occurred among those aged 65 years or older compared with earlier estimates (75.1% [95% CI, 67.4%-82.8%]). Influenza mortality was highest among those aged 65 years or older in seasons when A/H3N2 predominated (18 739 [95% CI, 16 616-21 336] deaths in 2017-2018) and among those aged 5 to 49 years when A/H1N1pdm2009 predominated (1683 [95% CI, 1583-1787] deaths in 2013-2014). Results were sensitive to the choice of mortality outcome and method, with the broadest outcome associated with annual means of 23 352 (95% CI, 21 814-24 891) excess deaths for RSV and 27 171 (95% CI, 25 142-29 199) for influenza.

CONCLUSIONS AND RELEVANCE

This study suggests that RSV poses a greater risk than influenza to infants, while both are associated with substantial mortality among elderly individuals. Influenza has large interannual variability, affecting different age groups depending on the circulating virus. The emergence of the influenza A/H1N1pdm2009 pandemic virus in 2009 shifted mortality toward middle-aged adults, a trend still observed to date. This study's estimates provide a benchmark to evaluate the mortality benefits associated with interventions against respiratory viruses, including new or improved immunization strategies.

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.

Human Influenza Epidemiology

Influenza virus infections are common in people of all ages. Epidemics occur in the winter months in temperate locations and at varying times of the year in subtropical and tropical locations. Most influenza virus infections cause mild and self-limiting disease, and around one-half of all infections occur with a fever. Only a small minority of infections lead to serious disease requiring hospitalization. During epidemics, the rates of influenza virus infections are typically highest in school-age children. The clinical severity of infections tends to increase at the extremes of age and with the presence of underlying medical conditions, and impact of epidemics is greatest in these groups. Vaccination is the most effective measure to prevent infections, and in recent years influenza vaccines have become the most frequently used vaccines in the world. Nonpharmaceutical public health measures can also be effective in reducing transmission, allowing suppression or mitigation of influenza epidemics and pandemics.

Development of influenza-associated disease burden pyramid in Shanghai, China, 2010-2017: a Bayesian modelling study

OBJECTIVES

Negative estimates can be produced when statistical modelling techniques are applied to estimate morbidity and mortality attributable to influenza. Based on the prior knowledge that influenza viruses are hazardous pathogens and have adverse health outcomes of respiratory and circulatory disease (R&C), we developed an improved model incorporating Bayes' theorem to estimate the disease burden of influenza in Shanghai, China, from 2010 to 2017.

DESIGN

A modelling study using aggregated data from administrative systems on weekly R&C mortality and hospitalisation, influenza surveillance and meteorological data. We constrained the regression coefficients for influenza activity to be positive by truncating the prior distributions at zero.

SETTING

Shanghai, China.

PARTICIPANTS

People registered with R&C deaths (450 298) and hospitalisations (2621 787, from 1 July 2013), and with influenza-like illness (ILI) outpatient visits (342 149) between 4 January 2010 and 31 December 2017.

PRIMARY OUTCOME MEASURES

Influenza-associated disease burden (mortality, hospitalisation and outpatient visit rates) and clinical severity (outpatient-mortality, outpatient-hospitalisation and hospitalisation-mortality risks).

RESULTS

Influenza was associated with an annual average of 15.49 (95% credibility interval (CrI) 9.06-22.06) excess R&C deaths, 100.65 (95% CrI 48.79-156.78) excess R&C hospitalisations and 914.95 (95% CrI 798.51-1023.66) excess ILI outpatient visits per 100 000 population in Shanghai. 97.23% and 80.24% excess R&C deaths and hospitalisations occurred in people aged ≥65 years. More than half of excess morbidity and mortality were associated with influenza A(H3N2) virus, and its severities were 1.65-fold to 3.54-fold and 1.47-fold to 2.16-fold higher than that for influenza A(H1N1) and B viruses, respectively.

CONCLUSIONS

The proposed Bayesian approach with reasonable prior information improved estimates of influenza-associated disease burden. Influenza A(H3N2) virus was generally associated with higher morbidity and mortality, and was relatively more severe compared with influenza A(H1N1) and B viruses. Targeted influenza prevention and control strategies for the elderly in Shanghai may substantially reduce the disease burden.

Excess respiratory mortality and hospitalizations associated with influenza in Australia, 2007-2015

BACKGROUND

Influenza is the most common vaccine-preventable disease in Australia, causing significant morbidity and mortality. We assessed the burden of influenza across all ages in terms of influenza-associated mortality and hospitalizations using national mortality, hospital-discharge and influenza surveillance data.

METHODS

Influenza-associated excess respiratory mortality and hospitalization rates from 2007 to 2015 were estimated using generalized additive models with a proxy of influenza activity based on syndromic and laboratory surveillance data. Estimates were made for each age group and year.

RESULTS

The estimated mean annual influenza-associated excess respiratory mortality was 2.6 per 100 000 population [95% confidence interval (CI): 1.8, 3.4 per 100 000 population]. The excess annual respiratory hospitalization rate was 57.4 per 100 000 population (95% CI: 32.5, 82.2 per 100 000 population). The highest mortality rates were observed among those aged ≥75 years (35.11 per 100 000 population; 95% CI: 19.93, 50.29 per 100 000 population) and hospitalization rates were also highest among older adults aged ≥75 years (302.95 per 100 000 population; 95% CI: 144.71, 461.19 per 100 000 population), as well as children aged <6 months (164.02 per 100 000 population; 95% CI: -34.84, 362.88 per 100 000 population). Annual variation was apparent, ranging from 1.0 to 3.9 per 100 000 population for mortality and 24.2 to 94.28 per 100 000 population for hospitalizations. Influenza A contributed to almost 80% of the average excess respiratory hospitalizations and 60% of the average excess respiratory deaths.

CONCLUSIONS

Influenza causes considerable burden to all Australians. Expected variation was observed among age groups, years and influenza type, with the greatest burden falling to older adults and young children. Understanding the current burden is useful for understanding the potential impact of mitigation strategies, such as vaccination.

Epidemic situation of the complex seasonality of imported influenza A and B virus transmission in Guangxi ports of China

Background/aim

Analysis of the characteristics of influenza virus in imported cases in Guangxi province of China.

Materials and methods

Throat swabs of imported cases with influenza-like symptoms were detected by real-time PCR from July 2016 to December 2019.

Results

1292 laboratory detections of influenza were reported in 3974 influenza-like cases, of which 71.67% (926) were influenza A. The ratio of test positive was 32.82%. The proportion of detections of influenza B was 28.33% (366). A total of 70.51% of the cases mostly came from Vietnam (911). A total of 86.76% (1121) of the cases were imported from Dongxing Port, Nanning Airport, and Pingxiang Port. There was no statistical difference in all age groups. At the same time, 3 of the untyped A-type specimens were sequenced by next-generation sequencing. Among them, the sequences of 2 specimens from Vietnam had high homology with the influenza strain H3N2 in Hong Kong in 2017. The specimen sequence from Thailand is highly homologous to the influenza pandemic strain H1N1 in Brisbane, Australia in 2018.

Conclusion

Imported influenza cases in Guangxi have occurred throughout the year, with higher numbers in winter and spring. The cases mostly came from Vietnam with influenza A. Relevant measures should be taken to control the further spread of the virus.

Global Seasonal Influenza Mortality Estimates: A Comparison of 3 Different Approaches

Prior to updating global influenza-associated mortality estimates, the World Health Organization convened a consultation in July 2017 to understand differences in methodology and implications for results of 3 influenza mortality projects from the US Centers for Disease Control and Prevention (CDC), the Netherlands Institute for Health Service Research's Global Pandemic Mortality Project II (GLaMOR), and the Institute for Health Metrics and Evaluation (IHME). The expert panel reviewed estimates and discussed differences in data sources, analysis, and modeling assumptions. We performed a comparison analysis of the estimates. Influenza-associated respiratory death counts were comparable between CDC and GLaMOR; the IHME estimate was considerably lower. The greatest country-specific influenza-associated fold differences in mortality rate between CDC and IHME estimates and between GLaMOR and IHME estimates were among countries in Southeast Asia and the Eastern Mediterranean region. The data envelope used for the calculation was one of the major differences (CDC and GLaMOR: all respiratory deaths; IHME: lower-respiratory infection deaths). With the assumption that there is only one cause of death for each death, IHME estimates a fraction of the full influenza-associated respiratory mortality that is measured by the other 2 groups. Wide variability of parameters was observed. Continued coordination between groups could assist with better understanding of methodological differences and new approaches to estimating influenza deaths globally.

Public health matters: why is Latin America struggling in addressing the pandemic?

This article examines how Argentina, Brazil, Chile, Colombia, Mexico, and Peru addressed the COVID-19 pandemic and the effectiveness of these policy responses from the date each country declared a sanitary emergency, between middle and late March 2020 to the most recent available measurement on 23 September 2020. To analyze how governments responded to the COVID-19 pandemic in these six Latin American countries, we use an index of government response, created by the University of Oxford. To explore the effects of these governmental mitigation policies on reducing social mobility, we use Google mobility reports. We also analyze how these policies may have influenced COVID-19 mortality rates. Overall, the results showed that both timelier and more stringent implementation of the public policies analyzed to address the COVID-19 pandemic seem to be associated with higher mobility reductions and lower mortality rates. We draw five policy lessons from the way each country implemented these mitigation policies. KEY MESSAGE: Timelier and more stringent implementation of these public policies may contribute to a higher mobility reduction in several public spaces and to lower mortality rates. The effectiveness of the closure and containment policies in each Latin American country seem to depend on the degree of compliance of their respective populations and to their socioeconomic living conditions. Economic and social policies of income support and debt relief provided by governments allowed people to comply with closure and containment policies. Health systems should maintain high levels of policy stringency together with effective surveillance through testing policy and contact tracing.

Influenza-associated disease burden in mainland China: a systematic review and meta-analysis

Influenza causes substantial morbidity and mortality. Many original studies have been carried out to estimate disease burden of influenza in mainland China, while the full disease burden has not yet been systematically reviewed. We did a systematic review and meta-analysis to assess the burden of influenza-associated mortality, hospitalization, and outpatient visit in mainland China. We searched 3 English and 4 Chinese databases with studies published from 2005 to 2019. Studies reporting population-based rates of mortality, hospitalization, or outpatient visit attributed to seasonal influenza were included in the analysis. Fixed-effects or random-effects model was used to calculate pooled estimates of influenza-associated mortality depending on the degree of heterogeneity. Meta-regression was applied to explore the sources of heterogeneity. Publication bias was assessed by funnel plots and Egger’s test. We identified 30 studies eligible for inclusion with 17, 8, 5 studies reporting mortality, hospitalization, and outpatient visit associated with influenza, respectively. The pooled influenza-associated all-cause mortality rates were 14.33 and 122.79 per 100,000 persons for all ages and ≥ 65 years age groups, respectively. Studies were highly heterogeneous in aspects of age group, cause of death, statistical model, geographic location, and study period, and these factors could explain 60.14% of the heterogeneity in influenza-associated mortality. No significant publication bias existed in estimates of influenza-associated all-cause mortality. Children aged < 5 years were observed with the highest rates of influenza-associated hospitalizations and ILI outpatient visits. People aged ≥ 65 years and < 5 years contribute mostly to mortality and morbidity burden due to influenza, which calls for targeted vaccination policy for older adults and younger children in mainland China.

Adjuvanted Influenza Vaccines Elicits Higher Antibody Responses against the A(H3N2) Subtype than Non-Adjuvanted Vaccines

BACKGROUND

vaccination is the best approach to prevent influenza infections so far. Serological studies on the effect of different vaccine types are important to address vaccination campaigns and protect our population. In our study, we compared the serological response against influenza A subtypes using the non-adjuvanted influenza vaccine (NAIV) in adults and the elderly and the adjuvanted influenza vaccine (AIV) in the elderly.

METHODS

We performed a retrospective analysis by hemagglutination inhibition assay (HI) of serum samples right before and 28 days after seasonal influenza vaccination during the 1996-2017 seasons.

CONCLUSIONS

The AIV presents better performance against the A(H3N2) subtype in the elderly whereas the NAIV induces a better response against A(H1N1)pdm09 in the same group.

A multivariate analysis of risk factors associated with death by Covid-19 in the USA, Italy, Spain, and Germany

Aim

Our aim was to investigate the risk factors associated with death from COVID-19 in four countries: The USA, Italy, Spain, and Germany.

Subject and methods

We used data from the Institute for Health Metrics and Evaluation with projection information from January–August 2020. A multivariate analysis of logistic regression was performed. The following factors were analyzed (per day): number of beds needed for the hospital services, number of intensive care units (ICU) beds required, number of ventilation devices, number of both hospital and ICU admissions due to COVID-19. Nagelkerke’s R² coefficient of determination was used to evaluate the model’s predictive ability. The quality of the model’s fit was assessed by the Hosmer–Lemeshow and the chi-square tests.

Results

Among the evaluated countries, Italy presented greater need for ICU beds/day (≤ 98; OR = 2315.122; CI 95% [334.767–16,503.502]; p < 0.001) and daily ventilation devices (≤ 118; OR = 1784.168; CI 95% [250.217–12,721.995]; p < 0.001). It is expected that both Italy and Spain have a higher ICU admission rate due to COVID-19 (n = 14/day). Spain will need more beds/day (≤ 357; OR = 146.838; CI 95% [113.242–190.402]; p  < 0.001) and probably will have a higher number of daily hospital admissions (n = 48/day). All the above-mentioned factors have an important impact on patients’ mortality due to COVID-19 in all four countries.

Conclusions

Further investments in hospitals’ infrastructure, as well as the development of innovative devices for patient’s ventilation, are paramount to fight the pandemic in the USA, Italy, Spain, and Germany.

Monitoring the mortality impact of COVID-19 in Europe: What can be learned from 2009 influenza H1N1p mortality studies?

OBJECTIVES

Understanding the proportion of pandemic deaths captured as 'laboratory-confirmed' deaths is crucial. We assessed the ability of laboratory-confirmed deaths to capture mortality in the EU during the 2009 pandemic, and examined the likelihood that these findings are applicable to the SARS-CoV-2 pandemic.

METHODS

We present unpublished results from the Global Pandemic Mortality (GLaMOR) project, in which country-specific mortality estimates were made for the 2009 influenza H1N1p pandemic. These estimates were compared with laboratory-confirmed deaths during the 2009 pandemic to estimate the ability of surveillance systems to capture pandemic mortality.

RESULTS

For the 2009 influenza H1N1p pandemic, we estimated that the proportion of true pandemic deaths captured by laboratory-confirmed deaths was approximately 67%. Several differences between the two pandemics (e.g. age groups affected) make it unlikely that this capture rate will be equally high for SARS-CoV-2.

CONCLUSION

The surveillance of laboratory-confirmed deaths in the EU during the 2009 pandemic was more accurate than previously assumed. We hypothesize that this method is less reliable for SARS-CoV-2. Near-real-time excess all-cause mortality estimates, routinely compiled by EuroMOMO, probably offer a better indicator of pandemic mortality. We urge more countries to join this project and that national-level absolute mortality numbers are presented.

Correlation of COVID-19 Pandemic with Healthcare System Response and Prevention Measures in Saudi Arabia

BACKGROUND

The Saudi government has taken the decision to prevent the entrance of about 2.5 million international pilgrims seeking to perform hajj in order to protect the world from a catastrophic widespread of disease. Moreover, health systems in Saudi Arabia are offering free testing for residents whether Saudi and non-Saudi.

OBJECTIVE

This study aimed to evaluate the spread of COVID-19 associated with preventive measures taken in Saudi Arabia and to develop a detailed COVID-19 prevention strategy as a framework for the Saudi Arabia community.

METHODOLOGY

Population size and age distributions among the country of Saudi Arabia were taken from the 2020 World Population Prospects. Contact patterns were measured using the Saudi Arabia Ministry of Health Statistical Annual Report.

CONCLUSIONS

Our study demonstrates that performing screening tests as early as possible to facilitate the rapid detection of infected cases, fast treatment, and instant isolation for suspected cases is the most definitive rejoinder for public health. Moreover, our study revealed the significance of performing preventive measures in reducing infection and death rates around Saudi Arabia by 27%, while in other countries, it reduced the death rate ranging from 10-73%. This study provides an achievable strategy for prevention and early detection of COVID-19 spread.

The Effect of Influenza Vaccination History on Changes in Hemagglutination Inhibition Titers After Receipt of the 2015-2016 Influenza Vaccine in Older Adults in Hong Kong

BACKGROUND

Immune responses to influenza vaccination can be weaker in older adults than in other age groups. We hypothesized that antibody responses would be particularly weak among repeat vaccinees when the current and prior season vaccine components are the same.

METHODS

An observational study was conducted among 827 older adults (aged ≥75 years) in Hong Kong. Serum samples were collected immediately before and 1 month after receipt of the 2015-2016 quadrivalent inactivated influenza vaccine. We measured antibody titers with the hemagglutination inhibition assay and compared the mean fold rise from prevaccination to postvaccination titers and the proportions with postvaccination titers ≥40 or ≥160.

RESULTS

Participants who reported receipt of vaccination during either of the previous 2 years had a lower mean fold rise against all strains than with those who did not. Mean fold rises for A(H3N2) and B/Yamagata were particularly weak after repeated vaccination with the same vaccine strain, but we did not generally find significant differences in the proportions of participants with postvaccination titers ≥40 and ≥160.

CONCLUSIONS

Overall, we found that reduced antibody responses in repeat vaccinees were particularly reduced among older adults who had received vaccination against the same strains in preceding years.

Mortality attributable to seasonal influenza in Greece, 2013 to 2017: variation by type/subtype and age, and a possible harvesting effect

IntroductionEstimating the contribution of influenza to excess mortality in the population presents substantial methodological challenges.AimIn a modelling study we combined environmental, epidemiological and laboratory surveillance data to estimate influenza-attributable mortality in Greece, over four seasons (2013/14 to 2016/17), specifically addressing the lag dimension and the confounding effect of temperature.MethodsAssociations of influenza type/subtype-specific incidence proxies and of daily mean temperature with mortality were estimated with a distributed-lag nonlinear model with 30 days of maximum lag, separately by age group (all ages, 15-64 and ≥ 65 years old). Total and weekly deaths attributable to influenza and cold temperatures were calculated.ResultsOverall influenza-attributable mortality was 23.6 deaths per 100,000 population per year (95% confidence interval (CI): 17.8 to 29.2), and varied greatly between seasons, by influenza type/subtype and by age group, with the vast majority occurring in persons aged ≥ 65 years. Most deaths were attributable to A(H3N2), followed by influenza B. During periods of A(H1N1)pdm09 circulation, weekly attributable mortality to this subtype among people ≥ 65 years old increased rapidly at first, but then fell to zero and even negative, suggesting a mortality displacement (harvesting) effect. Mortality attributable to cold temperatures was much higher than that attributable to influenza.ConclusionsStudies of influenza-attributable mortality need to consider distributed-lag effects, stratify by age group and adjust both for circulating influenza virus types/subtypes and daily mean temperatures, in order to produce reliable estimates. Our approach addresses these issues, is readily applicable in the context of influenza surveillance, and can be useful for other countries.

The burden of influenza and pneumonia mortality attributable to absolute humidity among elderly people in Chongqing, China, 2012-2018

OBJECTIVE

To examine the association between absolute humidity (AH) and influenza and pneumonia (P&I) mortality, and to quantify P&I mortality burden attributable to non-optimum AHs among elderly people aged ≥65 years in Chongqing, the largest municipality of China.

METHODS

Daily data of P&I mortality from 2012 to 2018, and the contemporaneous meteorological data in the study area were collected. Distributed lag non-linear model (DLNM) was applied to estimate the non-linear and delayed effects of absolute humidity (AH) on P&I mortality. Then, attributable deaths were calculated for the dry and moist AH, defined as AH below and above the minimum mortality AH (MMAH), respectively. Moderate and extreme AHs were defined using cutoffs at the 2.5th and 97.5th percentiles of AH.

RESULTS

The relationship between AH and P&I mortality was a U-shaped curve. The MMAH was 11.5 g/m³ (46.4th percentile). In total, 25.7% (95% confidence interval: 10.0-38.2) of P&I mortality (4673 deaths) was attributed to non-optimum AHs. Low AHs were responsible for 12.7% of the P&I death burden (95%CI: 0.2-20.1), while high AHs for 13.0% (95%CI: -9.4-25.7). Extreme low and high AHs accounted for 3.7% (95%CI: 0.1-6.8) and 3.0% (95%CI: 0-5.4) of P&I mortality.

CONCLUSIONS

Our study showed that both low AHs and high AHs are responsible for considerable AH-related P&I mortality burden among elderly people. Our results may have important public health implications for the development of relevant intervention policies to reduce P&I deaths among the elderly.

Mortality burden from seasonal influenza in Chongqing, China, 2012-2018

Purpose

To estimate influenza-associated excess mortality rates (EMRs) in Chongqing from 2012 to 2018.

Methods

We obtained weekly mortality data for all-cause and four underlying causes of death (circulatory and respiratory disease (CRD), pneumonia and influenza (P&I), chronic obstructive pulmonary disease (COPD) and ischemic heart disease (IDH)), and influenza surveillance data, from 2012 to 2018. A negative-binomial regression model was used to estimate influenza-associated EMRs in two age groups (<65 years and ≥65 years).

Results

It was estimated that an annual average of 10025 influenza-associated deaths occurred in Chongqing, corresponding to 5.2% of all deaths. The average EMR for all-cause death associated with influenza was 33.5 (95% confidence interval (CI): 31.5–35.6) per 100 000 persons, and in separate cause-specific models we attributed 24.7 (95% CI: 23.3–26.0), 0.8 (95% CI: 0.7–0.8), 8.5 (95% CI: 8.1–9.0) and 5.0 (95% CI: 4.7–5.3) per 100 000 persons EMRs to CRD, P&I, COPD and IDH, respectively. The estimated EMR for influenza B virus was 20.6 (95% CI: 20.3–21.0), which was significantly higher than the rates of 5.3 (95% CI: 4.5–6.1) and 7.5 (95% CI: 6.7–8.3) for A(H3N2) and A(H1N1) pdm09 virus, respectively. The estimated EMR was 152.3 (95% CI: 136.1–168.4) for people aged ≥65 years, which was significantly higher than the rate for those aged <65 years (6.8, 95% CI: 6.3–7.2).

Conclusions

Influenza was associated with substantial EMRs in Chongqing, especially among elderly people. Influenza B virus caused a relatively higher excess mortality impact compared with A(H1N1)pdm09 and A(H3N2). It is advisable to optimize future seasonal influenza vaccine reimbursement policy in Chongqing to curb disease burden.

[Epidemiology and control of COVID-19]

The Coronavirus Disease Pandemic 2019 (COVID-19), caused by the Severe Acute Respiratory Syndrome-related Coronavirus 2 (SARS-CoV-2), started in December 2019 in China. SARS-CoV-2 is easily transmitted by droplet infection. After an incubation period of 1-14 days, COVID-19 shows a mild course in 80 % of observed cases and a severe course in 20 %, with a lethality rate of 0.3-5.8 %. Elderly people and people with underlying diseases have a higher risk of severe courses with mandatory ventilation. So far there are neither effective drugs nor vaccinations available, so only public health interventions such as physical distancing and hygiene measures on the one hand and targeted testing followed by isolation and quarantine measures on the other hand are available. China has shown that maximum use of these measures can control the epidemic. The further course and also the consequences for the global economy cannot be clearly predicted at present.

Real-time estimation of the influenza-associated excess mortality in Hong Kong

Statistical models are commonly employed in the estimation of influenza-associated excess mortality that, due to various reasons, is often underestimated by laboratory-confirmed influenza deaths reported by healthcare facilities. However, methodology for timely and reliable estimation of that impact remains limited because of the delay in mortality data reporting. We explored real-time estimation of influenza-associated excess mortality by types/subtypes in each year between 2012 and 2018 in Hong Kong using linear regression models fitted to historical mortality and influenza surveillance data. We could predict that during the winter of 2017/2018, there were ~634 (95% confidence interval (CI): (190, 1033)) influenza-associated excess all-cause deaths in Hong Kong in population ⩾18 years, compared to 259 reported laboratory-confirmed deaths. We estimated that influenza was associated with substantial excess deaths in older adults, suggesting the implementation of control measures, such as administration of antivirals and vaccination, in that age group. The approach that we developed appears to provide robust real-time estimates of the impact of influenza circulation and complement surveillance data on laboratory-confirmed deaths. These results improve our understanding of the impact of influenza epidemics and provide a practical approach for a timely estimation of the mortality burden of influenza circulation during an ongoing epidemic.

Global burden of respiratory infections associated with seasonal influenza in children under 5 years in 2018: a systematic review and modelling study

BACKGROUND

Seasonal influenza virus is a common cause of acute lower respiratory infection (ALRI) in young children. In 2008, we estimated that 20 million influenza-virus-associated ALRI and 1 million influenza-virus-associated severe ALRI occurred in children under 5 years globally. Despite this substantial burden, only a few low-income and middle-income countries have adopted routine influenza vaccination policies for children and, where present, these have achieved only low or unknown levels of vaccine uptake. Moreover, the influenza burden might have changed due to the emergence and circulation of influenza A/H1N1pdm09. We aimed to incorporate new data to update estimates of the global number of cases, hospital admissions, and mortality from influenza-virus-associated respiratory infections in children under 5 years in 2018.

METHODS

We estimated the regional and global burden of influenza-associated respiratory infections in children under 5 years from a systematic review of 100 studies published between Jan 1, 1995, and Dec 31, 2018, and a further 57 high-quality unpublished studies. We adapted the Newcastle-Ottawa Scale to assess the risk of bias. We estimated incidence and hospitalisation rates of influenza-virus-associated respiratory infections by severity, case ascertainment, region, and age. We estimated in-hospital deaths from influenza virus ALRI by combining hospital admissions and in-hospital case-fatality ratios of influenza virus ALRI. We estimated the upper bound of influenza virus-associated ALRI deaths based on the number of in-hospital deaths, US paediatric influenza-associated death data, and population-based childhood all-cause pneumonia mortality data in six sites in low-income and lower-middle-income countries.

FINDINGS

In 2018, among children under 5 years globally, there were an estimated 109·5 million influenza virus episodes (uncertainty range [UR] 63·1-190·6), 10·1 million influenza-virus-associated ALRI cases (6·8-15·1); 870 000 influenza-virus-associated ALRI hospital admissions (543 000-1 415 000), 15 300 in-hospital deaths (5800-43 800), and up to 34 800 (13 200-97 200) overall influenza-virus-associated ALRI deaths. Influenza virus accounted for 7% of ALRI cases, 5% of ALRI hospital admissions, and 4% of ALRI deaths in children under 5 years. About 23% of the hospital admissions and 36% of the in-hospital deaths were in infants under 6 months. About 82% of the in-hospital deaths occurred in low-income and lower-middle-income countries.

INTERPRETATION

A large proportion of the influenza-associated burden occurs among young infants and in low-income and lower middle-income countries. Our findings provide new and important evidence for maternal and paediatric influenza immunisation, and should inform future immunisation policy particularly in low-income and middle-income countries.

FUNDING

WHO; Bill & Melinda Gates Foundation.

The COVID-19 epidemic, its mortality, and the role of non-pharmaceutical interventions

COVID-19 has developed into a pandemic, hitting hard on our communities. As the pandemic continues to bring health and economic hardship, keeping mortality as low as possible will be the highest priority for individuals; hence governments must put in place measures to ameliorate the inevitable economic downturn. The course of an epidemic may be defined by a series of key factors. In the early stages of a new infectious disease outbreak, it is crucial to understand the transmission dynamics of the infection. The basic reproduction number (R0), which defines the mean number of secondary cases generated by one primary case when the population is largely susceptible to infection ('totally naïve'), determines the overall number of people who are likely to be infected, or, more precisely, the area under the epidemic curve. Estimation of changes in transmission over time can provide insights into the epidemiological situation and identify whether outbreak control measures are having a measurable effect. For R0 > 1, the number infected tends to increase, and for R0 < 1, transmission dies out. Non-pharmaceutical strategies to handle the epidemic are sketched and based on current knowledge, the current situation is sketched and scenarios for the near future discussed.

Burden of influenza-associated outpatient influenza-like illness consultations in China, 2006-2015: A population-based study

BACKGROUND

Human influenza virus infections cause a considerable burden of morbidity and mortality worldwide each year. Understanding regional influenza-associated outpatient burden is crucial for formulating control strategies against influenza viruses.

METHODS

We extracted the national sentinel surveillance data on outpatient visits due to influenza-like-illness (ILI) and virological confirmation of sentinel specimens from 30 provinces of China from 2006 to 2015. Generalized additive regression models were fitted to estimate influenza-associated excess ILI outpatient burden for each individual province, accounting for seasonal baselines and meteorological factors.

RESULTS

Influenza was associated with an average of 2.5 excess ILI consultations per 1000 person-years (py) in 30 provinces of China each year from 2006 to 2015. Influenza A(H1N1)pdm09 led to a higher number of influenza-associated ILI consultations in 2009 across all provinces compared with other years. The excess ILI burden was 4.5 per 1000 py among children aged below 15 years old, substantially higher than that in adults.

CONCLUSIONS

Human influenza viruses caused considerable impact on population morbidity, with a consequent healthcare and economic burden. This study provided the evidence for planning of vaccination programs in China and a framework to estimate burden of influenza-associated outpatient consultations.

Global mortality associated with seasonal influenza epidemics: New burden estimates and predictors from the GLaMOR Project

Background

Until recently, the World Health Organization (WHO) estimated the annual mortality burden of influenza to be 250 000 to 500 000 all-cause deaths globally; however, a 2017 study indicated a substantially higher mortality burden, at 290 000-650 000 influenza-associated deaths from respiratory causes alone, and a 2019 study estimated 99 000-200 000 deaths from lower respiratory tract infections directly caused by influenza. Here we revisit global and regional estimates of influenza mortality burden and explore mortality trends over time and geography.

Methods

We compiled influenza-associated excess respiratory mortality estimates for 31 countries representing 5 WHO regions during 2002-2011. From these we extrapolated the influenza burden for all 193 countries of the world using a multiple imputation approach. We then used mixed linear regression models to identify factors associated with high seasonal influenza mortality burden, including influenza types and subtypes, health care and socio-demographic development indicators, and baseline mortality levels.

Results

We estimated an average of 389 000 (uncertainty range 294 000-518 000) respiratory deaths were associated with influenza globally each year during the study period, corresponding to ~ 2% of all annual respiratory deaths. Of these, 67% were among people 65 years and older. Global burden estimates were robust to the choice of countries included in the extrapolation model. For people <65 years, higher baseline respiratory mortality, lower level of access to health care and seasons dominated by the A(H1N1)pdm09 subtype were associated with higher influenza-associated mortality, while lower level of socio-demographic development and A(H3N2) dominance was associated with higher influenza mortality in adults ≥65 years.

Conclusions

Our global estimate of influenza-associated excess respiratory mortality is consistent with the 2017 estimate, despite a different modelling strategy, and the lower 2019 estimate which only captured deaths directly caused by influenza. Our finding that baseline respiratory mortality and access to health care are associated with influenza-related mortality in persons <65 years suggests that health care improvements in low and middle-income countries might substantially reduce seasonal influenza mortality. Our estimates add to the body of evidence on the variation in influenza burden over time and geography, and begin to address the relationship between influenza-associated mortality, health and development.

Association between type-specific influenza circulation and incidence of severe laboratory-confirmed cases; which subtype is the most virulent?

OBJECTIVES

Excess population mortality during winter is most often associated with influenza A(H3N2), though susceptibility differs by age. We examined differences between influenza types/subtypes in their association with severe laboratory-confirmed cases, overall and by age group, to determine which type is the most virulent.

METHODS

We used nine seasons of comprehensive nationwide surveillance data from Greece (2010-2011 to 2018-2019) to examine the association, separately for influenza A(H1N1)pdm09, A(H3N2) and B, between the number of laboratory-confirmed severe cases (intensive care hospitalizations or deaths) per type/subtype and the overall type-specific circulation during the season (expressed as a cumulative incidence proxy). Quasi-Poisson models with identity link were used, and multiple imputation to handle missing influenza A subtype.

RESULTS

For the same level of viral circulation and across all ages, influenza A(H1N1)pdm09 was associated with twice as many intensive care hospitalizations as A(H3N2) (rate ratio (RR) 1.89, 95% CI 1.38-2.74) and three times more than influenza B (RR 3.27, 95%CI 2.54-4.20). Similar associations were observed for laboratory-confirmed deaths. A(H1N1)pdm09 affected adults over 40 years at similar rates, whereas A(H3N2) affected elderly people at a much higher rate than younger persons (≥65 vs. 40-64 years, RR for intensive care 5.42, 95% CI 3.45-8.65, and RR for death 6.19, 95%CI 4.05-9.38). Within the 40-64 years age group, A(H1N1)pdm09 was associated with an approximately five times higher rate of severe disease than both A(H3N2) and B.

DISCUSSION

Influenza A(H1N1)pdm09 is associated with many more severe laboratory-confirmed cases, likely due to a more typical clinical presentation and younger patient age, leading to more testing. A(H3N2) affects older people more, with cases less often recognized and confirmed.

Influenza-associated excess respiratory mortality in China, 2010-15: a population-based study

BACKGROUND

The estimation of influenza-associated excess mortality in countries can help to improve estimates of the global mortality burden attributable to influenza virus infections. We did a study to estimate the influenza-associated excess respiratory mortality in mainland China for the 2010-11 through 2014-15 seasons.

METHODS

We obtained provincial weekly influenza surveillance data and population mortality data for 161 disease surveillance points in 31 provinces in mainland China from the Chinese Center for Disease Control and Prevention for the years 2005-15. Disease surveillance points with an annual average mortality rate of less than 0·4% between 2005 and 2015 or an annual mortality rate of less than 0·3% in any given years were excluded. We extracted data for respiratory deaths based on codes J00-J99 under the tenth edition of the International Classification of Diseases. Data on respiratory mortality and population were stratified by age group (age <60 years and ≥60 years) and aggregated by province. The overall annual population data of each province and national annual respiratory mortality data were compiled from the China Statistical Yearbook. Influenza surveillance data on weekly proportion of samples testing positive for influenza virus by type or subtype for 31 provinces were extracted from the National Sentinel Hospital-based Influenza Surveillance Network. We estimated influenza-associated excess respiratory mortality rates between the 2010-11 and 2014-15 seasons for 22 provinces with valid data in the country using linear regression models. Extrapolation of excess respiratory mortality rates was done using random-effect meta-regression models for nine provinces without valid data for a direct estimation of the rates.

FINDINGS

We fitted the linear regression model with the data from 22 of 31 provinces in mainland China, representing 83·0% of the total population. We estimated that an annual mean of 88 100 (95% CI 84 200-92 000) influenza-associated excess respiratory deaths occurred in China in the 5 years studied, corresponding to 8·2% (95% CI 7·9-8·6) of respiratory deaths. The mean excess respiratory mortality rates per 100 000 person-seasons for influenza A(H1N1)pdm09, A(H3N2), and B viruses were 1·6 (95% CI 1·5-1·7), 2·6 (2·4-2·8), and 2·3 (2·1-2·5), respectively. Estimated excess respiratory mortality rates per 100 000 person-seasons were 1·5 (95% CI 1·1-1·9) for individuals younger than 60 years and 38·5 (36·8-40·2) for individuals aged 60 years or older. Approximately 71 000 (95% CI 67 800-74 100) influenza-associated excess respiratory deaths occurred in individuals aged 60 years or older, corresponding to 80% of such deaths.

INTERPRETATION

Influenza was associated with substantial excess respiratory mortality in China between 2010-11 and 2014-15 seasons, especially in older adults aged at least 60 years. Continuous and high-quality surveillance data across China are needed to improve the estimation of the disease burden attributable to influenza and the best public health interventions are needed to curb this burden.

FUNDING

National Science Fund for Distinguished Young Scholars, National Science and Technology Major Project of China, National Institute of Health Research, the Harvard Center for Communicable Disease Dynamics from the National Institute of General Medical Sciences, and the China-US Collaborative Program on Emerging and Re-emerging Infectious Disease.

Use of an Influenza Antigen Microarray to Measure the Breadth of Serum Antibodies Across Virus Subtypes

The influenza virus remains a significant cause of mortality worldwide due to the limited effectiveness of currently available vaccines. A key challenge to the development of universal influenza vaccines is high antigenic diversity resulting from antigenic drift. Overcoming this challenge requires novel research tools to measure the breadth of serum antibodies directed against many virus strains across different antigenic subtypes. Here, we present a protocol for analyzing the breadth of serum antibodies against diverse influenza virus strains using a protein microarray of influenza antigens. This influenza antigen microarray is constructed by printing purified hemagglutinin and neuraminidase antigens onto a nitrocellulose-coated membrane using a microarray printer. Human sera are incubated on the microarray to bind antibodies against the influenza antigens. Quantum-dot-conjugated secondary antibodies are used to simultaneously detect IgG and IgA antibodies binding to each antigen on the microarray. Quantitative antibody binding is measured as fluorescence intensity using a portable imager. Representative results are shown to demonstrate assay reproducibility in measuring subtype-specific and cross-reactive influenza antibodies in human sera. Compared to traditional methods such as ELISA, the influenza antigen microarray provides a high throughput multiplexed approach capable of testing hundreds of sera for multiple antibody isotypes against hundreds of antigens in a short time frame, and thus has applications in sero-surveillance and vaccine development. A limitation is the inability to distinguish binding antibodies from neutralizing antibodies.

Estimating age-specific influenza-associated asthma morbidity in Ontario, Canada

BACKGROUND

There is a need to quantify the potential benefits of influenza-focused interventions in reducing asthma morbidity at a population level. This study aims to estimate age-specific annual excess asthma morbidity attributable to influenza in Ontario, Canada.

METHODS

Weekly counts of hospitalizations, emergency department (ED) visits and outpatient physician office visits for asthma were obtained from health administrative data in Ontario from 2010 to 2015, for ages 0-14, 15-59 and 60+. Asthma morbidity was modelled as a function of influenza A and B activity using linear regression, controlling for seasonal and long-term trend, mean temperature and respiratory syncytial virus. Excess asthma morbidity attributable to influenza was calculated as the difference between full model predictions and model predictions with influenza A and B variables set to 0.

RESULTS

Annually, influenza was associated with the following rates of excess asthma morbidity, per 100,000 people with prevalent asthma: 12.5 hospitalizations for ages 15-59 (95% confidence interval (CI): 1.1-23.5); 35.7 hospitalizations for ages 60+ (95% CI: 3.3-67.1); 114.1 ED visits for ages 15-59 (95% CI: 46.9-181.6); 154.6 ED visits for ages 60+ (95% CI: 86.7-223.3); and 1025.7 outpatient physician office visits for ages 60+ (95% CI: 79.0-1877.3).

CONCLUSIONS

Influenza was associated with excess asthma hospitalizations and ED visits for ages 15-59 and 60+ and outpatient physician office visits for ages 60+. Individuals with asthma aged 15-59 and 60+ might be important targets for influenza-focused interventions, to reduce asthma morbidity at the population level.

Outcome prediction using the Mortality in Emergency Department Sepsis score combined with procalcitonin for influenza patients

BACKGROUND

Severe influenza is often associated with bacterial coinfection and can trigger sepsis, which increases the severity, complexity and mortality of the disease. To determine an effective method for predicting 28-day mortality of emergency department (ED) patients with influenza, we investigated the Mortality in Emergency Department Sepsis (MEDS) score, procalcitonin (PCT) and other relevant biomarkers.

METHODS

We conducted a retrospective, observational, monocentric study, and the endpoint was 28-day mortality. Independent predictors were identified and a new combination predictive model was created both by logistic regression, and the model was evaluated by a receiver operating characteristic (ROC) curve.

RESULTS

A total of 364 consecutive ED admitted patients with influenza were enrolled and 45 patients died within 28 days. For predicting 28-day mortality, the MEDS score and PCT were independent predictors with adjusted odds ratio of 1.318 (95% CI 1.206-1.439) and 1.038 (95% CI 1.010-1.065), and with AUCs of 0.817 (95% CI 0.756-0.878) and 0.793 (95% CI 0.725-0.861), respectively. The new combination of the MEDS score with PCT significantly improved the efficacy for predicting 28-day mortality with an AUC of 0.857 (95% CI 0.809-0.905), and was superior to the SOFA score with an AUC of 0.837 (95% CI 0.779-0.894).

CONCLUSION

The MEDS score and PCT, especially when combined, perform well for predicting mortality of ED admitted patients with influenza.

RNA Modulates the Interaction between Influenza A Virus NS1 and Human PABP1

Nonstructural protein 1 (NS1) is a multifunctional protein involved in preventing host-interferon response in influenza A virus (IAV). Previous studies have indicated that NS1 also stimulates the translation of viral mRNA by binding to conserved sequences in the viral 5'-UTR. Additionally, NS1 binds to poly(A) binding protein 1 (PABP1) and eukaryotic initiation factor 4G (eIF4G). The interaction of NS1 with the viral 5'-UTR, PABP1, and eIF4G has been suggested to specifically enhance the translation of viral mRNAs. In contrast, we report that NS1 does not directly bind to sequences in the viral 5'-UTR, indicating that NS1 is not responsible for providing the specificity to stimulate viral mRNA translation. We also monitored the interaction of NS1 with PABP1 using a new, quantitative FRET assay. Our data show that NS1 binds to PABP1 with high affinity; however, the binding of double-stranded RNA (dsRNA) to NS1 weakens the binding of NS1 to PABP1. Correspondingly, the binding of PABP1 to NS1 weakens the binding of NS1 to double-stranded RNA (dsRNA). In contrast, the affinity of PABP1 for binding to poly(A) RNA is not significantly changed by NS1. We propose that the modulation of NS1·PABP1 interaction by dsRNA may be important for the viral cycle.

Incidence of influenza A(H3N2) virus infections in Hong Kong in a longitudinal sero-epidemiological study, 2009-2015

Background

Many serologic studies were done during and after the 2009 influenza pandemic, to estimate the cumulative incidence of influenza A(H1N1)pdm09 virus infections, but there are few comparative estimates of the incidence of influenza A(H3N2) virus infections during epidemics.

Methods

We conducted a longitudinal serologic study in Hong Kong. We collected sera annually and tested samples from 2009–13 by HAI against the A/Perth/16/2009(H3N2) virus, and samples from 2013–15 against the A/Victoria/361/2011(H3N2) virus using the hemagglutination inhibition (HAI) assay. We estimated the cumulative incidence of infections based on 4-fold or greater rises in HAI titers in consecutive sera.

Results

There were four major H3N2 epidemics: (1) Aug-Oct 2010; (2) Mar-Jun 2012; (3) Jul-Oct 2013; and (4) Jun-Jul 2014. Between 516 and 619 relevant pairs of sera were available for each epidemic. We estimated that 9%, 19%, 7% and 7% of the population were infected in each epidemic, respectively, with higher incidence in children in epidemics 1 and 4.

Conclusions

We found that re-infections in each of the four H3N2 epidemics that occurred from 2010 through 2014 were rare. The largest H3N2 epidemic occurred with the lowest level of pre-epidemic immunity.

Influenza-associated mortality in Yancheng, China, 2011-15

INTRODUCTION

The Yangtze river delta in eastern China, centered on Shanghai, is one of the most populated regions of the world with more than 100 million residents. We examined the impact of influenza on excess mortality in Yancheng, a prefecture-level city with 8.2 million population located 250 km north of Shanghai, during 2011-2015.

METHODS

We obtained individual data on deaths by date, age, sex, and cause in Yancheng from the Chinese Centers for Disease Control and Prevention, and used these to derive weekly rates of mortality from respiratory causes, respiratory and cardiovascular causes combined, and all causes. We used data on influenza-like illnesses and laboratory detections of influenza to construct a proxy measure of the weekly incidence of influenza virus infections in the community. We used regression models to estimate the association of influenza activity with mortality and excess mortality by age, cause, and influenza type/subtype.

RESULTS

We estimated that an annual average of 4.59 (95% confidence interval: 3.94, 7.41) excess respiratory deaths per 100 000 persons were associated with influenza, which was 4.6% of all respiratory deaths in the years studied. Almost all influenza-associated excess deaths occurred in persons ≥65 years. Influenza A(H3N2) had the greatest impact on mortality and was associated with around 50% of the influenza-associated respiratory deaths in the 5 years studied.

CONCLUSIONS

Influenza has a substantial impact on respiratory mortality in Yancheng, mainly in older adults. Influenza vaccination has the potential to reduce disease burden, and cost-effectiveness analysis could be used to compare policy options.