Association of influenza vaccination and reduced risk of stroke hospitalization among the elderly: a population-based case-control study

Influenza vaccine effect on risk of stroke occurrence: a systematic review and meta-analysis

Background

Stroke is a significant global cause of mortality and long-term disability, potentially influenced by infections that heighten systemic inflammation and thrombotic events. The full impact of influenza vaccination on stroke remains uncertain. This systematic review and meta-analysis aimed to investigate the association between influenza immunization and stroke incidence.

Methods

We searched for randomized controlled trials (RCTs), case-control, and cohort studies published in PubMed/Medline, Cochrane-Central-Register-of-Controlled-Trials (CENTRAL), and Embase until 5 December 2022, and identified articles investigating the effect of influenza vaccine on stroke occurrence. All articles were screened by two independent reviewers. We performed a meta-analysis to investigate the risk of stroke occurrence in vaccinated vs. unvaccinated individuals. The random-effects model was used in all statistical analyses.

Results

Among the 26 articles meeting our criteria, 10 were retrospective cohort studies, 9 were case-control studies, 3 were prospective cohort studies, 3 were RCTs and 1 case-series. Overall, the studies showed a significant decrease in the risk of stroke incidence/hospitalization among vaccinated patients (OR = 0.81, 95% CI [0.77-0.86], p = 0.00001). Furthermore, studies showed flu vaccine decreases the occurrence of mortality among stroke patients (OR = 0.50, 95% CI [0.37-0.68], p = 0.00001). Sub-group analysis revealed significant protective effect for patients with specific comorbidities including atrial fibrillation (OR = 0.68, 95% CI [0.57-0.81], p = 0.0001), diabetes (OR = 0.76, 95% CI [0.66-0.87], p = 0.0001), Chronic obstructive pulmonary disease (OR = 0.70, 95% CI [0.61-0.81], p = 0.00001), and hypertension (OR = 0.76, 95% CI [0.70-83], p = 0.00001).

Conclusion

The current meta-analysis further supports prior findings that influenza vaccination reduces stroke risk, particularly in patients with comorbidities. Guidelines should promote vaccination for at-risk individuals.

Impact of influenza, herpes zoster, and pneumococcal vaccinations on the incidence of cardiovascular events in subjects aged over 65 years: a systematic review

This systematic review aims to summarize the impact of vaccination against influenza, shingles, and pneumococcus on the incidence on the risk of cardiovascular events in the elderly. This protocol was developed in accordance with PRISMA guidelines. We conducted a literature search and identified all relevant articles published regarding the matter up to September 2022. We retrieved 38 studies (influenza vaccine = 33, pneumococcal vaccine = 5, and zoster vaccine = 2). A total of 28 and 2 studies have shown that influenza and pneumococcal vaccines significantly lower the risk of cardiovascular disease in the elderly. Also, repeated influenza vaccination shows a consistent and dose-dependent protective effect against acute coronary syndromes and stroke. Moreover, dual influenza and pneumococcal vaccination was associated with lower risks of some cardiovascular events (stroke, congestive heart failure, ischemic heart disease, and myocardial infarction). However, the impact of PCV13 on cardiovascular events has not been studied, nor has the currently recommended vaccination schedule (PCV13 + PPV23). As for herpes zoster vaccination, only the protective effect against stroke has been studied with the live attenuated herpes zoster vaccine, but no studies have been conducted with the recombinant subunit herpes zoster vaccine. This review outlines the benefits of the vaccines mentioned above beyond their preventive action on infectious diseases. It is intended for health professionals who wish to inform and advise their elderly patients.

Pleiotropic Effects of Influenza Vaccination

Influenza vaccines are designed to mimic natural influenza virus exposure and stimulate a long-lasting immune response to future infections. The evolving nature of the influenza virus makes vaccination an important and efficacious strategy to reduce healthcare-related complications of influenza. Several lines of evidence indicate that influenza vaccination may induce nonspecific effects, also referred to as heterologous or pleiotropic effects, that go beyond protection against infection. Different explanations are proposed, including the upregulation and downregulation of cytokines and epigenetic reprogramming in monocytes and natural killer cells, imprinting an immunological memory in the innate immune system, a phenomenon termed "trained immunity". Also, cross-reactivity between related stimuli and bystander activation, which entails activation of B and T lymphocytes without specific recognition of antigens, may play a role. In this review, we will discuss the possible nonspecific effects of influenza vaccination in cardiovascular disease, type 1 diabetes, cancer, and Alzheimer's disease, future research questions, and potential implications. A discussion of the potential effects on infections by other pathogens is beyond the scope of this review.

A Systematic Review and Meta-Analysis of the Relationship between Receiving the Flu Vaccine with Acute Cerebrovascular Accident and Its Hospitalization in the Elderly

Background and Aims

In recent years, various studies have been conducted worldwide to investigate the relationship between receiving the flu vaccine with acute cerebrovascular accident or stroke and its hospitalization in the elderly; however, the results of these studies are contradictory. Therefore, this study was aimed at investigating the relationship between receiving the flu vaccine with stroke and its hospitalization in the elderly.

Methods

This study is a systematic review and meta-analysis of studies examining the relationship between receiving the flu vaccine with stroke and its hospitalization in the elderly during the years 1980 to 2021 which have been published in ISI Web of Science, Scopus PubMed, Cochrane, Science Direct, Google Scholar, and Embase. All analyses were performed by Stata 15, and the significance level in this study was considered <0.05.

Results

In the systematic search, 3088 articles were retrieved, considering the study criteria; finally, 14 studies were included in the meta-analysis. Based on the results of the meta-analysis, the odds ratio (OR) of occurrence and hospitalization of stroke compared to the nonvaccinated group in vaccine recipients is equal to 0.84 (95% confidence interval (CI): 0.78-0.90, P value ≤ 0.001). Publication bias was not observed in this study (P value = 0.101).

Conclusion

Getting the flu vaccine can reduce the risk of occurrence and hospitalization of stroke in the elderly by 16% (10%-22%). Therefore, receiving this vaccine as a preventive intervention for stroke in the elderly may be promising.

Influenza Vaccination and Risk of Ischemic Stroke: A Population-Based Case-Control Study

BACKGROUND AND OBJECTIVES

To assess the relationship between influenza vaccination in the general population and risk of a first ischemic stroke (IS) during pre-epidemic, epidemic, and postepidemic periods.

METHODS

A nested case-control study was conducted in a Spanish primary care database over 2001-2015. Individuals aged 40-99 years with at least 1 year registry and no history of stroke or cancer were selected to conform the source cohort, from which incident IS cases were identified and classified as cardioembolic or noncardioembolic. Five controls per case were randomly selected, individually matched with cases for exact age, sex, and date of stroke diagnosis (index date). A patient was considered vaccinated when he/she had a recorded influenza vaccination at least 14 days before the index date within the same season. Adjusted odds ratios (aORs) and their respective 95% CIs were computed through a conditional logistic regression. Pneumococcal vaccination was used as a negative control.

RESULTS

From a cohort of 3,757,621 patients, we selected 14,322 incident IS cases (9,542 noncardioembolic and 4,780 cardioembolic) and 71,610 matched controls. Of them, 41.4% and 40.5%, respectively, were vaccinated yielding a crude OR of 1.05 (95% CI 1.01-1.10). Vaccinated patients presented a higher prevalence of vascular risk factors, diseases, and comedication than those nonvaccinated, and after full adjustment, the association of influenza vaccination with IS yielded an aOR of 0.88 (95% CI 0.84-0.92), appearing early (aOR15-30 days 0.79; 95% CI 0.69-0.92) and slightly declining over time (aOR>150 days 0.92; 95% CI 0.87-0.98). A reduced risk of similar magnitude was observed with both types of IS, in the 3 epidemic periods, and in all subgroups analyzed (men, women, individuals younger and older than 65 years of age, and those with intermediate and high vascular risk). By contrast, pneumococcal vaccination was not associated with a reduced risk of IS (aOR 1.08; 95% CI 1.04-1.13).

DISCUSSION

Results are compatible with a moderate protective effect of influenza vaccine on IS appearing early after vaccination. The finding that a reduced risk was also observed in pre-epidemic periods suggests that either the "protection" is not totally linked to prevention of influenza infection or it may be partly explained by unmeasured confounding factors.

Association between influenza vaccination and risk of stroke in Alberta, Canada: a population-based study

BACKGROUND

Respiratory infection can be an immediate precursor to stroke and myocardial infarction. Influenza vaccination is associated with reduced risk of myocardial infarction and hospitalisation for cardiac disease, and influenza vaccination is strongly recommended for patients with heart disease. Evidence on whether the same protective association exists for stroke, and whether this potential effect is consistent across age and risk groups, is conflicting. We aimed to assess the risk of stroke after influenza vaccination in adults.

METHODS

We obtained administrative data from the Alberta Health Care Insurance Plan (which covers all residents of Alberta, Canada) beginning on Sept 30, 2009, or May 15 of the year in which residents were recorded as being 18 years of age. Individuals were censored at the earliest of three events: death, recorded outmigration, or Dec 31, 2018. The outcome of interest was any stroke event, comprising acute ischaemic stroke, intracerebral haemorrhage, subarachnoid haemorrhage, and transient ischaemic attack. We used Andersen-Gill Cox models to analyse the hazard of any stroke event for individuals with recent (&lt;182 days) influenza vaccination compared with those without recent influenza vaccination, with adjustment for age, sex, anticoagulant use, atrial fibrillation, chronic obstructive pulmonary disease, diabetes, hypertension, income quintile, and rural or urban home location. Two-way interaction terms between each individual covariate and vaccination status were used to assess for effect modification by risk factor. The association between vaccination and risk of each type of stroke was also modelled, adjusting for baseline covariates.

FINDINGS

The study sample consisted of 4 141 209 adults (29 687 899 person-years of observation time) registered under the provincial health-care system between Sept 30, 2009, and Dec 31, 2018. 1 769 565 (42·73%) individuals received at least one vaccination during the study period, and 38 126 stroke events were recorded. Adjusted for demographics and comorbidities, recent influenza vaccination significantly reduced the hazard of stroke (hazard ratio 0·775 [95% CI 0·757-0·793]). This association persisted across all stroke types. We found effect modification by each covariate examined except for home location; however, vaccination was associated with a reduced risk of stroke overall across all ages and risk profiles with the exception of individuals without hypertension.

INTERPRETATION

The risk of stroke is reduced among people who have recently been vaccinated against influenza compared with those who have not. This association extended to the entire adult population and was not limited to individuals with a baseline high risk of stroke. Further studies in a variety of settings are needed to evaluate whether influenza vaccination could be used as a public health strategy to prevent stroke.

FUNDING

None.

Individual and Joint Effects of Influenza-Like Illness and Vaccinations on Stroke in the Young: A Case-Control Study

BACKGROUND:

Influenza-like illness (ILI) is an acute trigger for stroke, although joint effects of vaccinations and ILI have not yet been explored.

METHODS:

Data for our case-control study was obtained from MarketScan Commercial Claims and Encounters between 2008 and 2014. Patients 18 to 65 years old who experienced a stroke were matched on age and admission date to a control, defined as patients with head trauma or ankle sprain at an inpatient or emergency department visit. Exposures were ILI in the prior 30 days, and any type of vaccination during the year prior. Our outcome was ischemic and intracerebral hemorrhagic strokes identified using International Classification of Diseases, Ninth Revision (ICD-9 ) codes. Logistic regression models estimated adjusted odds ratios (aORs) controlling for preventive care visits, diabetes, valvular heart disease, smoking, alcohol abuse, obesity, and hypertension.

RESULTS:

We identified and matched 24 103 cases 18 to 44 years old and 141 811 45 to 65 years old. Those aged 18 to 44 years had increased stroke risk 30 days after ILI (aOR, 1.68 [95% CI, 1.51–1.86]) and reduced risk with any vaccination in the year prior (aOR, 0.92 [95% CI, 0.87–0.99]). Joint effects indicate that ILI was associated with increased stroke risk among those with (aOR, 1.41 [95% CI, 1.08–1.85]) and without (aOR, 1.73 [95% CI, 1.55–1.94]) vaccinations in the prior year ( P interaction =0.16). Among those aged 45 to 65 years, adjusted analyses indicate increased stroke risk for those with ILI (aOR, 1.32 [95% CI, 1.26–1.38]), although there was no effect of vaccinations (aOR, 1.00 [95% CI, 0.97–1.02]). Joint effects indicate that ILI was not associated with stroke among those with any vaccination (aOR, 1.07 [95% CI, 0.96–1.18]) but was associated with increased risk among those without vaccinations ([aOR, 1.39 [95% CI, 1.32–1.47]; P interaction <0.001).

CONCLUSIONS:

ILI was associated with increased stroke risk in the young and middle-aged, while vaccinations of any type were associated with decreased risk among the young. Joint effects of ILI and vaccinations indicate vaccinations can reduce the effect of ILI on stroke.

The impact of influenza vaccination on cardiovascular disease

Influenza infection has been identified as a triggering or exacerbating factor for cardiovascular events. To analyse the effect of influenza vaccination on cardiovascular disease, a systematic search of studies published between 2009-2019 was conducted. All the studies that evaluated the effect of vaccination against influenza on cardiovascular events and their outcome were considered. Finally, 30 of the 1147 identified studies were included. These studies show a protective effect of the influenza vaccine on the development of cardiovascular events (myocardial infarction, cerebrovascular accidents, atrial fibrillation, and heart failure) and on the worsening of these conditions. Furthermore, the data showed that vaccinated patients have a lower risk of death from cardiovascular pathologies. Influenza vaccination is therefore an effective measure in the prevention of cardiovascular diseases both in patients with established cardiovascular disease and in the population without previous coronary pathology.

Knowledge, Attitudes and Practices of Flu Vaccination in Hemodialysis Patients

BACKGROUND

Hemodialysis (HD) patients have an increased risk of morbidity and mortality due to infections. Despite the positive effect of vaccinations, the implementation of this method of prophylaxis is low.

OBJECTIVES

This study aimed to explore the knowledge, attitudes and practices of flu vaccination among HD patients of two different dialysis centers.

METHODS

A total of 193 patients (mean age 63.6 years), who voluntarily agreed to participate in an anonymous survey related to influenza vaccination, were enrolled in this cross-sectional study.

RESULTS

A total of 45% of patients declared that they took regular, annual flu vaccination. In this group, 87.4% believed that vaccinations were effective. This opinion strongly correlated with the frequency of regular vaccinations (r = 0.56, p < 0.01). Multivariate logistic regression revealed that this opinion is an independent predictor of regular vaccinations with adjusted OR 9.86 (95% CI 4.36, 22.33). Groups of patients who had been irregularly or never vaccinated reject vaccinations for the following reasons: fear of adverse events-29.2%, conviction that vaccination was ineffective-26.4%, and lack of information about vaccination-22.6%.

CONCLUSION

Knowledge among HD patients about the benefits of vaccinations is poor. Therefore, educational activities are required. Active vaccination promotion and education of patients rejecting this method of prevention play a key role in improving standards of care for HD patients.

Influenza-associated cardiovascular mortality in older adults in Beijing, China: a population-based time-series study

OBJECTIVE

This study comprehensively estimated the excess cardiovascular disease (CVD) mortality attributable to influenza in an older (age ≥65 years) population.

DESIGN

Ecological study.

SETTING

Aggregated data from administrative systems on CVD mortality, influenza surveillance and meteorological data in Beijing, China.

MAIN OUTCOME MEASURE

Excess overall CVD, and separately for ischaemic heart disease (IHD), ischaemic stroke, haemorrhagic stroke mortality attributable to influenza, adjusting for influenza activity, time trend, seasonality and ambient temperature.

RESULTS

CVD (risk ratio (RR) 1.02, 95% CI 1.01, 1.02), IHD (RR 1.01, 95% CI 1.01, 1.02), ischaemic stroke (RR=1.03, 95% CI 1.02, 1.04), but not haemorrhagic stroke (RR=1.00, 95% CI 0.99, 1.01) mortality, were significantly associated with every 10% increase in influenza activity. An increase in circulating A(H1N1)09pdm, A(H3N2) and B type virus were all significantly associated with CVD and ischaemic stroke mortality, but only A(H3N2) and B type virus with IHD mortality. The strongest increase in disease mortality was in the same week as the increase in influenza activity. Annual excess CVD mortality rate attributable to influenza ranged from 54 to 96 per 100 000 population. The 3%-6% CVD mortality attributable to influenza activity was related to an annual excess of 916-1640 CVD deaths in Beijing, China.

CONCLUSIONS

Influenza activity has moderate to strong associations with CVD, IHD and ischaemic stroke mortality in older adults in China. Promoting influenza vaccination could have major health benefit in this population.

BACKGROUND

Influenza may trigger serious CVD events. An estimation of excess CVD mortality attributable to influenza has particular relevance in China where vaccination is low and CVD burden is high.

METHODS

This study analysed data at the population level (age ≥65 years) using linked aggregated data from administrative systems on CVD mortality, influenza surveillance and meteorological data during 2011 to 2018. Quasi-Poisson regression models were used to estimate the excess overall CVD, and separately for IHD, ischaemic stroke, haemorrhagic stroke mortality attributable to influenza, adjusting for influenza activity, time trend, seasonality and ambient temperature. Analyses were also undertaken for influenza subtypes (A(H1N1)09pdm, A(H3N2) and B viruses), and mortality risk with time lags of 1-5 weeks following influenza activity in the current week.

Infection as a Stroke Risk Factor and Determinant of Outcome After Stroke

Understanding the relationship between infection and stroke has taken on new urgency in the era of the coronavirus disease 2019 (COVID-19) pandemic. This association is not a new concept, as several infections have long been recognized to contribute to stroke risk. The association of infection and stroke is also bidirectional. Although infection can lead to stroke, stroke also induces immune suppression which increases risk of infection. Apart from their short-term effects, emerging evidence suggests that poststroke immune changes may also adversely affect long-term cognitive outcomes in patients with stroke, increasing the risk of poststroke neurodegeneration and dementia. Infections at the time of stroke may also increase immune dysregulation after the stroke, further exacerbating the risk of cognitive decline. This review will cover the role of acute infections, including respiratory infections such as COVID-19, as a trigger for stroke; the role of infectious burden, or the cumulative number of infections throughout life, as a contributor to long-term risk of atherosclerotic disease and stroke; immune dysregulation after stroke and its effect on the risk of stroke-associated infection; and the impact of infection at the time of a stroke on the immune reaction to brain injury and subsequent long-term cognitive and functional outcomes. Finally, we will present a model to conceptualize the many relationships among chronic and acute infections and their short- and long-term neurological consequences. This model will suggest several directions for future research.

Effects of influenza vaccination on the risk of cardiovascular and respiratory diseases and all-cause mortality

BACKGROUND

Influenza vaccination is a simple strategy recommended for the prevention of influenza infection and its complications. This meta-analysis aimed to provide current supportive evidence for the breadth and validity of the observed protective effects of influenza vaccination on cardiovascular and respiratory adverse outcomes and all-cause mortality in older adults and in general adult population.

METHODS

We searched PubMed, Embase, Web of Science, and the Cochrane Library to identify all published studies comparing influenza vaccination with placebo from the database inception to November 11, 2018. These included studies reporting the associations of influenza vaccination with the risk of aforementioned adverse outcomes.

RESULTS

The pooled adjusted relative risks among influenza-vaccinated people relative to unvaccinated people for the outcomes of interest were 0.74 (95 % confidence interval [CI] = 0.70-0.78) for cardiovascular diseases (63 studies), 0.82 (95 % CI = 0.75-0.91) for respiratory diseases (29 studies), and 0.57 (95 % CI = 0.51-0.63) for all-cause mortality (43 studies). We performed subgroup analysis of age, sex, and region/country and found that these protective effects were evident in the general adult population and particularly robust in older adults and in those with pre-existing specific diseases.

CONCLUSION

Influenza vaccine is associated with a significant risk reduction of cardiovascular and respiratory adverse outcomes as well as all-cause mortality. Such a preventative measure can benefit the general population as well as those in old age and with pre-existing specific diseases.

Influenza vaccination as a novel means of preventing coronary heart disease: Effectiveness in older adults

Atherosclerosis can have various etiologies, including several newly recognized immunoinflammatory mechanisms. A growing body of evidence suggests that influenza infection is chronologically linked to acute myocardial infarction (AMI), and thus that the virus is a novel cardiovascular disease (CVD) risk factor. Morbidity and mortality rates for both influenza infection and AMI rise markedly with age. Epidemiological studies have demonstrated that influenza vaccination (IV) has a cardioprotective effect, especially in people aged 65 and over; hence, IV may be of value in the management of CVD. These observations justify efforts to better understand the underlying mechanisms and to identify therapeutic targets in older adults. In view of the above, the objective of the present study was to review the literature data on the cellular mechanisms that link IV to the prevention of atherosclerotic complications. Given the greater burden of CVD in older subjects, we also questioned the impact of aging on this association. The most widely recognized benefit of IV is the prevention of influenza infection and the latter's cardiovascular complications. In a new hypothesis, however, an influenza-independent effect is driven by vaccine immunity and modulation of the ongoing immunoinflammatory response in individuals with CVD. Although influenza infection and IV both induce a proinflammatory response, they have opposite effects on the progression of atherosclerosis - suggesting a hormetic phenomenon. Aging is characterized by chronic inflammation (sometimes referred to as "inflammaging") that progresses insidiously during the course of aging-related diseases, including CVD. It remains to be determined whether vaccination has an effect on aging-related diseases other than CVD. Although the studies of this topic had various limitations, the results highlight the potential benefits of vaccination in protecting the health of older adults, and should drive research on the molecular immunology of the response to IV and its correlation with atheroprotective processes.

Infection During Delivery Hospitalization and Risk of Readmission for Postpartum Stroke

Background and Purpose- Most cases of pregnancy-related ischemic stroke (IS) and hemorrhagic stroke (HS) occur postpartum. Infections have been identified as a trigger for strokes in young people and have been associated with strokes during delivery hospitalizations, but a temporal relationship has been difficult to establish. We hypothesized that infections diagnosed during a delivery admission would be associated with an increased risk of readmission for postpartum stroke. Methods- We conducted a retrospective cohort study using the Healthcare Cost and Utilization Project's National Readmissions Database from 2010 to 2014. Using weighted survey design Poisson regression analysis, we calculated adjusted risk ratios (aRR) and 95% CI for the association between infection during delivery admission and 30-day postpartum readmission for IS or HS. Results- Out of 17.2 million delivery admissions during the study period, 2128 were readmitted within 30 days for a stroke of any type. There were 1189 HS (intracerebral hemorrhage or subarachnoid hemorrhage) and 720 IS, and the remainder unspecified pregnancy-related stroke. Adjusting for age and comorbidities, women with delivery infections were at higher risk of readmission for postpartum stroke of any type (aRR, 1.19; 95% CI, 1.01-1.41). Women with infections had higher risk of readmission for postpartum IS (aRR, 1.75; 95% CI, 1.37-2.22), but not for postpartum HS (aRR, 0.96; 95% CI, 0.75-1.23). The effect of infection on 30-day IS readmission was larger in women without hypertensive disorders of pregnancy (aRR, 2.0; 95% CI, 1.55-2.69 in women without hypertensive disorders of pregnancy versus aRR, 1.47; 95% CI, 0.9-2.38 in women with hypertensive disorders of pregnancy, P value for interaction=0.09). Conclusions- Infection during delivery hospitalization was associated with increased risk of readmission for IS, but not HS, within 30 days postpartum, particularly in women without hypertensive disorders of pregnancy. Infection may play a role in triggering postpartum IS even in the absence of other risk factors.

Impact of influenza vaccination on healthcare utilization - A systematic review

INTRODUCTION

Although a vaccine-preventable disease, influenza causes approximately 3-5 million cases of severe illness and about 290,000-650,000 deaths worldwide, which occur primarily among people 65 years and older. Nonetheless, prevention of influenza and its complications rely mainly on vaccination. We aimed to systematically evaluate influenza vaccine effectiveness at reducing healthcare utilization in older adults, defined as the reduction of outpatient visits, ILI and influenza hospitalizations, utilization of antibiotics and cardiovascular events by vaccination status during the influenza season.

METHODS

We searched MEDLINE, EMBASE, CINAHL, Cochrane Library and considered any seasonal influenza vaccine, excluding the pandemic (2009-10 season) vaccine. Reviewers independently assessed data extraction and quality assessment.

RESULTS

Of the 8308 citations retrieved, 22 studies were included in the systematic review. Overall, two studies (9%) were deemed at moderate risk of bias, thirteen (59%) at serious risk of bias and seven (32%) at critical risk of bias. For outpatient visits, we found modest evidence of protection by the influenza vaccine. For all-cause hospitalization outcomes, we found a wide range of results, mostly deemed at serious risk of bias. The included studies suggested that the vaccine may protect older adults against influenza hospitalizations and cardiovascular events. No article meeting our inclusion criteria explored the use of antibiotics and ILI hospitalizations. The high heterogeneity between studies hindered the aggregation of data into a meta-analysis.

CONCLUSION

The variability between studies prevented us from drawing a clear conclusion on the effectiveness of the influenza vaccine on healthcare utilization in older adults. Overall, the data suggests that the vaccine may result in a reduction of healthcare utilization in the older population. Further studies of higher quality are necessary.

[Mortality due to cerebrovascular disease among the elderly and vaccination against influenza: São Paulo State, Brazil, 1980-2012]

This study describes the trend of the coefficients of mortality due to cerebrovascular diseases (CbVD) among the elderly in São Paulo State, Brazil, from 1980 to 2012, before and after influenza vaccination campaigns, and identifies change points. It is an ecological, time-series study carried out with death data from the Health Ministry's Mortality Information System and population data from the Brazilian Institute of Geography and Statistics. We used linear, polynomial and joinpoint regression models in the data analysis. Between 1980 and 2012, there were 480,955 deaths due to CbVD. The mean mortality coefficients decreased for both sexes in all age groups we analyzed, with the greatest reduction in the older ages and male sex. We observed a significant reduction in the mortality trend in 1998 for male sex in the age group 60-69 years (annual percent change - APC = -3%, 95%CI: -4.3; -1.6) and for all elderly (APC = -3.8%, 95%CI: -4.4; -3.1). Considering the period as a whole, we did not observe change points for the age group 70-79 (average annual percent change - AAPC = -3.3%, 95%CI: -3.5; -3.1) and, for male sex, for the group ≥ 80 years (AAPC = -2.9%, 95%CI: -3.1; -2.6). For all elderly, the mean percentage reduction was of 3.1% per year (AAPC = -3.1%, 95%CI: -3.5; -2.7). Results show a reduction in the mortality due to CbVD in the period, with different percentage variations in coefficient reduction. The study's findings add information to the debate regarding possible effects of vaccination campaigns in reducing mortality due to CbVD among the elderly.

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.

Aberrant coagulation causes a hyper-inflammatory response in severe influenza pneumonia

Influenza A virus (IAV) infects the respiratory tract in humans and causes significant morbidity and mortality worldwide each year. Aggressive inflammation, known as a cytokine storm, is thought to cause most of the damage in the lungs during IAV infection. Dysfunctional coagulation is a common complication in pathogenic influenza, manifested by lung endothelial activation, vascular leak, disseminated intravascular coagulation and pulmonary microembolism. Importantly, emerging evidence shows that an uncontrolled coagulation system, including both the cellular (endothelial cells and platelets) and protein (coagulation factors, anticoagulants and fibrinolysis proteases) components, contributes to the pathogenesis of influenza by augmenting viral replication and immune pathogenesis. In this review, we focus on the underlying mechanisms of the dysfunctional coagulatory response in the pathogenesis of IAV.

Infection and Stroke: an Update on Recent Progress

The role of infection in cerebrovascular disease is complex and remains incompletely understood. Over the last 5 years, investigators have made notable inroads in untangling this thorny topic. In this review, we examine these recent developments, concentrating on four aspects of the relationship between infection and stroke. We first discuss specific infectious agents as direct causes of stroke, focusing on recent work implicating herpesviruses and HIV in cerebral vasculopathy. We then discuss systemic infection of any type as a stroke trigger, focusing on the relationship of infection to timing of acute stroke, both in children and adults, as well as the role of vaccination in stroke prevention. We examine the evidence for chronic infection or "infectious burden" as a stroke risk factor. Finally, we discuss recent work on infection as a risk factor for increased morbidity after stroke, possible mechanisms mediating this effect, and the evidence for prophylactic antibiotics.

Influenza vaccination coverage among adults in Korea: 2008-2009 to 2011-2012 seasons

The aim of this study was to examine seasonal and pandemic influenza vaccination coverage in adults from the 2008-2009 season to the 2011-2012 season, including pandemic and post-pandemic seasons in Korea. We collected data of self-reported vaccine use from the Korean Community Health Survey. We also collected information on socioeconomic status and health behaviors in subpopulations. We tested for linear trends among the data to investigate vaccine coverage before and after the pandemic; and multiple logistic regression analyses were performed to identify predictors of obtaining the influenza vaccination. The results revealed a steady increase in vaccination coverage in every subgroup during four consecutive seasons. The highest rate of vaccine coverage (43.6%) occurred two years after the pandemic. Factors associated with vaccine receipt were: older age; lower education level; lower income; and health behaviors such as regular walking and receiving a health check-up. Smoking and drinking alcohol were inversely associated with vaccination. Having a chronic health condition was also a strong predictor of vaccine receipt. Though vaccination coverage rates were high in high-risk groups; disparities in coverage rates were substantial; particularly in young adults. Interventions are needed to minimize the coverage gaps among subgroups and to improve overall vaccination rates.