Attributable deaths due to influenza: a comparative study of seasonal and pandemic influenza

Spotlight influenza: Laboratory-confirmed seasonal influenza in people with acute respiratory illness: a literature review and meta-analysis, WHO European Region, 2004 to 2017

BackgroundAcross the World Health Organization European Region, there are few estimates of the proportion of people seeking medical care for influenza-like illness or acute respiratory infections and who have laboratory-confirmed seasonal influenza infection.MethodsWe conducted a meta-analysis of data extracted from studies published between 2004 and 2017 and from sentinel data from the European surveillance system (TESSy) between 2004 and 2018. We pooled within-season estimates by influenza type/subtype, setting (outpatient (OP)/inpatient (IP)) and age group to estimate the proportion of people tested who have laboratory-confirmed and medically-attended seasonal influenza in Europe.ResultsIn the literature review, the pooled proportion for all influenza types was 33% (95% confidence interval (CI): 30-36), higher among OP 36% (95% CI: 33-40) than IP 24% (95% CI: 20-29). Pooled estimates for all influenza types by age group were: 0-17 years, 26% (22-31); 18-64 years, 41% (32-50); ≥ 65 years, 33% (27-40). From TESSy data, 33% (31-34) of OP and 24% (21-27) of IP were positive. The highest proportion of influenza A was in people aged 18-64 years (22%, 16-29). By subtype, A(H1N1)pdm09 was highest in 18-64 year-olds (16%, 11-21%) whereas A(H3N2) was highest in those ≥ 65 years (10%, 2-22). For influenza B, the highest proportion of infections was in those aged 18-64 years (15%, 9-24).ConclusionsLaboratory-confirmed influenza accounted for approximately one third of all acute respiratory infections for which medical care was sought during the influenza season.

Utility of Healthcare System-Based Interventions in Improving the Uptake of Influenza Vaccination in Healthcare Workers at Long-Term Care Facilities: A Systematic Review

Healthcare workers (HCWs) in long-term care facilities (LTCFs) can represent a source of influenza infection for the elderly. While flu vaccination coverage (VC) is satisfactory in the elderly, HCWs are less likely to be vaccinated. There is no definitive evidence on which types of healthcare system-based interventions at LTCFs would be more useful in improving the vaccination uptake among HCWs. We performed a systematic review in different databases (Pubmed, Cochrane Database of Systematic Reviews, Health Evidence, Web of Science, Cinahl) to provide a synthesis of the available studies on this topic. Among the 1177 articles screened by their titles and abstracts, 27 were included in this review. Most of the studies reported multiple interventions addressed to improve access to vaccination, eliminate individual barriers, or introduce policy interventions. As expected, mandatory vaccinations seem to be the most useful intervention to increase the vaccination uptake in HCWs. However, our study suggests that better results in the vaccination uptake in HCWs were obtained by combining interventions in different areas. Educational campaigns alone could not have an impact on vaccination coverage. LTCFs represent an ideal setting to perform preventive multi-approach interventions for the epidemiological transition toward aging and chronicity.

Predictors for influenza vaccine acceptance among patients with inflammatory rheumatic diseases

BACKGROUND

Patients with inflammatory rheumatic diseases are at higher risk for influenza and current guidelines recommend vaccination for this group of patients. The aim of this study was to evaluate the vaccination coverage and predictors for influenza vaccination among patients with inflammatory rheumatic diseases.

METHODS

This survey was conducted at the outpatient rheumatology clinic at the Medical University of Vienna between July and October 2017. All patients diagnosed with an inflammatory rheumatic disease and receiving immunosuppressive therapy were asked to complete a questionnaire about their influenza vaccination status for 2016/17.

RESULTS

490 patients with rheumatic diseases completed a questionnaire (33% male, mean age 55.3 years). The influenza vaccination rate for the previous season was 25.3% (n = 124/490). Predictors for a positive influenza vaccination status were higher age (Adjusted Odds Ratio 5.0, 95% Confidence Interval 2.4-10.4) and treatment with biological disease-modifying antirheumatic drugs (AOR 2.0, 95% CI 1.3-3.1). Patients who received a recommendation for influenza vaccination by their general practitioner were significantly more likely to be vaccinated than those who did not (57% vs. 15%, AOR 6.6, 95% CI 4.1-10.8); even more so if they received a recommendation by their rheumatologist (62% vs. 19%, AOR 9.0, 95% CI 4.9-16.5). The main reasons for patients to decline influenza vaccination were fear of side effects (36%), concerns that vaccination might not be effective due to their immunosuppressed condition (38%) or that it might worsen the rheumatic disease (20%).

CONCLUSIONS

A moderate influenza vaccination rate of 25.3% was detected among patients with inflammatory rheumatic diseases. Recommendation of the influenza vaccine by a physician exerts the most effective impact on a positive vaccination status.

Influenza-associated mortality determined from all-cause mortality, Denmark 2010/11-2016/17: The FluMOMO model

Background

In temperate zones, all‐cause mortality exhibits a marked seasonality, and influenza represents a major cause of winter excess mortality. We present a statistical model, FluMOMO, which estimate influenza‐associated mortality from all‐cause mortality data and apply it to Danish data from 2010/11 to 2016/17.

Methods

We applied a multivariable time series model with all‐cause mortality as outcome, influenza activity and extreme temperatures as explanatory variables while adjusting for time trend and seasonality. Three indicators of weekly influenza activity (IA) were explored: percentage of consultations for influenza‐like illness (ILI) at primary health care, national percentage of influenza‐positive samples, and the product of ILI percentage and percentage of influenza‐positive specimens in a given week, that is, the Goldstein index.

Results

Independent of the choice of parameter to represent influenza activity, the estimated influenza‐associated mortality showed similar patterns with the Goldstein index being the most conservative. Over the 7 winter seasons, the median influenza‐associated mortality per 100 000 population was 17.6 (range: 0.0‐36.8), 14.1 (0.3‐31.6) and 8.3 (0.0‐25.0) for the 3 indicators, respectively, for all ages.

Conclusion

The FluMOMO model fitted the Danish data well and has the potential to estimate all‐cause influenza‐associated mortality in near real time and could be used as a standardised method in other countries. We recommend using the Goldstein index as the influenza activity indicator in the FluMOMO model. Further work is needed to improve the interpretation of the estimated effects.

Estimates of global seasonal influenza-associated respiratory mortality: a modelling study

BACKGROUND

Estimates of influenza-associated mortality are important for national and international decision making on public health priorities. Previous estimates of 250 000-500 000 annual influenza deaths are outdated. We updated the estimated number of global annual influenza-associated respiratory deaths using country-specific influenza-associated excess respiratory mortality estimates from 1999-2015.

METHODS

We estimated country-specific influenza-associated respiratory excess mortality rates (EMR) for 33 countries using time series log-linear regression models with vital death records and influenza surveillance data. To extrapolate estimates to countries without data, we divided countries into three analytic divisions for three age groups (<65 years, 65-74 years, and ≥75 years) using WHO Global Health Estimate (GHE) respiratory infection mortality rates. We calculated mortality rate ratios (MRR) to account for differences in risk of influenza death across countries by comparing GHE respiratory infection mortality rates from countries without EMR estimates with those with estimates. To calculate death estimates for individual countries within each age-specific analytic division, we multiplied randomly selected mean annual EMRs by the country's MRR and population. Global 95% credible interval (CrI) estimates were obtained from the posterior distribution of the sum of country-specific estimates to represent the range of possible influenza-associated deaths in a season or year. We calculated influenza-associated deaths for children younger than 5 years for 92 countries with high rates of mortality due to respiratory infection using the same methods.

FINDINGS

EMR-contributing countries represented 57% of the global population. The estimated mean annual influenza-associated respiratory EMR ranged from 0·1 to 6·4 per 100 000 individuals for people younger than 65 years, 2·9 to 44·0 per 100 000 individuals for people aged between 65 and 74 years, and 17·9 to 223·5 per 100 000 for people older than 75 years. We estimated that 291 243-645 832 seasonal influenza-associated respiratory deaths (4·0-8·8 per 100 000 individuals) occur annually. The highest mortality rates were estimated in sub-Saharan Africa (2·8-16·5 per 100 000 individuals), southeast Asia (3·5-9·2 per 100 000 individuals), and among people aged 75 years or older (51·3-99·4 per 100 000 individuals). For 92 countries, we estimated that among children younger than 5 years, 9243-105 690 influenza-associated respiratory deaths occur annually.

INTERPRETATION

These global influenza-associated respiratory mortality estimates are higher than previously reported, suggesting that previous estimates might have underestimated disease burden. The contribution of non-respiratory causes of death to global influenza-associated mortality should be investigated.

FUNDING

None.

[Immunizing is not only a children's matter! : Why vaccinations are also important for adults]

Vaccinations belong to the ten most effective public health achievements worldwide. While immunization programms for children are installed in Europe, vaccinations for adults are not established. However, adult vaccination is extremely meaningful: increasing age means a higher susceptibility to infectious diseases, health problems and multimorbidity will increase. The burden of vaccine-preventable diseases is still high in Europe. Due to immunosenescence (older) adults are less protected against pathogens, antibody titers after vaccinations are lower and immunity lasts shorter. There is striking lack of data of adult vaccination rates and an international consensus regarding adult vaccination recommendations or guidelines are not available in Europe. In only six countries a comprehensive document describing recommended vaccinations for adults is available, among them Austria. The awareness of the importance of adult vaccination over the whole lifetime is not present to the necessary extent in Europe and has to be promoted.

Predictors for and coverage of influenza vaccination among HIV-positive patients: a cross-sectional survey

OBJECTIVES

Influenza vaccination is recommended for HIV-infected patients, but limited data about vaccination rates are available. The aim of this study was to evaluate the coverage of and predictors for influenza vaccination among HIV-positive patients.

METHODS

All HIV-positive patients who visited the HIV out-patient department of the University Hospital of Vienna, Austria, between June and August 2015 were asked to participate in this survey by completing a questionnaire.

RESULTS

A total of 455 HIV-positive patients completed a questionnaire, with 359 male and 96 female participants with a mean age of 46 years. The influenza vaccination rate for the previous season (2014/2015) was 11.9% [n = 54/455; 95% confidence interval (CI) 9.2-15.2%]. Older age was significantly associated with a positive influenza vaccination status. Obtaining information through a medical consultation or receiving a direct recommendation for vaccination by a physician had a significant impact on vaccination behaviour. The probability of being vaccinated against influenza was about 13 times higher among patients who received a recommendation for vaccination by their family physician or by their HIV specialist (P < 0.001). Important reasons for declining vaccination were fear of side effects (39%), not considering influenza as a severe disease (36%) and reasons related to HIV: 17% were worried that the vaccine could worsen the course of HIV infection and 16% believed vaccination would fail because of their compromised immune system.

CONCLUSIONS

A low influenza vaccination rate of 11.9% was detected in this HIV-positive cohort. The most effective impact for a positive vaccination status was direct recommendation of the influenza vaccine by the attending physician.

A comprehensive review of the epidemiology and disease burden of Influenza B in 9 European countries

This review was undertaken to consolidate information on the epidemiology and burden of influenza B, as well as the circulation patterns of influenza B lineage in 9 European countries. Following a comprehensive search of peer-reviewed and gray literature sources, we found that published data on influenza B epidemiology and burden are scarce. Surveillance data show frequent co-circulation of both influenza B lineages during influenza seasons, but little is known about its impact, especially in adults and the clinical burden of influenza B remains unknown. Mismatch between the circulating influenza B lineage and vaccine recommendations has been seen in at least one influenza season in every country. Such observations could impact the effectiveness of seasonal influenza vaccination programs using trivalent vaccines, which contain only one influenza B lineage (B/Yamagata or B/Victoria) and highlight the need for local studies to better understand the epidemiology and burden of influenza B in these countries.

Influenza-attributable deaths in south-eastern France (1999 to 2010): mortality predictions were undependable

Background

Following the 2009 influenza pandemic, several studies showed that the mortality pattern associated with the A(H1N1)2009 virus primarily affected children and young adults. In this study, we aimed to estimate the influenza-attributable deaths during the periods from 1999 to 2010, in the Provence-Alpes-Côte-d’Azur (PACA) region of south-eastern France in order to corroborate the hypothesis that (i) influenza-attributable deaths caused by A(H1N1)2009 strain were much lower than initially expected.

Methods

In order to compare our results with published data, we used the same statistical model of an Austrian team, using a Poisson model adjusted on co-circulating respiratory syncytial virus to explain the weekly mortality.

Results

We assessed that 5.7 % of the respiratory deaths were attributable to influenza virus during the 2009–2010 pandemic season. This mortality was lower than that observed during the ten preceding epidemic periods (13.8 % on average). Age group- based analysis revealed that during the pandemic period, the groups under 65 had a systematically higher excess of respiratory mortality while the age group over 65 had a much lower mortality than during the seasonal epidemic seasons. Similarly, among the less specific outcome (non violent and cardiovascular mortality) the age groups over 45 had higher excess of mortality during the seasonal epidemics than during the pandemic period.

Conclusions

Since most of the influenza mortality is commonly observed in the elderly group (>65 year-old), the moderate elderly mortality during the 2009 pandemic period has impacted the total mortality, and has resulted in a reduced total mortality despite an increased mortality in the young age group. Despite using identical parameters and the same approach as in a previously published study using an Austrian population sample, we observed a lower excess respiratory mortality in the south-eastern France than in Vienna. Thus, the pandemic virus caused less death than the epidemic viruses that circulated during the preceding years. In contrast with catastrophic predictions made in the early phase of the pandemic, human lives were saved during the circulation period of A(H1N1)2009 virus, resulting in a lower overall mortality.

Are influenza-associated morbidity and mortality estimates for those ≥ 65 in statistical databases accurate, and an appropriate test of influenza vaccine effectiveness?

PURPOSES

To assess the accuracy of estimates using statistical databases of influenza-associated morbidity and mortality, and precisely measure influenza vaccine effectiveness.

PRINCIPAL RESULTS

Laboratory testing of influenza is incomplete. Death certificates under-report influenza. Statistical database models are used as an alternative to randomised controlled trials (RCTs) to assess influenza vaccine effectiveness. Evidence of the accuracy of influenza morbidity and mortality estimates was sought from: (1) Studies comparing statistical models. For four studies Poisson and ARIMA models produced higher estimates than Serfling, and Serfling higher than GLM. Which model is more accurate is unknown. (2) Studies controlling confounders. Fourteen studies mostly controlled one confounder (one controlled comorbidities), and limited control of confounders limits accuracy.

EVIDENCE FOR VACCINE EFFECTIVENESS WAS SOUGHT FROM

(1) Studies of regions with increasing vaccination rates. Of five studies two controlled for confounders and one found a positive vaccination effect. Three studies did not control confounders and two found no effect of vaccination. (2) Studies controlling multiple confounders. Of thirteen studies only two found a positive vaccine effect and no mortality differences between vaccinees and non-vaccinees in non-influenza seasons, showing confounders were controlled. Key problems are insufficient testing for influenza, using influenza-like illness, heterogeneity of seasonal and pandemic influenza, population aging, and incomplete confounder control (co-morbidities, frailty, vaccination history) and failure to demonstrate control of confounders by proving no mortality differences between vaccinees and non-vaccinees in non-influenza seasons.

MAJOR CONCLUSIONS

Improving model accuracy requires proof of no mortality differences in pre-influenza periods between the vaccinated and non-vaccinated groups, and reduction in influenza morbidity and mortality in seasons with a good vaccine match, more virulent strains, in the younger elderly with less immune senescence, and specific outcomes (laboratory-confirmed outcomes, pneumonia deaths). Proving influenza vaccine effectiveness requires appropriately powered RCTs, testing participants with RT-PCR tests, and comprehensively monitoring morbidity and mortality.

A robust parameter estimation method for estimating disease burden of respiratory viruses

BACKGROUND

Poisson model has been widely applied to estimate the disease burden of influenza, but there has been little success in providing reliable estimates for other respiratory viruses.

METHODS

We compared the estimates of excess hospitalization rates derived from the Poisson models with different combinations of inference methods and virus proxies respectively, with the aim to determine the optimal modeling approach. These models were validated by comparing the estimates of excess hospitalization attributable to respiratory viruses with the observed rates of laboratory confirmed paediatric hospitalization for acute respiratory infections obtained from a population based study.

RESULTS

The Bayesian inference method generally outperformed the classical likelihood estimation, particularly for RSV and parainfluenza, in terms of providing estimates closer to the observed hospitalization rates. Compared to the other proxy variables, age-specific positive counts provided better estimates for influenza, RSV and parainfluenza, regardless of inference methods. The Bayesian inference combined with age-specific positive counts also provided valid and reliable estimates for excess hospitalization associated with multiple respiratory viruses in both the 2009 H1N1 pandemic and interpandemic period.

CONCLUSIONS

Poisson models using the Bayesian inference method and virus proxies of age-specific positive counts should be considered in disease burden studies on multiple respiratory viruses.

Distinct differences in clinical manifestation and viral laboratory parameters between children and adults with influenza A(H1N1)pdm09 infection--a retrospective comparative analysis

During the influenza pandemic 2009 children and adults differed in the clinical course of the influenza disease. In following the question arose, if the case definitions used within the national and international organizations are an adequate tool for the clinical diagnosis of influenza in children as well as in adults. Therefore medical charts from 146 children and 229 adults were retrospectively analyzed. In addition, the initial viral loads of all 375 patients and the duration of virus shedding of a subset of 79 patients were also investigated. Children show a wider clinical spectrum including gastro enteric symptoms and also a different spectrum of laboratory parameters like elevated CRP-levels, leucocytosis, and higher viral loads. Further, children show significantly more often complications, for example, myositis that may be underdiagnosed. In patients receiving antiviral-therapy complications occurred significantly less often and the presence of symptoms was significantly shorter compared to the untreated group (2.3 days vs. 6.0 days). In summary, the differences in the clinical picture between children and adults should be taken into consideration for the clinical diagnosis of influenza and also for a future discussion on age specific influenza case definitions.

Mortality attributable to influenza in England and Wales prior to, during and after the 2009 pandemic

Very different influenza seasons have been observed from 2008/09-2011/12 in England and Wales, with the reported burden varying overall and by age group. The objective of this study was to estimate the impact of influenza on all-cause and cause-specific mortality during this period. Age-specific generalised linear regression models fitted with an identity link were developed, modelling weekly influenza activity through multiplying clinical influenza-like illness consultation rates with proportion of samples positive for influenza A or B. To adjust for confounding factors, a similar activity indicator was calculated for Respiratory Syncytial Virus. Extreme temperature and seasonal trend were controlled for. Following a severe influenza season in 2008/09 in 65+yr olds (estimated excess of 13,058 influenza A all-cause deaths), attributed all-cause mortality was not significant during the 2009 pandemic in this age group and comparatively low levels of influenza A mortality were seen in post-pandemic seasons. The age shift of the burden of seasonal influenza from the elderly to young adults during the pandemic continued into 2010/11; a comparatively larger impact was seen with the same circulating A(H1N1)pdm09 strain, with the burden of influenza A all-cause excess mortality in 15-64 yr olds the largest reported during 2008/09-2011/12 (436 deaths in 15-44 yr olds and 1,274 in 45-64 yr olds). On average, 76% of seasonal influenza A all-age attributable deaths had a cardiovascular or respiratory cause recorded (average of 5,849 influenza A deaths per season), with nearly a quarter reported for other causes (average of 1,770 influenza A deaths per season), highlighting the importance of all-cause as well as cause-specific estimates. No significant influenza B attributable mortality was detected by season, cause or age group. This analysis forms part of the preparatory work to establish a routine mortality monitoring system ahead of introduction of the UK universal childhood seasonal influenza vaccination programme in 2013/14.

The Rotterdam Study: 2014 objectives and design update

The Rotterdam Study is a prospective cohort study ongoing since 1990 in the city of Rotterdam in The Netherlands. The study targets cardiovascular, endocrine, hepatic, neurological, ophthalmic, psychiatric, dermatological, oncological, and respiratory diseases. As of 2008, 14,926 subjects aged 45 years or over comprise the Rotterdam Study cohort. The findings of the Rotterdam Study have been presented in over a 1,000 research articles and reports (see www.erasmus-epidemiology.nl/rotterdamstudy ). This article gives the rationale of the study and its design. It also presents a summary of the major findings and an update of the objectives and methods.

[Vaccination recommendations for health care workers in Austria]

In Austria the vaccination coverage among health care workers (HCW) - particularly among hospital personnel - is not sufficient. This is of specific concern, because not only the individual protection but also the prevention of disease transmission of vaccine preventable diseases between HCW and patients needs to be guaranteed. Particularly immunosuppressed patients, who are at higher risk for morbidity and mortality due to certain infections, but cannot be vaccination themselves, must be able to rely on herd protection, i.e. not being infected by surrounding/caring persons. The following publication provides for the first time detailed guidelines for vaccination programs for HCWs in Austria, including personnel within hospitals, medical institutions and laboratories, as well as Medical Universities including students. Moreover, these guidelines are also recommended to medical personnel in outpatient clinics, social service institutions and medical practices. Additionally to the vaccination schedules this publication also includes a chapter on ethical as well as legal background underlying these recommendations.

Years of life lost in the first wave of the 2009 influenza A(H1N1) pandemic in Hong Kong

The impact of influenza pandemics might be overestimated; the published studies of years of life lost (YLL) have typically ignored the presence of underlying chronic conditions or health risk behaviors in most deaths. We used data on deaths involving laboratory-confirmed 2009 influenza A(H1N1) virus infection that occurred between April 2009 and May 2010 in Hong Kong, China, to adjust for these underlying risk factors. Life expectancy was corrected with hazard-based modifications to the life tables. The excess hazards posed by underlying risk factors were added to the "baseline" age-specific hazards in the local life tables to reflect the life expectancy associated with each underlying risk factor. Of 72 deceased persons with laboratory-confirmed 2009 influenza A(H1N1) virus infection, 56% had underlying risk factors. We estimated that the 2009 pandemic was associated with 1,540 (95% confidence interval: 1,350, 1,630) YLL after adjustment for age and underlying risk factors. This figure is approximately 25% lower than the YLL estimate of 2,080 derived after adjustment for age but not for risk factors. Our analysis demonstrates the potential scale of bias in YLL estimation if underlying risk factors are ignored. The estimation of YLL with correction for underlying risk factors in addition to age could also provide a framework for similar calculations elsewhere.

Mortality associated with influenza in tropics, state of são paulo, Brazil, from 2002 to 2011: the pre-pandemic, pandemic, and post-pandemic periods

The impact of the seasonal influenza and 2009 AH1N1 pandemic influenza on mortality is not yet completely understood, particularly in tropical and subtropical countries. The trends of influenza related mortality rate in different age groups and different outcomes on a area in tropical and subtropical climate with more than 41 million people (State of São Paulo, Brazil), were studied from 2002 to 2011 were studied. Serfling-type regression analysis was performed using weekly mortality registries and virological data obtained from sentinel surveillance. The prepandemic years presented a well-defined seasonality during winter and a clear relationship between activity of AH3N2 and increase of mortality in all ages, especially in individuals older than 60 years. The mortality due to pneumonia and influenza and respiratory causes associated with 2009 pandemic influenza in the age groups 0–4 years and older than 60 was lower than the previous years. Among people aged 5–19 and 20–59 years the mortality was 2.6 and 4.4 times higher than that in previous periods, respectively. The mortality in all ages was higher than the average of the previous years but was equal mortality in epidemics of AH3N2. The 2009 pandemic influenza mortality showed significant differences compared to other years, especially considering the age groups most affected.

Excess mortality associated with influenza A and B virus in Hong Kong, 1998-2009

BACKGROUND

Although deaths associated with laboratory-confirmed influenza virus infections are rare, the excess mortality burden of influenza estimated from statistical models may more reliably quantify the impact of influenza in a population.

METHODS

We applied age-specific multiple linear regression models to all-cause and cause-specific mortality rates in Hong Kong from 1998 through 2009. The differences between estimated mortality rates in the presence or absence of recorded influenza activity were used to estimate influenza-associated excess mortality.

RESULTS

The annual influenza-associated all-cause excess mortality rate was 11.1 (95% confidence interval [CI], 7.2-14.6) per 100,000 person-years. We estimated an average of 751 (95% CI, 488-990) excess deaths associated with influenza annually from 1998 through 2009, with 95% of the excess deaths occurring in persons aged ≥65 years. Most of the influenza-associated excess deaths were from respiratory (53%) and cardiovascular (18%) causes. Influenza A(H3N2) epidemics were associated with more excess deaths than influenza A(H1N1) or B during the study period.

CONCLUSIONS

Influenza was associated with a substantial number of excess deaths each year, mainly among the elderly, in Hong Kong in the past decade. The influenza-associated excess mortality rates were generally similar in Hong Kong and the United States.