Further evidence for bias in observational studies of influenza vaccine effectiveness: the 2009 influenza A(H1N1) pandemic

Effectiveness of influenza vaccination on hospitalization outcomes among older patients with diabetes

OBJECTIVE

In older populations admitted for diabetes, limited evidence suggests that influenza vaccination protects against hospitalization outcomes.

METHODS

This study pooled 27,620 hospitalizations recorded for elderly diabetes patients from the Beijing Elderly Influenza Vaccination Information Registration Database (2013-2018) and the Beijing Urban Employee Basic Medical Insurance Database (2013-2018). Generalized linear regression and propensity score matching were conducted to estimate the effects of influenza vaccination on hospitalization outcomes (in-hospital all-cause mortality, readmission, length and costs of hospitalization), adjusting for measurable confounding factors. The low influenza period (May-July) was used as a reference period to adjust for unmeasured confounding factors during the peak influenza period (November-January).

RESULTS

In propensity score matching, influenza vaccination in peak influenza period could reduce the risk of in-hospital death (OR: 0.47[0.22,0.97]) and readmission (OR: 0.70[0.60,0.81]), length of hospitalization (β: -1.32[-1.47, -1.17]) and medical costs (GMR: 0.90[0.88,0.92]). After adjusting for unmeasured confounding factors, influenza vaccination was associated with 17% (ratio of ORs: 0.83 [0.69, 1.02]) lower risk of readmission and shorter length of hospitalization (difference in β: -0.23 [-0.62, 0.16]). The subgroup analyses showed that male patients with older age and poorer health conditions could benefit more after influenza vaccination.

CONCLUSION

Influenza vaccination could significantly improve hospitalization outcomes in elderly diabetic patients. This provides evidence supporting free influenza vaccination policies for vulnerable populations in low- and middle-income countries.

Confounding and Negative Control Methods in Observational Study of SARS-CoV-2 Vaccine Effectiveness: A Nationwide, Population-Based Danish Health Registry Study

Background

Observational studies of SARS-CoV-2 vaccine effectiveness are prone to confounding, which can be illustrated using negative control methods.

Methods

Nationwide population-based cohort study including two cohorts of Danish residents 60-90 years of age matched 1:1 on age and sex: A vaccinated and a non-vaccinated cohort, including 61052 SARS-CoV-2 vaccinated individuals between 1 March and 1 July 2021 and 61052 individuals not vaccinated preceding 1 July 2021. From these two cohorts, we constructed negative control cohorts of individuals diagnosed with SARS-CoV-2 infection or acute myocardial infarction, stroke, cancer, low energy fracture, or head-trauma. Outcomes were SARS-CoV-2 infection, negative control outcomes (eg, mammography, prostate biopsy, operation for cataract, malignant melanoma, examination of eye and ear), and death. We used Cox regression to calculate adjusted incidence and mortality rate ratios (aIRR and aMRR).

Results

Risks of SARS-CoV2 infection and all negative control outcomes were elevated in the vaccinated population, ranging from an aIRR of 1.15 (95% CI: 1.09-1.21) for eye examinations to 3.05 (95% CI: 2.24-4.14) for malignant melanoma. Conversely, the risk of death in the SARS-CoV-2 infected cohort and in all negative control cohorts was lower in vaccinated individuals, ranging from an aMRR of 0.23 (95% CI: 0.19-0.26) after SARS-CoV-2 infection to 0.50 (95% CI: 0.37-0.67) after stroke.

Conclusion

Our findings indicate that observational studies of SARS-CoV-2 vaccine effectiveness may be subject to substantial confounding. Therefore, randomized trials are essential to establish vaccine efficacy after the emergence of new SARS-CoV-2 variants and the rollout of multiple booster vaccines.

The impact of EV71 vaccination program on hand, foot and mouth disease in Zhejiang Province, China: A negative control study

Objective

To estimate the potential causal impact of Enterovirus A71 (EV71) vaccination program on the reduction of EV71-infected hand, foot, and mouth disease (HFMD) in Zhejiang Province.

Methods

We utilized the longitudinal surveillance dataset of HFMD and EV71 vaccination in Zhejiang Province during 2010-2019. We estimated vaccine efficacy using a Bayesian structured time series (BSTS) model, and employed a negative control outcome (NCO) model to detect unmeasured confounding and reveal potential causal association.

Results

We estimated that 20,132 EV71 cases (95% CI: 16,733, 23,532) were prevented by vaccination program during 2017-2019, corresponding to a reduction of 29% (95% CI: 24%, 34%). The effectiveness of vaccination increased annually, with reductions of 11% (95% CI: 6%, 16%) in 2017 and 66% (95% CI: 61%, 71%) in 2019. Children under 5 years old obtained greater benefits compared to those over 5 years. Cities with higher vaccination coverage experienced a sharper EV71 reduction compared to those with lower coverage. The NCO model detected no confounding factors in the association between vaccination and EV71 cases reduction.

Conclusions

This study suggested a potential causal effect of the EV71 vaccination, highlighting the importance of achieving higher vaccine coverage to control the HFMD.

Covid-19 vaccination programme effectiveness against SARS-CoV-2 related infections, hospital admissions and deaths in the Apulia region of Italy: a one-year retrospective cohort study

Studies reporting vaccine effectiveness against COVID-19 outcomes concentrate mainly on estimates of one single type of vaccine and variant, seldom considering waning effects. We aimed to estimate the effectiveness of the overall COVID-19 vaccination programme implemented in the Apulia region of Italy at preventing SARS-CoV-2 infections, COVID-19-related hospital admissions and deaths during alpha and delta variant dominant periods. We conducted a retrospective cohort study using electronic health records of persons 16 years and older resident in the Apulia region, assessing the effectiveness of the combined use of BNT162b2, mRNA-1273, ChAdOx1-S and Ad26.COV2.S vaccines against confirmed COVID-19 infections, hospitalisations and deaths, for fully and partially vaccinated persons as well as by time since vaccination and variants. Cox regression models yielding hazard ratios were used to calculate the overall vaccination programme effectiveness. From 1 January to 1 December 2021, we included 3,530,967 eligible persons in the cohort, of whom 2,770,299 were fully vaccinated and 158,313 were COVID-19 positive at the end of the study period. The effectiveness of the programme over the entire study period for fully vaccinated persons against COVID-19 infection, hospitalisation and death were 87.69% (CI95% 87.73-88.18), 94.08% (93.58-94.54) and 95.95% (CI95% 95.26-96.54), respectively. The effectiveness against COVID-19 infection of fully vaccinated subjects during the alpha and delta period was respectively 88.20% (CI95% 87.60-99.78) and 59.31% (CI95% 57.91-60.67), against hospitalisation 93.89% (CI95% 92.67-94.90) and 88.32% (CI95% 86.50-89.90) and against death 93.83% (CI95% 91.65-95.45) and 85.91 (CI95% 79.98-90.09). The waning effects of the programme regarding COVID-19 infection during the delta period were stronger than for alpha, with 75.85% (CI95% 74.38-77.24) effectiveness after 1-2 months and 8.35% (CI95% 3.45-13.01) after 5-6 months after full vaccination. The effectiveness against hospitalisation and death during the delta period waned rapidly and at 7-8-months after the full vaccination respectively decreased to 27.67% (CI95% 7.48-43.45) and 48.47 (CI95% 53.97-34.82). Our study suggests that the COVID-19 vaccination program in Apulia was strongly protective against COVID-19 infection, hospitalisation, and death due to alpha as well as delta variants, although its effectiveness is reduced over time.

Effects of Influenza Vaccination in Patients with Interstitial Lung Diseases: An Epidemiological Claims Data Analysis

Rationale

Vaccination is the most effective protection against influenza. Patients with interstitial lung diseases (ILDs) represent a high-risk group for influenza complications. Thus, yearly influenza vaccination is recommended, but evidence on its effects is sparse.

Objectives

This study aimed to compare all-cause mortality and all-cause and respiratory-related hospitalization between vaccinated and unvaccinated patients with ILD.

Methods

Using data from the largest German statutory health insurance fund (about 27 million insurees in 2020), we analyzed four influenza seasons from 2014–2015 to 2017–2018 and compared vaccinated with unvaccinated patients with ILD. Starting from September 1 of each year, we matched vaccinated and unvaccinated patients in a 1:1 ratio using a rolling cohort design. Mortality and hospitalization were compared with Kaplan-Meier plots, and effects were calculated during the influenza season (in season) with risk ratios.

Results

Both the vaccinated and the unvaccinated cohorts included 7,503 patients in 2014–2015, 10,318 in 2015–2016, 12,723 in 2016–2017, and 13,927 in 2017–2018. Vaccination rates were low at 43.2% in season 2014–2015 and decreased over time to 39.9% in season 2017–2018. The risk ratios for all-cause mortality were 0.79 (95% confidence interval [CI], 0.65–0.97; P = 0.02) in season 2014–2015, 0.66 (95% CI, 0.54–0.80; P < 0.001) in 2015–2016, 0.89 (95% CI, 0.76–1.04; P = 0.15) in 2016–2017, and 0.95 (95% CI, 0.81–1.12; P = 0.57) in 2017–2018. The effects on all-cause hospitalization and respiratory-related hospitalization were similar in all seasons.

Conclusions

Although an unequivocally beneficial impact of influenza vaccination in patients with ILD could not be demonstrated, we observed promising results regarding avoidance of all-cause mortality in half of the seasons observed. Given the low vaccination rates, further efforts are necessary to improve vaccination rates in patients with ILD.

Identifying and managing ADRs: Qualitative analysis of patient reports to the UK Yellow Card Scheme

INTRODUCTION

Adverse drug reactions (ADRs) can have significant negative impact on peoples' daily lives, with physical, economic, social and/or psychological effects. Patient reporting of ADRs has been facilitated by pharmacovigilance systems across Europe. However, capturing data on patients' experiences of ADRs has proved challenging. Existing patient reports to the UK Yellow Card Scheme (YCS) contain free text comments which could be useful sources of information.

OBJECTIVES

To investigate patients' experiences of ADRs and their impact on patients as described in free-text data within patient Yellow Card (YC) reports submitted to the Medicines and Healthcare products Regulatory Agency (MHRA).

METHODS

A qualitative review of narrative texts was conducted on free text data from 2255 patient YC reports - July to December 2015.

RESULTS

Three key narrative themes emerged from analysis of the free text data in 2255 reports: (1) identification of ADRs, (2) severity and impact of ADRs and (3) management of ADRs. Temporal associations were the most common method of identification followed by differential diagnoses and confirmation with information sources such as healthcare professionals (HCPs). A combination of explicit and implicit impacts were described - physical, psychological, economic and social effects often persisted and caused serious disruption to many patients' lives. A range of strategies were used to manage ADRs including consultation with HCPs, stopping/reducing the medicine or taking medicines to alleviate symptoms.

CONCLUSION

Free text data from YC reports has been an underutilised resource to date, however this research has confirmed its potential value to pharmacovigilance and medication safety research.

Impact and effectiveness of mRNA BNT162b2 vaccine against SARS-CoV-2 infections and COVID-19 cases, hospitalisations, and deaths following a nationwide vaccination campaign in Israel: an observational study using national surveillance data

BACKGROUND

Following the emergency use authorisation of the Pfizer-BioNTech mRNA COVID-19 vaccine BNT162b2 (international non-proprietary name tozinameran) in Israel, the Ministry of Health (MoH) launched a campaign to immunise the 6·5 million residents of Israel aged 16 years and older. We estimated the real-world effectiveness of two doses of BNT162b2 against a range of SARS-CoV-2 outcomes and to evaluate the nationwide public-health impact following the widespread introduction of the vaccine.

METHODS

We used national surveillance data from the first 4 months of the nationwide vaccination campaign to ascertain incident cases of laboratory-confirmed SARS-CoV-2 infections and outcomes, as well as vaccine uptake in residents of Israel aged 16 years and older. Vaccine effectiveness against SARS-CoV-2 outcomes (asymptomatic infection, symptomatic infection, and COVID-19-related hospitalisation, severe or critical hospitalisation, and death) was calculated on the basis of incidence rates in fully vaccinated individuals (defined as those for whom 7 days had passed since receiving the second dose of vaccine) compared with rates in unvaccinated individuals (who had not received any doses of the vaccine), with use of a negative binomial regression model adjusted for age group (16-24, 25-34, 35-44, 45-54, 55-64, 65-74, 75-84, and ≥85 years), sex, and calendar week. The proportion of spike gene target failures on PCR test among a nationwide convenience-sample of SARS-CoV-2-positive specimens was used to estimate the prevelance of the B.1.1.7 variant.

FINDINGS

During the analysis period (Jan 24 to April 3, 2021), there were 232 268 SARS-CoV-2 infections, 7694 COVID-19 hospitalisations, 4481 severe or critical COVID-19 hospitalisations, and 1113 COVID-19 deaths in people aged 16 years or older. By April 3, 2021, 4 714 932 (72·1%) of 6 538 911 people aged 16 years and older were fully vaccinated with two doses of BNT162b2. Adjusted estimates of vaccine effectiveness at 7 days or longer after the second dose were 95·3% (95% CI 94·9-95·7; incidence rate 91·5 per 100 000 person-days in unvaccinated vs 3·1 per 100 000 person-days in fully vaccinated individuals) against SARS-CoV-2 infection, 91·5% (90·7-92·2; 40·9 vs 1·8 per 100 000 person-days) against asymptomatic SARS-CoV-2 infection, 97·0% (96·7-97·2; 32·5 vs 0·8 per 100 000 person-days) against symptomatic COVID-19, 97·2% (96·8-97·5; 4·6 vs 0·3 per 100 000 person-days) against COVID-19-related hospitalisation, 97·5% (97·1-97·8; 2·7 vs 0·2 per 100 000 person-days) against severe or critical COVID-19-related hospitalisation, and 96·7% (96·0-97·3; 0·6 vs 0·1 per 100 000 person-days) against COVID-19-related death. In all age groups, as vaccine coverage increased, the incidence of SARS-CoV-2 outcomes declined. 8006 of 8472 samples tested showed a spike gene target failure, giving an estimated prevalence of the B.1.1.7 variant of 94·5% among SARS-CoV-2 infections.

INTERPRETATION

Two doses of BNT162b2 are highly effective across all age groups (≥16 years, including older adults aged ≥85 years) in preventing symptomatic and asymptomatic SARS-CoV-2 infections and COVID-19-related hospitalisations, severe disease, and death, including those caused by the B.1.1.7 SARS-CoV-2 variant. There were marked and sustained declines in SARS-CoV-2 incidence corresponding to increasing vaccine coverage. These findings suggest that COVID-19 vaccination can help to control the pandemic.

FUNDING

None.

Infections causing stroke or stroke-like syndromes

BACKGROUND

Stroke has relevant morbidity and mortality despite appropriate treatments and early diagnosis. Beside common risk factors such as diabetes and atrial fibrillation, infections can be involved in stroke pathogenesis, probably causing a systemic release of cytokines and other inflammatory mediators, triggering a latent pro-thrombotic state or damaging the vascular endothelium. In other cases, infections can occur as stroke-like syndromes, requiring a high grade of suspicion to avoid a delay in establishing a correct diagnosis.

RESULTS

Treatment of stroke or stroke-like syndromes of infectious origin can be difficult. When a previous infective event triggers stroke, Alteplase administration can be associated with a higher incidence of bleeding and the extension of the ischaemic area can be major than expected. On the other hand, when stroke is part of some infectious diseases' presentation as in endocarditis, bacterial or tuberculous meningitis and meningo-vascular syphilis, a correct diagnosis can be difficult. The management of these stroke-like syndromes is not standardised because common treatments proven to be effective for patients with stroke of vascular origin can worsen the prognosis, as it can be demonstrated after to be incorrect Alteplase administration to patients with endocarditis with septic embolism to the brain is associated with an increase of the risk of haemorrhage.

CONCLUSIONS

Stroke or stroke-like syndrome of infectious origin can be observed in an important proportion of case presenting with sensory-motor deficit of unknown origin; their accurate diagnosis has a considerable impact in terms of treatment choices and outcome.

Higher frequency of hospitalization but lower relative mortality for pandemic influenza in people with type 2 diabetes

BACKGROUND

There is limited evidence linking type 2 diabetes (T2D) to influenza-related complications.

OBJECTIVES

To test a set of research questions relating to pandemic influenza vaccination, hospitalization and mortality in people with and without T2D.

METHODS

In this population-based cohort study, we linked individual-level data from several national registers for all Norwegian residents aged 30 years or more as of January 2009. People with or without T2D at baseline (n = 2 992 228) were followed until December 2013. We used Cox regression to estimate adjusted hazard ratios (aHRs).

RESULTS

Pandemic influenza hospitalization was more common in individuals with T2D (aHR = 2.46, 95% CI 2.04-2.98). The mortality hazard ratio associated with hospitalization for pandemic influenza was lower in people with T2D (aHR = 1.82, 95% CI 1.21-2.74) than in those without T2D (aHR = 3.89, 95% CI 3.27-4.62). The same pattern was observed when restricting to 90-day mortality (aHR = 3.89, 95% CI 1.25-12.06 amongst those with T2D and aHR = 10.79, 95% CI 7.23-16.10 amongst those without T2D). The rate of hospitalization for pandemic influenza was 78% lower in those vaccinated compared to nonvaccinated amongst people with T2D (aHR = 0.22, 95% CI 0.11-0.39), whilst the corresponding estimate for those without T2D was 59% lower (aHR = 0.41, 95% CI 0.33-0.52). Mortality was 25% lower in those vaccinated compared to nonvaccinated amongst people with T2D (aHR = 0.75, 95% CI 0.73-0.77), whilst the corresponding estimate for those without T2D was 9% (aHR = 0.91, 95% CI 0.90-0.92).

CONCLUSIONS

There may have been a lower threshold for pandemic influenza hospitalization for people with T2D, rather than more severe influenza infection. Our combined results support the importance of influenza vaccination amongst people with T2D, especially during pandemics.

Comparative Effectiveness of High-Dose Versus Standard-Dose Influenza Vaccine Among Patients Receiving Maintenance Hemodialysis

RATIONALE & OBJECTIVE

Studies of patients on maintenance dialysis therapy suggest that standard-dose influenza vaccine (SDV) may not prevent influenza-related outcomes. Little is known about the comparative effectiveness of SDV versus high-dose influenza vaccine (HDV) in this population.

STUDY DESIGN

Cohort study using data from the US Renal Data System.

SETTING & PARTICIPANTS

507,552 adults undergoing in-center maintenance hemodialysis between the 2010 to 2011 and 2014 to 2015 influenza seasons.

EXPOSURES

SDV and HDV.

OUTCOMES

All-cause mortality, hospitalization due to influenza or pneumonia, and influenza-like illness during the influenza season.

ANALYTIC APPROACH

Patients were eligible for inclusion in multiple yearly cohorts; thus, our unit of analysis was the influenza patient-season. To examine the relationship between vaccine dose and effectiveness outcomes, we estimated risk differences and risk ratios using propensity score weighting of Kaplan-Meier functions, accounting for a wide range of patient- and facility-level characteristics. For nonmortality outcomes, we used competing-risk methods to account for the high mortality rate in the dialysis population.

RESULTS

Within 225,215 influenza patient-seasons among adults 65 years and older, 97.4% received SDV and 2.6% received HDV. We observed similar risk estimates for HDV and SDV recipients for mortality (risk difference, -0.08%; 95% CI, -0.85% to 0.80%), hospitalization due to influenza or pneumonia (risk difference, 0.15%; 95% CI, -0.69% to 0.93%), and influenza-like illness (risk difference, 0.00%; 95% CI, -1.50% to 1.08%). Our findings were similar among adults younger than 65 years, as well as within other subgroups defined by influenza season, age group, dialysis vintage, month of influenza vaccination, and vaccine valence.

LIMITATIONS

Residual confounding and outcome misclassification.

CONCLUSIONS

The HDV does not appear to provide additional protection beyond the SDV against all-cause mortality or influenza-related outcomes for adults undergoing hemodialysis. The additional cost and side effects associated with HDV should be considered when offering this vaccine. Future studies of HDV and other influenza vaccine strategies are warranted.

Risk Of Urticaria In Geriatric Stroke Patients Who Received Influenza Vaccination: A Retrospective Cohort Study

Objective

Urticaria is a mast cell-related disease caused severe itching and the lifetime prevalence of urticaria is about 20% in general population. Our purpose is to evaluate risk of urticaria in geriatric stroke patients received influenza vaccination (IV).

Methods

In a cohort of 192,728 patients with newly diagnosed stroke aged over 65 years obtained from 23 million people in Taiwan’s National Health Insurance between 2000 and 2008, we identified 9890 stroke patients who received IV and 9890 propensity score-matched stroke patients who did not receive IV. Controlling for immortal time bias, both the IV and non-IV groups were followed for one year. Urticaria events were identified during the follow-up period. We calculated the adjusted rate ratios (RRs) and 95% confidence intervals (CIs) of the one-year risk of urticaria associated with IV.

Results

During the follow-up period of one year, stroke patients with IV had a significantly higher risk of urticaria compared with non-IV stroke patients (RR 1.81, 95% CI 1.47–2.23). An increased risk of urticaria in stroke patients with IV was noted in both sexes, patients 65–84 years of age, patients with comorbid medical conditions, and various time intervals of follow-up. Vaccinated stroke patients with hemorrhage (RR 4.00, 95% CI 1.76–9.10) and those who received intensive care (RR 5.14, 95% CI 2.32–11.4) had a very high risk of urticaria compared with those without IV.

Conclusion

Receiving IV may be associated with an increased risk of urticaria in stroke patients. We could not infer the causality from the current results because of this study’s limitations. Future investigations are needed to evaluate the possible mechanism underlying the association between IV and urticaria.

Restriction of Pharmacoepidemiologic Cohorts to Initiators of Medications in Unrelated Preventive Drug Classes to Reduce Confounding by Frailty in Older Adults

Nonexperimental studies of the effectiveness of seasonal influenza vaccine in older adults have found 40%-60% reductions in all-cause mortality associated with vaccination, potentially due to confounding by frailty. We restricted our cohort to initiators of medications in preventive drug classes (statins, antiglaucoma drugs, and β blockers) as an approach to reducing confounding by frailty by excluding frail older adults who would not initiate use of these drugs. Using a random 20% sample of US Medicare beneficiaries, we framed our study as a series of nonrandomized "trials" comparing vaccinated beneficiaries with unvaccinated beneficiaries who had an outpatient health-care visit during the 5 influenza seasons occurring in 2010-2015. We pooled data across trials and used standardized-mortality-ratio-weighted Cox proportional hazards models to estimate the association between influenza vaccination and all-cause mortality before influenza season, expecting a null association. Weighted hazard ratios among preventive drug initiators were generally closer to the null than those in the nonrestricted cohort. Restriction of the study population to statin initiators with an uncensored approach resulted in a weighted hazard ratio of 1.00 (95% confidence interval: 0.84, 1.19), and several other hazard ratios were above 0.95. Restricting the cohort to initiators of medications in preventive drug classes can reduce confounding by frailty in this setting, but further work is required to determine the most appropriate criteria to use.

Challenges in estimating influenza vaccine effectiveness

Introduction: Influenza vaccination is regarded as the most effective way to prevent influenza infection. Due to the rapid genetic changes that influenza viruses undergo, seasonal influenza vaccines must be reformulated and re-administered annually necessitating the evaluation of influenza vaccine effectiveness (VE) each year. The estimation of influenza VE presents numerous challenges. Areas Covered: This review aims to identify, discuss, and, where possible, offer suggestions for dealing with the following challenges in estimating influenza VE: different outcomes of interest against which VE is estimated, study designs used to assess VE, sources of bias and confounding, repeat vaccination, waning immunity, population level effects of vaccination, and VE in at-risk populations. Expert Opinion: The estimation of influenza VE has improved with surveillance networks, better understanding of sources of bias and confounding, and the implementation of advanced statistical methods. Future research should focus on better estimates of the indirect effects of vaccination, the biological effects of vaccination, and how vaccines interact with the immune system. Specifically, little is known about how influenza vaccination impacts an individual's infectiousness, how vaccines wane over time, and the impact of repeated vaccination.

Protective effect of influenza vaccination on outcomes in geriatric stroke patients: A nationwide matched cohort study

BACKGROUND AND AIMS

The effects of influenza vaccination (IV) on stroke outcomes are unclear. The purpose of this study is to evaluate the outcomes after stroke in elderly individuals who have received an IV.

METHODS

We used Taiwan's National Health Insurance Research Database 2000-2009 claims data to conduct a nested stroke cohort study including 148,909 hospitalized stroke patients aged 66 years and older. Using a matching procedure by propensity score, we selected 25,248 stroke patients with IV and 25,248 stroke patients without IV for comparison. Logistic regression was used to calculate the odds ratios (ORs) and 95% CIs of post-stroke complications and in-hospital mortality associated with IV.

RESULTS

Stroke patients with IV had significantly lower risks of post-stroke pneumonia (OR = 0.79; 95% CI, 0.74-0.83), septicemia (OR = 0.78; 95% CI, 0.70-0.86), urinary tract infection (OR = 0.87; 95% CI, 0.83-0.92), and 30-day in-hospital mortality (OR = 0.60; 95% CI, 0.54-0.67) compared with non-IV stroke patients. Vaccinated stroke patients also had shorter hospital stays (p < 0.0001) and less medical expenditures (p < 0.0001) during stroke admission than the control group. Lower rates of post-stroke adverse events in patients with IV were noted in both sexes of all age groups with various types of stroke.

CONCLUSIONS

Stroke patients with IV showed fewer complications and lower mortality compared with non-IV patients. These findings suggest the urgent need to promote IV for this susceptible population of stroke patients.

Immunosenescence and Respiratory Infections Among Nursing Home Residents

Residents of nursing homes are at high risk of infectious complications due to respiratory infection. The nursing home setting places residents at high risk given the frequent contact among residents and by staff along with the possibility for continuous introduction of respiratory viruses from the community. Nursing home residents are among the most frail members of society. They have multiple comorbidities that can increase their risk of infection. Immunosenescence plays an important role in not only rendering these seniors susceptible in infection, particularly viral respiratory infection, but also interferes with protection. That is, the ability to mount a robust immune response to influenza and pneumococcal vaccine increase the risk. There have been a number of T cell deficits described in this population. CD4+ T cells, in particular T-regs and CMV-reactive CD4+ T cells, have been shown to be predictive of respiratory viral infection in this population. Although evidence exists that T cell subsets may correlate better with response to vaccine and protection, antibody responses to influenza vaccine remains an important correlate in this population. Large-scale epidemiologic studies are needed to establish better correlation between biomarkers for protection and respiratory and other pathogens that circulate in nursing homes.

The importance and implications of comparator selection in pharmacoepidemiologic research

PURPOSE OF REVIEW

Pharmacoepidemiologic studies employing large databases are critical to evaluating the effectiveness and safety of drug exposures in large and diverse populations. Because treatment is not randomized, researchers must select a relevant comparison group for the treatment of interest. The comparator group can consist of individuals initiating: (1) a similarly indicated treatment (active comparator), (2) a treatment used for a different indication (inactive comparator) or (3) no particular treatment (non-initiators). Herein we review recent literature and describe considerations and implications of comparator selection in pharmacoepidemiologic studies.

RECENT FINDINGS

Comparator selection depends on the scientific question and feasibility constraints. Because pharmacoepidemiologic studies rely on the choice to initiate or not initiate a specific treatment, rather than randomization, they are at-risk for confounding related to the comparator choice including: by indication, disease severity and frailty. We describe forms of confounding specific to pharmacoepidemiologic studies and discuss each comparator along with informative examples and a case study. We provide commentary on potential issues relevant to comparator selection in each study, highlighting the importance of understanding the population in whom the treatment is given and how patient characteristics are associated with the outcome.

SUMMARY

Advanced statistical techniques may be insufficient for reducing confounding in observational studies. Evaluating the extent to which comparator selection may mitigate or induce systematic bias is a critical component of pharmacoepidemiologic studies.

Controlling for Frailty in Pharmacoepidemiologic Studies of Older Adults: Validation of an Existing Medicare Claims-based Algorithm

BACKGROUND

Frailty is a geriatric syndrome characterized by weakness and weight loss and is associated with adverse health outcomes. It is often an unmeasured confounder in pharmacoepidemiologic and comparative effectiveness studies using administrative claims data.

METHODS

Among the Atherosclerosis Risk in Communities (ARIC) Study Visit 5 participants (2011-2013; n = 3,146), we conducted a validation study to compare a Medicare claims-based algorithm of dependency in activities of daily living (or dependency) developed as a proxy for frailty with a reference standard measure of phenotypic frailty. We applied the algorithm to the ARIC participants' claims data to generate a predicted probability of dependency. Using the claims-based algorithm, we estimated the C-statistic for predicting phenotypic frailty. We further categorized participants by their predicted probability of dependency (<5%, 5% to <20%, and ≥20%) and estimated associations with difficulties in physical abilities, falls, and mortality.

RESULTS

The claims-based algorithm showed good discrimination of phenotypic frailty (C-statistic = 0.71; 95% confidence interval [CI] = 0.67, 0.74). Participants classified with a high predicted probability of dependency (≥20%) had higher prevalence of falls and difficulty in physical ability, and a greater risk of 1-year all-cause mortality (hazard ratio = 5.7 [95% CI = 2.5, 13]) than participants classified with a low predicted probability (<5%). Sensitivity and specificity varied across predicted probability of dependency thresholds.

CONCLUSIONS

The Medicare claims-based algorithm showed good discrimination of phenotypic frailty and high predictive ability with adverse health outcomes. This algorithm can be used in future Medicare claims analyses to reduce confounding by frailty and improve study validity.

Observational studies and the difficult quest for causality: lessons from vaccine effectiveness and impact studies

Although randomized placebo-controlled trials (RCT) are critical to establish efficacy of vaccines at the time of licensure, important remaining questions about vaccine effectiveness (VE)-used here to include individual-level measures and population-wide impact of vaccine programmes-can only be answered once the vaccine is in use, from observational studies. However, such studies are inherently at risk for bias. Using a causal framework and illustrating with examples, we review newer approaches to detecting and avoiding confounding and selection bias in three major classes of observational study design: cohort, case-control and ecological studies. Studies of influenza VE, especially in seniors, are an excellent demonstration of the challenges of detecting and reducing such bias, and so we use influenza VE as a running example. We take a fresh look at the time-trend studies often dismissed as 'ecological'. Such designs are the only observational study design that can measure the overall effect of a vaccination programme [indirect (herd) as well as direct effects], and are in fact already an important part of the evidence base for several vaccines currently in use. Despite the great strides towards more robust observational study designs, challenges lie ahead for evaluating best practices for achieving robust unbiased results from observational studies. This is critical for evaluation of national and global vaccine programme effectiveness.

Excess mortality in Italy: Should we care about low influenza vaccine uptake?

AIMS

The aims of this study were to explore 2015 mortality data further and to assess excess deaths' determinants.

METHODS

We analysed data from a large metropolitan area in the north of Italy, the city of Bologna. We took advantage of a comprehensive local-level database and merged three different data sources to analitically explore reported 2014-2015 excess mortality and its determinants. Effect estimates were derived from multivariable Poisson regression analysis, according to vaccination status and frailty index.

RESULTS

We report 9.8% excess mortality in 2015 compared to 2014, with seasonal and age distribution patterns in line with national figures. All-cause mortality in the elderly population is 36% higher (risk ratio [RR]=1.36, 95% confidence interval [CI] 1.27-1.45) in subjects not vaccinated against seasonal flu compared to vaccinated subjects, with risk of death for influenza or pneumonia being 43% higher (RR=1.43, 95% CI 1.02-2.00) in unvaccinated subjects.

CONCLUSIONS

Reported excess mortality's determinants in Italy should be further explored. Elderly subjects not vaccinated against the flu appear to have increased risk of all-cause and cause-specific mortality compared to vaccinated subjects after accounting for possible confounders. Our findings raise awareness of the need to promote immunisation against the flu among elder populations and offer insights to plan and implement effective public-health interventions.

Controlling confounding by frailty when estimating influenza vaccine effectiveness using predictors of dependency in activities of daily living

PURPOSE

To improve control of confounding by frailty when estimating the effect of influenza vaccination on all-cause mortality by controlling for a published set of claims-based predictors of dependency in activities of daily living (ADL).

METHODS

Using Medicare claims data, a cohort of beneficiaries >65 years of age was followed from September 1, 2007, to April 12, 2008, with covariates assessed in the 6 months before follow-up. We estimated Cox proportional hazards models of all-cause mortality, with influenza vaccination as a time-varying exposure. We controlled for common demographics, comorbidities, and health care utilization variables and then added 20 ADL dependency predictors. To gauge residual confounding, we estimated pre-influenza season hazard ratios (HRs) between September 1, 2007 and January 5, 2008, which should be 1.0 in the absence of bias.

RESULTS

A cohort of 2 235 140 beneficiaries was created, with a median follow-up of 224 days. Overall, 52% were vaccinated and 4% died during follow-up. During the pre-influenza season period, controlling for demographics, comorbidities, and health care use resulted in a HR of 0.66 (0.64, 0.67). Adding the ADL dependency predictors moved the HR to 0.68 (0.67, 0.70). Controlling for demographics and ADL dependency predictors alone resulted in a HR of 0.68 (0.66, 0.70).

CONCLUSIONS

Results were consistent with those in the literature, with significant uncontrolled confounding after adjustment for demographics, comorbidities, and health care use. Adding ADL dependency predictors moved HRs slightly closer to the null. Of the comorbidities, health care use variables, and ADL dependency predictors, the last set reduced confounding most. However, substantial uncontrolled confounding remained.

Effect of Influenza Vaccination on Risk of Stroke: A Systematic Review and Meta-Analysis

Background: Despite the presence of a strong association between influenza infection and stroke, whether influenza vaccination reduces the risk of stroke is yet a matter of controversy. We conducted a meta-analysis to determine whether influenza vaccination protects against stroke. Methods: We searched PubMed, EMBASE, and the Cochrane Library from database inception date to November 18, 2016, without language restrictions, to identify studies investigating the effect of influenza vaccination on subsequent risk of stroke. We conducted a meta-analysis to quantify the risk of stroke in overall and subgroup analyses and calculated a pooled OR for developing stroke with a 95% CI. Publication bias was assessed by Begg's rank correlation test. Results: Eleven studies fulfilled our inclusion criteria. In a random-effects model, vaccinated individuals had a decreased risk of stroke compared with unvaccinated individuals (OR 0.82; 95% CI 0.75-0.91; p < 0.001). The relationship between influenza vaccination and stroke risk remained robust in subgroup analyses. The significant effect of influenza vaccination was associated with ascertainment of vaccination status and stage of prevention. Conclusion: Vaccination against influenza is associated with a lower risk of stroke. Well-designed prospective studies are needed to provide stronger evidence of the protective effect of influenza vaccination against stroke.

Lifestyle, socioeconomic characteristics, and medical history of elderly persons who receive seasonal influenza vaccination in a tax-supported healthcare system

BACKGROUND

Observational studies on effectiveness of influenza vaccination in the elderly are thought to be biased by healthier lifestyles and higher socioeconomic status among vaccinated vs. unvaccinated persons. We examined this hypothesis in a uniform tax-supported health care system with free-of-charge influenza vaccination to the elderly.

METHODS

We conducted a cross-sectional study among Danes aged 65-79years participating in a survey. We compared elderly persons with and without a recent (within six months) influenza vaccination in terms of (i) lifestyle and socioeconomic characteristics obtained from the survey and (ii) health factors including medical history provided by Danish registries. We compared the prevalence of study variables among vaccinated and unvaccinated persons using age- and sex-adjusted prevalence ratios (aPRs) with 95% confidence intervals (CIs).

RESULTS

Among the 4237 elderly persons completing the survey, 1718 (41%) had received an influenza vaccination. Vaccinated persons had more comorbidity than unvaccinated persons (aPR for high comorbidity level: 1.51 95% CI 1.24-1.84), were less likely to never have smoked (aPR: 0.88, 95% CI 0.80-0.97), and had a higher prevalence of physical inactivity (aPR: 1.08, 95% CI 1.03-1.13). Levels of education and income were similar in the two groups. Vaccinated persons had a higher prevalence of major physical limitations (aPR: 1.40, 95% CI 1.17-1.66) and need for assistance with activities of daily living (aPR: 1.29, 95% CI 1.13-1.47).

CONCLUSION

Elderly influenza vaccinated persons were not healthier in terms of lifestyle and burden of disease, did not have a higher socioeconomic status, and were more frail than unvaccinated persons.

Real-time real-world analysis of seasonal influenza vaccine effectiveness: method development and assessment of a population-based cohort in Stockholm County, Sweden, seasons 2011/12 to 2014/15

Real-world estimates of seasonal influenza vaccine effectiveness (VE) are important for early detection of vaccine failure. We developed a method for evaluating real-time in-season vaccine effectiveness (IVE) and overall seasonal VE. In a retrospective, register-based, cohort study including all two million individuals in Stockholm County, Sweden, during the influenza seasons from 2011/12 to 2014/15, vaccination status was obtained from Stockholm’s vaccine register. Main outcomes were hospitalisation or primary care visits for influenza (International Classification of Disease (ICD)-10 codes J09-J11). VE was assessed using Cox multivariate stratified and non-stratified analyses adjusting for age, sex, socioeconomic status, comorbidities and previous influenza vaccinations. Stratified analyses showed moderate VE in prevention of influenza hospitalisations among chronically ill adults ≥ 65 years in two of four seasons, and lower but still significant VE in one season; 53% (95% confidence interval (CI): 33–67) in 2012/13, 55% (95% CI: 25–73) in 2013/14 and 18% (95% CI: 3–31) in 2014/15. In conclusion, seasonal influenza vaccination was associated with substantial reductions in influenza-specific hospitalisation, particularly in adults ≥ 65 years with underlying chronic conditions. With the use of population-based patient register data on influenza-specific outcomes it will be possible to obtain real-time estimates of seasonal influenza VE.

Effectiveness of the influenza vaccine in preventing admission to hospital and death in people with type 2 diabetes

BACKGROUND

The health burden caused by seasonal influenza is substantial. We sought to examine the effectiveness of influenza vaccination against admission to hospital for acute cardiovascular and respiratory conditions and all-cause death in people with type 2 diabetes.

METHODS

We conducted a retrospective cohort study using primary and secondary care data from the Clinical Practice Research Datalink in England, over a 7-year period between 2003/04 and 2009/10. We enrolled 124 503 adults with type 2 diabetes. Outcome measures included admission to hospital for acute myocardial infarction (MI), stroke, heart failure or pneumonia/influenza, and death. We fitted Poisson regression models for influenza and off-season periods to estimate incidence rate ratios (IRR) for cohorts who had and had not received the vaccine. We used estimates for the summer, when influenza activity is low, to adjust for residual confounding.

RESULTS

Study participants contributed to 623 591 person-years of observation during the 7-year study period. Vaccine recipients were older and had more comorbid conditions compared with nonrecipients. After we adjusted for covariates and residual confounding, vaccination was associated with significantly lower admission rates for stroke (IRR 0.70, 95% confidence interval [CI] 0.53-0.91), heart failure (IRR 0.78, 95% CI 0.65-0.92) and pneumonia or influenza (IRR 0.85, 95% CI 0.74-0.99), as well as all-cause death (IRR 0.76, 95% CI 0.65-0.83), and a nonsignificant change for acute MI (IRR 0.81, 95% CI 0.62-1.04) during the influenza seasons.

INTERPRETATION

In this cohort of patients with type 2 diabetes, influenza vaccination was associated with reductions in rates of admission to hospital for specific cardiovascular events. Efforts should be focused on improvements in vaccine uptake in this important target group as part of comprehensive secondary prevention.

Frequency and impact of confounding by indication and healthy vaccinee bias in observational studies assessing influenza vaccine effectiveness: a systematic review

Background

Evidence on influenza vaccine effectiveness (VE) is commonly derived from observational studies. However, these studies are prone to confounding by indication and healthy vaccinee bias. We aimed to systematically investigate these two forms of confounding/bias.

Methods

Systematic review of observational studies reporting influenza VE and indicators for bias and confounding. We assessed risk of confounding by indication and healthy vaccinee bias for each study and calculated ratios of odds ratios (crude/adjusted) to quantify the effect of confounder adjustment. VE-estimates during and outside influenza seasons were compared to assess residual confounding by healthy vaccinee effects.

Results

We identified 23 studies reporting on 11 outcomes. Of these, 19 (83 %) showed high risk of bias: Fourteen due to confounding by indication, two for healthy vaccinee bias, and three studies showed both forms of confounding/bias. Adjustment for confounders increased VE on average by 12 % (95 % CI: 7–17 %; all-cause mortality), 9 % (95 % CI: 4–14 %; all-cause hospitalization) and 7 % (95 % CI: 4–10 %; influenza-like illness). Despite adjustment, nine studies showed residual confounding as indicated by significant off-season VE-estimates. These were observed for five outcomes, but more frequently for all-cause mortality as compared to other outcomes (p = 0.03) and in studies which indicated healthy vaccinee bias at baseline (p = 0.01).

Conclusions

Both confounding by indication and healthy vaccinee bias are likely to operate simultaneously in observational studies on influenza VE. Although adjustment can correct for confounding by indication to some extent, the resulting estimates are still prone to healthy vaccinee bias, at least as long as unspecific outcomes like all-cause mortality are used. Therefore, cohort studies using administrative data bases with unspecific outcomes should no longer be used to measure the effects of influenza vaccination.

Electronic supplementary material

The online version of this article (doi:10.1186/s12879-015-1154-y) contains supplementary material, which is available to authorized users.

Association Between Hospitalization With Community-Acquired Laboratory-Confirmed Influenza Pneumonia and Prior Receipt of Influenza Vaccination

IMPORTANCE

Few studies have evaluated the relationship between influenza vaccination and pneumonia, a serious complication of influenza infection.

OBJECTIVE

To assess the association between influenza vaccination status and hospitalization for community-acquired laboratory-confirmed influenza pneumonia.

DESIGN, SETTING, AND PARTICIPANTS

The Etiology of Pneumonia in the Community (EPIC) study was a prospective observational multicenter study of hospitalizations for community-acquired pneumonia conducted from January 2010 through June 2012 at 4 US sites. In this case-control study, we used EPIC data from patients 6 months or older with laboratory-confirmed influenza infection and verified vaccination status during the influenza seasons and excluded patients with recent hospitalization, from chronic care residential facilities, and with severe immunosuppression. Logistic regression was used to calculate odds ratios, comparing the odds of vaccination between influenza-positive (case) and influenza-negative (control) patients with pneumonia, controlling for demographics, comorbidities, season, study site, and timing of disease onset. Vaccine effectiveness was estimated as (1 - adjusted odds ratio) × 100%.

EXPOSURE

Influenza vaccination, verified through record review.

MAIN OUTCOMES AND MEASURES

Influenza pneumonia, confirmed by real-time reverse-transcription polymerase chain reaction performed on nasal/oropharyngeal swabs.

RESULTS

Overall, 2767 patients hospitalized for pneumonia were eligible for the study; 162 (5.9%) had laboratory-confirmed influenza. Twenty-eight of 162 cases (17%) with influenza-associated pneumonia and 766 of 2605 controls (29%) with influenza-negative pneumonia had been vaccinated. The adjusted odds ratio of prior influenza vaccination between cases and controls was 0.43 (95% CI, 0.28-0.68; estimated vaccine effectiveness, 56.7%; 95% CI, 31.9%-72.5%).

CONCLUSIONS AND RELEVANCE

Among children and adults hospitalized with community-acquired pneumonia, those with laboratory-confirmed influenza-associated pneumonia, compared with those with pneumonia not associated with influenza, had lower odds of having received influenza vaccination.

Controlling Time-Dependent Confounding by Health Status and Frailty: Restriction Versus Statistical Adjustment

Nonexperimental studies of preventive interventions are often biased because of the healthy-user effect and, in frail populations, because of confounding by functional status. Bias is evident when estimating influenza vaccine effectiveness, even after adjustment for claims-based indicators of illness. We explored bias reduction methods while estimating vaccine effectiveness in a cohort of adult hemodialysis patients. Using the United States Renal Data System and linked data from a commercial dialysis provider, we estimated vaccine effectiveness using a Cox proportional hazards marginal structural model of all-cause mortality before and during 3 influenza seasons in 2005/2006 through 2007/2008. To improve confounding control, we added frailty indicators to the model, measured time-varying confounders at different time intervals, and restricted the sample in multiple ways. Crude and baseline-adjusted marginal structural models remained strongly biased. Restricting to a healthier population removed some unmeasured confounding; however, this reduced the sample size, resulting in wide confidence intervals. We estimated an influenza vaccine effectiveness of 9% (hazard ratio = 0.91, 95% confidence interval: 0.72, 1.15) when bias was minimized through cohort restriction. In this study, the healthy-user bias could not be controlled through statistical adjustment; however, sample restriction reduced much of the bias.

Enhanced Estimates of the Influenza Vaccination Effect in Preventing Mortality: A Prospective Cohort Study

Mortality is a major end-point in the evaluation of influenza vaccine effectiveness. However, this effect is not well known, since most previous studies failed to show good control of biases. We aimed to estimate the effectiveness of influenza vaccination in preventing all-cause mortality in community-dwelling seniors.Since 2009, a population-based cohort study using healthcare databases has been conducted in Navarra, Spain. In 2 late influenza seasons, 2011/2012 and 2012/2013, all-cause mortality in the period January to May was compared between seniors (65 years or over) who received the trivalent influenza vaccine and those who were unvaccinated, adjusting for demographics, major chronic conditions, dependence, previous hospitalization, and pneumococcal vaccination.The cohort included 103,156 seniors in the 2011/2012 season and 105,140 in the 2012/2013 season (58% vaccinated). Seniors vaccinated in the previous season who discontinued vaccination (6% of the total) had excess mortality and were excluded to prevent frailty bias. The final analysis included 80,730 person-years and 2778 deaths. Vaccinated seniors had 16% less all-cause mortality than those unvaccinated (adjusted rate ratio [RR] = 0.84; 95% confidence interval 0.76-0.93). This association disappeared in the post-influenza period (adjusted RR = 0.96; 95% confidence interval 0.85-1.09). A similar comparison did not find an association in January to May of the 2009/2010 pandemic season (adjusted RR = 0.98; 95% confidence interval 0.84-1.14), when no effect of the seasonal vaccine was expected. On average, 1 death was prevented for every 328 seniors vaccinated: 1 for every 649 in the 65 to 74 year age group and 1 for every 251 among those aged 75 and over.These results suggest a moderate preventive effect and a high potential impact of the seasonal influenza vaccine against all-cause mortality. This reinforces the recommendation of annual influenza vaccination in seniors.

Vaccines for the prevention of seasonal influenza in patients with diabetes: systematic review and meta-analysis

BACKGROUND

Patients with diabetes are at increased risk of severe influenza disease; influenza vaccination for these patients is therefore recommended by the World Health Organization and several National Immunization Technical Advisory Groups. However, no systematic review has evaluated the effects of influenza vaccines for patients with diabetes.

METHODS

We conducted a systematic review and meta-analysis by searching Medline, Embase, Cochrane Central Register of Controlled Trials, and ClinicalTrials.gov from inception until November 2014. We included all types of studies reporting on the efficacy, effectiveness, and/or safety of influenza vaccination in patients with type 1 and type 2 diabetes of all ages. We used the Newcastle-Ottawa scale to assess risk of bias in observational studies. Residual confounding was addressed by comparing estimates of vaccine effectiveness (VE) during influenza seasons to those obtained during off-seasons. Quality of the evidence for each outcome was assessed using the GRADE methodology.

RESULTS

Following review of 1,444 articles, 11 observational studies with a total of 170,924 participants were included. In diabetic patients of working-age (18-64 years), influenza vaccination prevented all-cause hospitalization with a pooled VE of 58% (95% CI, 6-81%) and hospitalization due to influenza or pneumonia (VE 43%; 95% CI, 28-54%), whereas no effects on all-cause mortality and influenza-like illness (ILI) were observed. In the elderly (65+), influenza vaccination prevented all-cause mortality (VE 38%; 95% CI, 32-43%), all-cause hospitalization (VE 23%; 95% CI, 1-40%), hospitalization due to influenza or pneumonia (VE 45%; 95% CI, 34-53%), and ILI (VE 13%; 95% CI, 10-16%). However, significant off-season estimates for several outcomes indicated residual confounding, particularly in elderly patients. Quality of the evidence was low to very low for all outcomes. Laboratory-confirmed influenza infections were not reported.

CONCLUSIONS

Due to strong residual confounding in most of the identified studies, the available evidence is insufficient to determine the magnitude of benefit that diabetic people derive from seasonal influenza vaccination. Adequately powered randomized controlled trials or quasi-experimental studies using laboratory-confirmed influenza-specific outcomes are urgently needed.

Influenza vaccination in patients with end-stage renal disease: systematic review and assessment of quality of evidence related to vaccine efficacy, effectiveness, and safety

BACKGROUND

Vaccination against influenza is recommended in patients with end-stage renal disease (ESRD). However, so far, no systematic review has summarized the available evidence on the effectiveness and safety of influenza vaccination in this patient group.

METHODS

We conducted a systematic review and meta-analysis and assessed the quality of evidence using the GRADE methodology. We searched MEDLINE, EMBASE, Cochrane Library databases, ClinicalTrials.gov, and reference lists for studies on efficacy, effectiveness, and/or safety of seasonal influenza vaccination in patients with ESRD receiving dialysis. All reported clinical outcomes were considered, including all-cause mortality, cardiac death, infectious death, all-cause hospitalization, hospitalization due to influenza or pneumonia, hospitalization due to bacteremia, viremia, or septicemia, hospitalization due to respiratory infection, ICU admission, and influenza-like illness.

RESULTS

Five observational studies and no randomized-controlled trial were identified. In four studies, risk of bias was high regarding all reported outcomes. Strong residual confounding was likely to be present in one study reporting on three outcomes, as indicated by significant protective effects of vaccination outside influenza seasons. Therefore, the statistically significant protective effects on all-cause mortality (vaccine effectiveness (VE), 32%; 95% CI, 24-39%), cardiac death (VE, 16%; 95% CI, 1-29%), hospitalization due to influenza or pneumonia (VE, 14%; 95% CI, 7-20%), ICU admission (VE, 81%; 95% CI, 63-86%), and influenza-like illness (VE, 12%; 95% CI, 10-14%) have to be taken with caution. According to GRADE, the quality of the body of evidence was considered very low for all outcomes. No study reported on laboratory-confirmed influenza virus infections or on safety endpoints.

CONCLUSIONS

Evidence on the protective effects of influenza vaccination in patients with ESRD is limited and of very low quality. Since VE estimates in the available literature are prone to unmeasured confounding, studies using randomization or quasi-experimental designs are needed to determine the extent by which vaccination prevents influenza and related clinical outcomes in this at-risk population. However, given the high rates of health-endangering events in these patients, even a low VE can be considered as sufficient to recommend annual influenza vaccination.

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.

Using claims data to predict dependency in activities of daily living as a proxy for frailty

PURPOSE

Estimating drug effectiveness and safety among older adults in population-based studies using administrative health care claims can be hampered by unmeasured confounding as a result of frailty. A claims-based algorithm that identifies patients likely to be dependent, a proxy for frailty, may improve confounding control. Our objective was to develop an algorithm to predict dependency in activities of daily living (ADL) in a sample of Medicare beneficiaries.

METHODS

Community-dwelling respondents to the 2006 Medicare Current Beneficiary Survey, >65 years old, with Medicare Part A, B, home health, and hospice claims were included. ADL dependency was defined as needing help with bathing, eating, walking, dressing, toileting, or transferring. Potential predictors were demographics, International Classification of Diseases, Ninth Revision Clinical Modification diagnosis/procedure and durable medical equipment codes for frailty-associated conditions. Multivariable logistic regression was used to predict ADL dependency. Cox models estimated hazard ratios for death as a function of observed and predicted ADL dependency.

RESULTS

Of 6391 respondents, 57% were female, 88% white, and 38% were ≥80. The prevalence of ADL dependency was 9.5%. Strong predictors of ADL dependency were charges for a home hospital bed (OR = 5.44, 95%CI = 3.28-9.03) and wheelchair (OR = 3.91, 95%CI = 2.78-5.51). The c-statistic of the final model was 0.845. Model-predicted ADL dependency of 20% or greater was associated with a hazard ratio for death of 3.19 (95%CI: 2.78, 3.68).

CONCLUSIONS

An algorithm for predicting ADL dependency using health care claims was developed to measure some aspects of frailty. Accounting for variation in frailty among older adults could lead to more valid conclusions about treatment use, safety, and effectiveness.