Challenges in evaluating influenza vaccine effectiveness and the mortality benefits controversy

COVID-19 Vaccine Uptake and Effectiveness by Time since Vaccination in the Western Cape Province, South Africa: An Observational Cohort Study during 2020-2022

There are few data on the real-world effectiveness of COVID-19 vaccines and boosting in Africa, which experienced widespread SARS-CoV-2 infection before vaccine availability. We assessed the association between vaccination and severe COVID-19 in the Western Cape, South Africa, in an observational cohort study of >2 million adults during 2020-2022. We described SARS-CoV-2 testing, COVID-19 outcomes, and vaccine uptake over time. We used multivariable cox models to estimate the association of BNT162b2 and Ad26.COV2.S vaccination with COVID-19-related hospitalization and death, adjusting for demographic characteristics, underlying health conditions, socioeconomic status proxies, and healthcare utilization. We found that by the end of 2022, 41% of surviving adults had completed vaccination and 8% had received a booster dose. Recent vaccination was associated with notable reductions in severe COVID-19 during periods dominated by Delta, and Omicron BA.1/2 and BA.4/5 (sub)lineages. During the latest Omicron BA.4/5 wave, within 3 months of vaccination or boosting, BNT162b2 and Ad26.COV2.S were each 84% effective against death (95% CIs: 57-94 and 49-95, respectively). However, distinct reductions of effectiveness occurred at longer times post completing or boosting vaccination. Results highlight the importance of continued emphasis on COVID-19 vaccination and boosting for those at high risk of severe COVID-19, even in settings with widespread infection-induced immunity.

COVID-19 vaccine uptake and effectiveness by time since vaccination in the Western Cape province, South Africa: An observational cohort study during 2020-2022

Background

There are few data on the real-world effectiveness of COVID-19 vaccines and boosting in Africa, which experienced high levels of SARS-CoV-2 infection in a mostly vaccine-naïve population, and has limited vaccine coverage and competing health service priorities. We assessed the association between vaccination and severe COVID-19 in the Western Cape, South Africa.

Methods

We performed an observational cohort study of >2 million adults during 2020-2022. We described SARS-CoV-2 testing, COVID-19 outcomes, and vaccine uptake over time. We used multivariable cox models to estimate the association of BNT162b2 and Ad26.COV2.S vaccination with COVID-19-related hospitalisation and death, adjusting for demographic characteristics, underlying health conditions, socioeconomic status proxies and healthcare utilisation.

Results

By end 2022, only 41% of surviving adults had completed vaccination and 8% a booster dose, despite several waves of severe COVID-19. Recent vaccination was associated with notable reductions in severe COVID-19 during distinct analysis periods dominated by Delta, Omicron BA.1/2 and BA.4/5 (sub)lineages: within 6 months of completing vaccination or boosting, vaccine effectiveness was 46-92% for death (range across periods), 45-92% for admission with severe disease or death, and 25-90% for any admission or death. During the Omicron BA.4/5 wave, within 3 months of vaccination or boosting, BNT162b2 and Ad26.COV2.S were each 84% effective against death (95% CIs: 57-94 and 49-95, respectively). However, there were distinct reductions of VE at larger times post completing or boosting vaccination.

Conclusions

Continued emphasis on regular COVID-19 vaccination including boosting is important for those at high risk of severe COVID-19 even in settings with widespread infection-induced immunity.

Roles for Pathogen Interference in Influenza Vaccination, with Implications to Vaccine Effectiveness (VE) and Attribution of Influenza Deaths

Pathogen interference is the ability of one pathogen to alter the course and clinical outcomes of infection by another. With up to 3000 species of human pathogens the potential combinations are vast. These combinations operate within further immune complexity induced by infection with multiple persistent pathogens, and by the role which the human microbiome plays in maintaining health, immune function, and resistance to infection. All the above are further complicated by malnutrition in children and the elderly. Influenza vaccination offers a measure of protection for elderly individuals subsequently infected with influenza. However, all vaccines induce both specific and non-specific effects. The specific effects involve stimulation of humoral and cellular immunity, while the nonspecific effects are far more nuanced including changes in gene expression patterns and production of small RNAs which contribute to pathogen interference. Little is known about the outcomes of vaccinated elderly not subsequently infected with influenza but infected with multiple other non-influenza winter pathogens. In this review we propose that in certain years the specific antigen mix in the seasonal influenza vaccine inadvertently increases the risk of infection from other non-influenza pathogens. The possibility that vaccination could upset the pathogen balance, and that the timing of vaccination relative to the pathogen balance was critical to success, was proposed in 2010 but was seemingly ignored. Persons vaccinated early in the winter are more likely to experience higher pathogen interference. Implications to the estimation of vaccine effectiveness and influenza deaths are discussed.

Targeting Inflammation and Immunosenescence to Improve Vaccine Responses in the Elderly

One of the most appreciated consequences of immunosenescence is an impaired response to vaccines with advanced age. While most studies report impaired antibody responses in older adults as a correlate of vaccine efficacy, it is now widely appreciated that this may fail to identify important changes occurring in the immune system with age that may affect vaccine efficacy. The impact of immunosenescence on vaccination goes beyond the defects on antibody responses as T cell-mediated responses are reshaped during aging and certainly affect vaccination. Likewise, age-related changes in the innate immune system may have important consequences on antigen presentation and priming of adaptive immune responses. Importantly, a low-level chronic inflammatory status known as inflammaging has been shown to inhibit immune responses to vaccination and pharmacological strategies aiming at blocking baseline inflammation can be potentially used to boost vaccine responses. Yet current strategies aiming at improving immunogenicity in the elderly have mainly focused on the use of adjuvants to promote local inflammation. More research is needed to understand the role of inflammation in vaccine responses and to reconcile these seemingly paradoxical observations. Alternative approaches to improve vaccine responses in the elderly include the use of higher vaccine doses or alternative routes of vaccination showing only limited benefits. This review will explore novel targets and potential new strategies for enhancing vaccine responses in older adults, including the use of anti-inflammatory drugs and immunomodulators.

Effect of Influenza Vaccination on Mortality and Risk of Hospitalization in Elderly Individuals with and without Disabilities: A Nationwide, Population-Based Cohort Study

Purpose: The effects of influenza vaccines are unclear for elderly individuals with disabilities. We use a population-based cohort study to estimate the effects of influenza vaccines in elderly individuals with and without disabilities. Methods: Data were taken from the National Health Insurance Research Database and Disabled Population Profile of Taiwan. A total of 2,741,403 adults aged 65 or older were identified and 394,490 were people with a disability. These two groups were further divided into those who had or had not received an influenza vaccine. Generalized estimating equations (GEE) were used to compare the relative risks (RRs) of death and hospitalization across the four groups. Results: 30.78% elderly individuals without a disability and 34.59% elderly individuals with a disability had vaccinated for influenza. Compared to the unvaccinated elderly without a disability, the vaccinated elderly without a disability had significantly lower risks in all-cause mortality (RR = 0.64) and hospitalization for any of the influenza-related diseases (RR = 0.91). Both the unvaccinated and vaccinated elderly with a disability had significantly higher risks in all-cause mortality (RR = 1.81 and 1.18, respectively) and hospitalization for any of the influenza-related diseases (RR = 1.73 and 1.59, respectively). Conclusions: The elderly with a disability had higher risks in mortality and hospitalization than those without a disability; however, receiving influenza vaccinations could still generate more protection to the disabled elderly.

Influenza Vaccine Effectiveness Against Influenza-Related Mortality in Australian Hospitalized Patients: A Propensity Score Analysis

Background

Data on influenza vaccine effectiveness (IVE) against mortality are limited, with no Australian data to guide vaccine uptake. We aimed to assess IVE against influenza-related mortality in Australian hospitalized patients, assess residual confounding in the association between influenza vaccination and mortality, and assess whether influenza vaccination reduces the severity of influenza illness.

Methods

Data were collected between 2010 and 2017 from a national Australian hospital-based sentinel surveillance system using a case-control design. Adults and children admitted to the 17 study hospitals with acute respiratory symptoms were tested for influenza using nucleic acid testing; all eligible test-positive cases, and a subset of test-negative controls, were included. Propensity score analysis and multivariable logistic regression were used to determine the adjusted odds ratio (aOR) of vaccination, with IVE = 1 – aOR × 100%. Residual confounding was assessed by examining mortality in controls.

Results

Over 8 seasons, 14038 patients were admitted with laboratory-confirmed influenza. The primary analysis included 9298 cases and 6451 controls, with 194 cases and 136 controls dying during hospitalization. Vaccination was associated with a 31% (95% confidence interval [CI], 3%–51%; P = .033) reduction in influenza-related mortality, with similar estimates in the National Immunisation Program target group. Residual confounding was identified in patients ≥65 years old (aOR, 1.92 [95% CI, 1.06–3.46]; P = .031). There was no evidence that vaccination reduced the severity of influenza illness (aOR, 1.07 [95% CI, .76–1.50]; P = .713).

Conclusions

Influenza vaccination is associated with a moderate reduction in influenza-related mortality. This finding reinforces the utility of the Australian vaccination program in protecting those most at risk of influenza-related deaths.

Influenza vaccination effectiveness for people aged under 65 years in Japan, 2013/2014 season: application of a doubly robust method to a large-scale, real-world dataset

BACKGROUND

Influenza vaccination is recognized as a primary public health intervention which prevents the illness of patients and relieves the societal burdens of influenza for medical community as well as the economy. To date, no effectiveness study of influenza vaccination has been conducted including a large population with a wide age span, in Japan. Here, we evaluated the clinical effectiveness of influenza vaccination in a large Japanese population.

METHODS

We conducted a cohort study using a large-scale claims database for employee health care insurance plans. Vaccination status was identified using plan records for influenza vaccination subsidies. We excluded people aged 65 years or more because of the unavailability of vaccination records. Effectiveness of vaccination in preventing influenza and its complication was evaluated with doubly robust methods using inversed probability treatment weighting to adjust health conscious behaviours and other confounders.

RESULTS

During the 2013/2014 influenza season, 369,425 subjects with age range from 1 to 64 years were eligible. Vaccination rate was 39.5% and an estimated odds ratio (OR) for influenza onset was 0.775 after doubly robust adjustment. Age-stratified ORs were significantly reduced in all age groups; lowest in subjects aged 1 to 4 years (0.600) and highest in those aged 13 to 19 (0.938). ORs for all the influenza complication outcomes were also statistically significant (0.403-0.709).

CONCLUSIONS

We confirmed the clinical effectiveness of influenza vaccination in people aged 1 to 64 years. Influenza vaccination significantly prevented influenza onset and was more effective in reducing secondary risks of influenza complications.

Interventions to Increase the Rate of Influenza and Pneumococcal Vaccination in Patients with Chronic Obstructive Pulmonary Disease: A Scoping Review

Background and Objective: Current evidence suggests that patients with chronic obstructive pulmonary disease (COPD) should receive influenza and pneumococcal vaccinations. Despite international guidelines recommending vaccination in patients with COPD, many patients remain unvaccinated. Reasons for vaccine non-acceptance are multifaceted and are likely to be influenced by multiple psychosocial factors and pre-existing health beliefs. The aim of this review was to identify interventions which have been shown to effectively increase vaccination rates in patients with COPD. Materials and Methods: A structured search of PubMed returned 491 titles. Following title and abstract screening, seven full-text articles reporting on 6 unique interventional studies were extracted for narrative synthesis. A variety of interventions were investigated which, for the purposes of this review, were grouped into patient-focussed, clinician-focussed and mixed interventions. Results: Three papers reported findings from clinical trials (2 unique studies) and 4 papers reported findings from before-after studies. Two studies were conducted in the primary care setting, the remaining studies were conducted in secondary and tertiary care. Most studies reported both influenza and pneumococcal vaccination rates. These studies suggest that multimodal interventions, which target multiple aspects of evidence-based care and use both patient-focussed and clinician-focussed techniques, may have the greatest impact on vaccination rates in patients with COPD. Conclusions: Further, adequately powered, high quality studies are needed. It is crucial for individual institutions to monitor their own vaccination rates to determine if there is scope for performance improvement.

Estimating influenza vaccine effectiveness: Evolution of methods to better understand effects of confounding in older adults

Older adults are at high risk for serious complications of influenza illness and loss of vaccine-mediated protection. It is increasingly recognized that in addition to age, multiple chronic conditions and associated frailty contribute to the decline in vaccine effectiveness in this population. However, observational studies have been fraught with issues of confounding related to the degree of frailty and functional decline, measures of which are not included in standard administrative health care databases that are used to calculate vaccine effectiveness. This issue has led to the identification of confounding by indication or from "healthy vaccinee" bias, which respectively lead to underestimates or overestimates of influenza vaccine effectiveness. In addition, the sensitivity and specificity of the criteria used to define influenza-like illness declines with increasing age due to atypical presentations of illness and the inability to distinguish between influenza and other respiratory viruses. The test-negative case:control design has emerged as a method to estimate influenza vaccine effectiveness by comparing vaccination rates in those with laboratory-confirmed influenza to those with other acute viral respiratory illnesses. This review provides a perspective on how test-negative case:control study designs and new insights into mechanisms of protection have considerably strengthened influenza vaccination policy decisions for older adults that have historically been undermined by the conclusions of observational studies.

A systematic review of interventions to promote work participation in older workers

PURPOSE

The objective of this systematic review was to synthesize evidence on the effectiveness of interventions aimed at promoting work participation in older workers.

METHODS

We followed a systematic review process developed by the Institute for Work & Health and a best evidence synthesis that ranked evidence as strong, moderate, limited, or insufficient.

RESULTS

Seven electronic databases were searched from inception to March 2014. Evidence from 14 studies were synthesized in 4 different intervention categories: multi-component, exercise, medication and other interventions. There was moderate evidence that work participation was improved by multi-component interventions encompassing at least two of three components (health service delivery, coordination of services, and work modifications). There was not enough evidence to recommend the other interventions.

CONCLUSIONS

Although there is a vast body of research on work participation of older workers, there are only a few high quality intervention studies aimed at improving work participation in this population. We recommend that multi-component interventions could be considered for implementation by practitioners to help improve work participation in older workers.

PRACTICAL APPLICATIONS

With a moderate level of evidence, multi-component interventions could be considered for use in practice if practitioners deem it suitable for their setting. There is not enough evidence to recommend exercise interventions, pharmaceutical interventions, different types of surgeries, patient education or work accommodation alone to improve work participation. However, the lack of evidence should not be considered, as absence of effect and practitioners should continue to be creative in developing solutions.

Recommended immunization schedules for adults: Clinical practice guidelines by the Escmid Vaccine Study Group (EVASG), European Geriatric Medicine Society (EUGMS) and the World Association for Infectious Diseases and Immunological Disorders (WAidid)

Rapid population aging has become a major challenge in the industrialized world and progressive aging is a key reason for making improvement in vaccination a cornerstone of public health strategy. An increase in age-related disorders and conditions is likely to be seen in the near future, and these are risk factors for the occurrence of a number of vaccine-preventable diseases. An improvement in infectious diseases prevention specifically aimed at adults and the elderly can therefore also decrease the burden of these chronic conditions by reducing morbidity, disability, hospital admissions, health costs, mortality rates and, perhaps most importantly, by improving the quality of life. Among adults, it is necessary to identify groups at increased risk of vaccine-preventable diseases and highlight the epidemiological impact and benefits of vaccinations using an evidence-based approach. This document provides clinical practice guidance on immunization for adults in order to provide recommendations for decision makers and healthcare workers in Europe. Although immunization is considered one of the most impactful and cost-effective public health measures that can be undertaken, vaccination coverage rates among adults are largely lower than the stated goal of ≥ 95% among adults, and stronger efforts are needed to increase coverage in this population. Active surveillance of adult vaccine-preventable diseases, determining the effectiveness of the vaccines approved for marketing in the last 5 y, the efficacy and safety of vaccines in immunocompromised patients, as well as in pregnant women, represent the priorities for future research.

Southern Hemisphere Influenza and Vaccine Effectiveness Research and Surveillance

The 2009 influenza A(H1N1)pdm09 pandemic highlighted the need for improved scientific knowledge to support better pandemic preparedness and seasonal influenza control. The Southern Hemisphere Influenza and Vaccine Effectiveness Research and Surveillance (SHIVERS) project, a 5-year (2012–2016) multiagency and multidisciplinary collaboration, aimed to measure disease burden, epidemiology, aetiology, risk factors, immunology, effectiveness of vaccination and other prevention strategies for influenza and other respiratory infectious diseases of public health importance. Two active, prospective, population-based surveillance systems were established for monitoring influenza and other respiratory pathogens among those hospitalized patients with acute respiratory illness and those enrolled patients seeking consultations at sentinel general practices. In 2015, a sero-epidemiological study will use a sample of patients from the same practices. These data will provide a full picture of the disease burden and risk factors from asymptomatic infections to severe hospitalized disease and deaths and related economic burden. The results during the first 2 years (2012–2013) provided scientific evidence to (a) support a change to NZ's vaccination policy for young children due to high influenza hospitalizations in these children; (b) contribute to the revision of the World Health Organization's case definition for severe acute respiratory illness for global influenza surveillance; and (c) contribute in part to vaccine strain selection using vaccine effectiveness assessment in the prevention of influenza-related consultations and hospitalizations. In summary, SHIVERS provides valuable international platforms for supporting seasonal influenza control and pandemic preparedness, and responding to other emerging/endemic respiratory-related infections.

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.

Estimating the Effect of Influenza Vaccination on Nursing Home Residents' Morbidity and Mortality

OBJECTIVES

To estimate the effect of influenza vaccination on hospitalization and mortality in nursing home (NH) residents.

DESIGN

Retrospective cohort study.

SETTING

Medicare claims data linked to NH Minimum Data Set assessments and Centers for Disease Control and Prevention (CDC) surveillance data from 122 U.S. cities.

PARTICIPANTS

More than 1 million Medicare fee-for-service, long-stay NH residents between 2000 and 2009.

MEASUREMENTS

Weekly facility outcome aggregates of NH resident pneumonia and influenza (P&I) hospitalizations and all-cause mortality and city-level P&I mortality as reported by the CDC were created. The seasonal vaccine match rate for influenza A/H1N1, A/H3N2, and B strains was calculated, and each outcome was compared in seasons of high and low match rates using facility fixed-effects regression models separately for full-year and nonsummer months.

RESULTS

Average weekly all-cause mortality varied across seasons from 3.74 to 4.13 per 1,000 NH residents per week, and hospitalization for P&I varied from 2.05 to 2.43. Vaccine match rates were invariably high for H1N1 but variable across seasons for the other two types. The association between vaccine match and reduction in overall mortality and P&I hospitalizations was strongest for A/H3N2, the influenza strain typically responsible for the most-severe influenza cases. Given the approximately 130,000 deaths and 77,000 P&I hospitalizations of long-stay NH residents during the 32 nonsummer weeks, the model estimated that a 50-percentage-point increase in the A/H3N2 match rate (from <25% to >75%) reduced long-stay NH resident deaths by 2.0% and P&I hospitalizations by 4.2%.

CONCLUSION

Well-matched influenza vaccine prevents P&I hospitalizations and mortality in NH residents.

Influenza vaccine effectiveness assessment through sentinel virological data in three post-pandemic seasons

Influenza vaccination aims at reducing the incidence of serious disease, complications and death among those with the most risk of severe influenza disease. Influenza vaccine effectiveness (VE) through sentinel surveillance data from the PIDIRAC program (Daily Acute Respiratory Infection Surveillance of Catalonia) during 2010-2011, 2011-2012, and 2012-2013 influenza seasons, with three different predominant circulating influenza virus (IV) types [A(H1N1)pdm09, A(H3N2) and B, respectively] was assessed. The total number of sentinel samples with known vaccination background collected during the study period was 3173, 14.7% of which had received the corresponding seasonal influenza vaccine. 1117 samples (35.2%) were positive for IV. A retrospective negative case control design was used to assess vaccine effectiveness (VE) for the entire period and for each epidemic influenza season. An overall VE of 58.1% (95% CI:46.8-67) was obtained. Differences in VE according to epidemic season were observed, being highest for the 2012-2013 season with predominance of IV type B (69.7% ;95% CI:51.5-81) and for the 2010-2011 season, with predominance of the A(H1N1)pdm09 influenza virus strain (67.2% ;95%CI:49.5-78.8) and lowest for the 2011-2012 season with A(H3N2) subtype predominance (34.2% ;95%CI:4.5-54.6). Influenza vaccination prevents a substantial number of influenza-associated illnesses. Although vaccines with increased effectiveness are needed and the search for a universal vaccine that is not subject to genetic modifications might increase VE, nowadays only the efforts to increase vaccination rates of high-risk population and healthcare personnel let reduce the burden of influenza and its complications.

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

Preinfluenza periods have been used to test for uncontrolled confounding in studies of influenza vaccine effectiveness, but some authors have claimed that confounding differs in preinfluenza and influenza periods. We tested this claim by comparing estimates of the vaccine-mortality association during the 2009/2010 influenza year, when there was essentially no circulation of seasonal influenza in the United States, and 2007/2008, a typical influenza year. We pooled data on seniors (adults aged ≥65 years) from 7 US managed care organizations that participated in the Vaccine Safety Datalink Project. We defined influenza vaccination, all-cause mortality, and potential confounders from administrative databases. We quantified the vaccine-mortality association using Cox regression. During 2007/2008, the adjusted hazard ratio was 0.44 prior to influenza season, 0.62 during influenza season, and 0.71 after influenza season. A similar pattern was observed during 2009/2010, when any effect of seasonal influenza vaccine observed during all time periods must have resulted from confounding: 0.65 during the autumn, 0.80 during the winter, and 0.84 during the summer. In a year with minimal seasonal influenza, we found no evidence that confounding in autumn preinfluenza periods is qualitatively different from confounding in winter. This supports the use of preinfluenza periods as control time periods in studies of influenza vaccine effectiveness.

Effectiveness of adjuvanted seasonal influenza vaccines (Inflexal V ® and Fluad ® ) in preventing hospitalization for influenza and pneumonia in the elderly: a matched case-control study

Annual vaccination is the main mean of preventing influenza in the elderly. In order to evaluate the effectiveness of the adjuvanted seasonal influenza vaccines available in Italy in preventing hospitalization for influenza and pneumonia, a matched case-control study was performed in elderly subjects during the 2010–2011 season in Genoa (Italy). Cases and controls were matched in a 1:1 ratio according to gender, age, socio-economic status and type of influenza vaccine. Vaccine effectiveness was calculated as IVE = [(1-OR)x100] and crude odds ratios were estimated through conditional logistic regression models. Adjusted odds ratios were estimated through multivariable logistic models.

In the study area, influenza activity was moderate in the 2010–2011 season, with optimal matching between circulating viruses and vaccine strains. We recruited 187 case-control pairs; 46.5% of cases and 79.1% of controls had been vaccinated. The adjuvanted influenza vaccines (Fluad^® considered together with Inflexal V^®) were associated with a significant reduction in the risk of hospitalization, their effectiveness being 94.8% (CI 77.1–98.8). Adjusted vaccine effectiveness was 95.2% (CI 62.8–99.4) and 87.8 (CI 0.0–98.9) for Inflexal V^® and Fluad^®, respectively. Both adjuvanted vaccines proved effective, although the results displayed statistical significance only for Inflexal V^® (p = 0.004), while for Fluad^® statistical significance was not reached (p = 0.09). Our study is the first to provide information on the effectiveness of Inflexal V^® in terms of reducing hospitalizations for influenza or pneumonia in the elderly, and demonstrates that this vaccine yields a high degree of protection and that its use would generate considerable saving for the National Health Service.

Pneumonia immunization in older adults: review of vaccine effectiveness and strategies

Vaccination remains the primary preventive strategy in the elderly against Streptococcus pneumoniae and influenza infections. The effectiveness of this strategy in preventing pneumonia has been in doubt despite the increase in vaccination coverage among older adults. Randomized controlled trials (RCTs) and observational studies aimed at determining clinical outcomes and immune response following pneumococcal vaccination have yielded conflicting results. The protective efficacy of pneumococcal vaccination against pneumonia in older adults has not been firmly established due to a lack of RCTs specifically examining patients ≥ 65 years of age. Similarly, the reported benefits of influenza vaccination have been derived from observational data. The assessment of clinical benefit from influenza vaccination in the elderly population is complicated by varying cohorts, virulence of the influenza strain, and matching of vaccine and circulating viral strains. The presence of selection bias and use of nonspecific end points in these studies make the current evidence inconclusive in terms of overall benefit. The development of more immunogenic vaccines through new formulations or addition of adjuvants holds the promise of revolutionizing delivery and improving efficacy. Dismantling existing barriers through education, providing technology assistance predominantly to developing countries, and establishing clear regulatory guidance on pathways for approval are necessary to ensure timely production and equitable distribution.

Effectiveness of adjuvanted influenza vaccination in elderly subjects in northern Italy

Although vaccination against influenza is recommended for elderly and high-risk patients in many countries, efficacy in the elderly has been suboptimal. The MF59 adjuvanted trivalent inactivated vaccine (ATIV) was developed to increase the immune response of elderly subjects to influenza vaccination, but its effectiveness has not yet been well documented. This prospective, observational study evaluated the relative effectiveness of ATIV versus nonadjuvanted trivalent inactivated vaccine (TIV) in individuals at least 65 years of age in Lombardy, northern Italy. Hospitalizations for influenza or pneumonia (International Classification of Diseases, Ninth Revision, Clinical Modification, codes 480–487) during the 2006–2007, 2007–2008, and 2008–2009 influenza seasons were identified from administrative databases. Stratified and regression analyses, including the propensity score to adjust for confounding, as well as generalized estimating equations to account for repeated vaccination, were used. Overall, 107,661 records were evaluated, contributing 170,988 person-seasons of observation. Since ATIV is preferentially recommended for more frail individuals, subjects vaccinated with ATIV were older and had more functional impairment and comorbidities. In the primary analysis, risk of hospitalization for influenza or pneumonia was 25% lower for ATIV relative to TIV (relative risk = 0.75, 95% confidence interval: 0.57, 0.98). To the extent that there is residual bias, ATIV is likely to be even more protective than this result suggests.

[Vaccination against seasonal influenza in France in 2010 and 2011: decrease of coverage rates and associated factors]

AIM

To measure the seasonal influenza vaccination coverage rate (VCR) in France in 2010, one year after the A(H1N1) influenza pandemic, and 2011 by age and target disease and to identify risk factors associated with a lack of vaccination in 2010 for those previously vaccinated in 2009.

METHODS

At the beginning of each vaccination campaign, the National Health Insurance, covering 86% of the French population, sends free influenza vaccination vouchers to at-risk beneficiaries aged under 65 suffering from diverse target diseases and to all individuals aged 65 and over (around 11.5 million).

RESULTS

The global VCR (50.4%), except people with asthma identified by drug refunds, decreased in 2010 compared with the previous three years when it was close to 60% (51.0% in 2011). For people under 65 years old, it fell from 40.3% in 2009 to 31.6% in 2010 (33.1% in 2011) and those aged 65 years and over from 63.3% to 53.8% (54.0% in 2011). The VCR of each target disease also decreased, especially for asthma, but not for HIV infection with campaign modification in 2010. It decreased among those aged 65 years and over with target disease (72.3% in 2009, 60.4% in 2010, 60.7% in 2011). Vaccination lack in 2010 was found to be associated with younger age, low number of drug deliveries and consultations with a general practitioner or a specialist, hospitalisation and the residence in a region of South of France or in overseas regions.

CONCLUSION

An important decline of the VCR was observed in France since 2010 while the recommended VCR is 75%. Efforts must be led to improve the confidence of the insurant, especially towards the most fragile groups.

Evaluation of influenza virus A/H3N2 and B vaccines on the basis of cross-reactivity of postvaccination human serum antibodies against influenza viruses A/H3N2 and B isolated in MDCK cells and embryonated hen eggs

The vaccine strains against influenza virus A/H3N2 for the 2010-2011 season and influenza virus B for the 2009-2010 and 2010-2011 seasons in Japan are a high-growth reassortant A/Victoria/210/2009 (X-187) strain and an egg-adapted B/Brisbane/60/2008 (Victoria lineage) strain, respectively. Hemagglutination inhibition (HI) tests with postinfection ferret antisera indicated that the antisera raised against the X-187 and egg-adapted B/Brisbane/60/2008 vaccine production strains poorly inhibited recent epidemic isolates of MDCK-grown A/H3N2 and B/Victoria lineage viruses, respectively. The low reactivity of the ferret antisera may be attributable to changes in the hemagglutinin (HA) protein of production strains during egg adaptation. To evaluate the efficacy of A/H3N2 and B vaccines, the cross-reactivities of postvaccination human serum antibodies against A/H3N2 and B/Victoria lineage epidemic isolates were assessed by a comparison of the geometric mean titers (GMTs) of HI and neutralization (NT) tests. Serum antibodies elicited by the X-187 vaccine had low cross-reactivity to both MDCK- and egg-grown A/H3N2 isolates by HI test and narrow cross-reactivity by NT test in all age groups. On the other hand, the GMTs to B viruses detected by HI test were below the marginal level, so the cross-reactivity was assessed by NT test. The serum neutralizing antibodies elicited by the B/Brisbane/60/2008 vaccine reacted well with egg-grown B viruses but exhibited remarkably low reactivity to MDCK-grown B viruses. The results of these human serological studies suggest that the influenza A/H3N2 vaccine for the 2010-2011 season and B vaccine for the 2009-2010 and 2010-2011 seasons may possess insufficient efficacy and low efficacy, respectively.

Effectiveness of influenza vaccine in aging and older adults: comprehensive analysis of the evidence

Foremost amongst the diseases preventable by vaccination is influenza. Worldwide, influenza virus infection is associated with serious adverse events leading to hospitalization, debilitating complications, and death in elderly individuals. Immunization is considered to be the cornerstone for preventing these adverse health outcomes, and vaccination programs are timed to optimize protection during the annual influenza season. Trivalent inactivated influenza virus vaccines are believed to be both effective and cost-saving; however, in spite of widespread influenza vaccination programs, rates of hospitalization for acute respiratory illness and cardiovascular diseases have been increasing in this population during recent annual influenza seasons. From meta-analyses summarizing estimates of influenza vaccine effectiveness from available observational clinical studies, this review aims to examine how effective current influenza vaccine strategies are in the aging and older adult population and to analyze which are the most important biases that interfere with measurements of influenza vaccine effectiveness. Furthermore, consideration is given to strategies that should be adopted in order to optimize influenza vaccine effectiveness in the face of immune exhaustion.

The unmet need in the elderly: how immunosenescence, CMV infection, co-morbidities and frailty are a challenge for the development of more effective influenza vaccines

Influenza remains the single most important cause of excess disability and mortality during the winter months. In spite of widespread influenza vaccination programs leading to demonstrated cost-savings in the over 65 population, hospitalization and death rates for acute respiratory illnesses continue to rise. As a person ages, increased serum levels of inflammatory cytokines are commonly recorded (TNF-α, IL-1, IL-6). Termed "inflammaging", this has been linked to persistent cytomegalovirus (CMV) infection and immune senescence, while increased anti-inflammatory cytokines (IL-10, TGF-β) are possibly associated with more healthy aging. Paradoxically, a shift with aging toward an anti-inflammatory (IL-10) response and decline in the IFN-γ:IL-10 ratio in influenza-challenged peripheral blood mononuclear cells is associated with a decline in the cytolytic capacity of CD8+ T cells responsible for clearing influenza virus from infected lung tissue. Thus, it is seemingly counter intuitive that the immune phenotype of healthy aging predicts a poor cell-mediated immune response and more serious outcomes of influenza. Herein we postulate a mechanistic link between the accumulation of late-stage, potentially terminally differentiated T cells, many or most of which result from CMV infection, and the immunopathogenesis of influenza infection, mediated by granzyme B in older adults. Further, adjuvanted influenza vaccines that stimulate inflammatory cytokines and suppress the IL-10 response to influenza challenge, would be expected to enhance protection in the 65+ population.

Association between use of statins and mortality among patients hospitalized with laboratory-confirmed influenza virus infections: a multistate study

BACKGROUND

Statins may have anti-inflammatory and immunomodulatory effects that could reduce the risk of mortality from influenza virus infections.

METHODS

The Centers for Disease Control and Prevention's Emerging Infections Program conducts active surveillance for persons hospitalized with laboratory-confirmed influenza in 59 counties in 10 states. We analyzed data for hospitalized adults during the 2007-2008 influenza season to evaluate the association between receiving statins and influenza-related death.

RESULTS

We identified 3043 patients hospitalized with laboratory-confirmed influenza, of whom 1013 (33.3%) received statins and 151 (5.0%) died within 30 days of their influenza test. Patients who received statins were more likely to be older, male, and white; to suffer from cardiovascular, metabolic, renal, and chronic lung disease; and to have been vaccinated against influenza that season. In a multivariable logistic regression model, administration of statins prior to or during hospitalization was associated with a protective odds of death (adjusted odds ratio, 0.59 [95% confidence interval, .38-.92]) when adjusting for age; race; cardiovascular, lung, and renal disease; influenza vaccination; and antiviral administration.

CONCLUSIONS

Statin use may be associated with reduced mortality in patients hospitalized with influenza.

Effectiveness of the Brazilian influenza vaccination policy, a systematic review

Since 1999, Brazil has undertaken annual influenza vaccine campaigns, free of charge, targeting the elderly population, health professionals, and immune-deficient patients. We conducted a systematic review of literature in order to evaluate the effectiveness of the initiative. We used the keywords influenza, vaccine, Brazil and effectiveness to search the main databases. Thirty-one studies matched our inclusion and exclusion criteria. Influenza vaccine coverage among the elderly is high, though not as high as suggested by the official figures. Estimates on effectiveness are scarce. The majority come from ecological studies that show a modest reduction in mortality and hospital admissions due to influenza-related causes. Such reduction is not evident in the North and Northeastern states of Brazil, a finding that is probably related to the different seasonal pattern of influenza in equatorial and tropical regions. Brazilian epidemiologists still owe society better-designed studies addressing the effectiveness of influenza vaccine campaigns.

New approaches for influenza vaccination of healthcare workers

PURPOSE OF REVIEW

Vaccination of healthcare workers (HCWs) against influenza is an important component of infection control in healthcare settings but HCW vaccination rates remain low. Here we review current and emerging strategies for influenza vaccination of HCWs.

RECENT FINDINGS

Professional organizations have recommended annual influenza vaccination for HCWs since 1984, but HCW vaccination rates have improved minimally. Recent studies indicate that comprehensive influenza vaccination programs have failed to achieve adequate influenza vaccination rates for HCWs in spite of allocating substantial resources to HCW vaccination programs. Mandatory HCW influenza vaccination programs have been introduced and clearly outperform traditional comprehensive vaccination programs. Some argue that mandatory vaccination programs infringe on HCW autonomy, and introduction of mandatory vaccination programs can be controversial. Public reporting of institutional HCW influenza vaccination rates is another strategy to achieve high vaccination rates, as HCW influenza vaccination may be used in the future as a quality and safety metric.

SUMMARY

HCW influenza vaccination in the setting of a comprehensive infection control program is a core patient-safety practice. Mandatory HCW influenza vaccination and public reporting of HCW vaccination rates will complement one another in achieving substantial gains for HCW influenza vaccination programs.

Frailty is associated with impairment of vaccine-induced antibody response and increase in post-vaccination influenza infection in community-dwelling older adults

Annual immunization with a trivalent inactivated vaccine (TIV) is considered efficacious for prevention of seasonal influenza in older adults. However, significant controversy exists in the current literature regarding the clinical effectiveness of TIV immunization in this highly heterogeneous population. Frailty is an important geriatric syndrome characterized by decreased physiologic reserve and increased vulnerability to stressors. Using a validated set of frailty criteria, we conducted a prospective observational study to evaluate TIV-induced strain-specific hemagglutination inhibition (HI) antibody titers and post-vaccination rates of influenza-like illness (ILI) and infection in frail and nonfrail older adults. The results indicate that frailty was associated with significant impairment in TIV-induced strain-specific HI titers and increased rates of ILI and laboratory-confirmed influenza infection. These findings suggest that assessing frailty status in the elderly may identify those who are less likely to respond to TIV immunization and be at higher risk for seasonal influenza and its complications.

Vaccine effectiveness in older individuals: what has been learned from the influenza-vaccine experience

Vaccination policies in most high-income countries attempt to reduce the adverse impact of influenza targeting people aged at least 60 years. However, while it is widely believed that the current immunization strategy saves many lives, influenza infection still remains a severe burden in aged individuals leading to a wide debate on the exact magnitude of the benefit of vaccination in this population. The first aim of the present review is to examine how effective current influenza-vaccine strategies are in aged adults, by analysing which are the most important factors modulating the interpretation of study results in this population. Furthermore, consideration will be given to how immune factors influence the measurement of vaccine efficacy/effectiveness, where advancing age leads to deleterious changes in the adaptive immune system, resulting in less than optimal responses to infectious agents and vaccination. Finally this review concludes with possible strategies to improve the ability of the senescent immune system to respond to vaccination.

Influenza vaccine responses in older adults

The most profound consequences of immune senescence with respect to public health are the increased susceptibility to influenza and loss of efficacy of the current split-virus influenza vaccines in older adults, which are otherwise very effective in younger populations. Influenza infection is associated with high rates of complicated illness including pneumonia, heart attacks and strokes in the 65+ population. Changes in both innate and adaptive immune function not only converge in the reduced response to vaccination and protection against influenza, but present significant challenges to new vaccine development. In older adults, the goal of vaccination is more realistically targeted to providing clinical protection against disease rather sterilizing immunity. Correlates of clinical protection may not be measured using standard techniques such as antibody titres to predict vaccine efficacy. Further, antibody responses to vaccination as a correlate of protection may fail to detect important changes in cellular immunity and enhanced vaccine-mediated protection against influenza illness in older people. This article will discuss the impact of influenza in older adults, immunologic targets for improved efficacy of the vaccines, and alternative correlates of clinical protection against influenza that are needed for more effective translation of novel vaccination strategies to improved protection against influenza in older adults.

Seasonal influenza vaccination coverage in France during two influenza seasons (2007 and 2008) and during a context of pandemic influenza A(H1N1) in 2009

OBJECTIVES

To measure the seasonal influenza vaccination coverage rate (VCR) in France in 2009, year of the A(H1N1) influenza pandemic, by age and target disease and compare it with the VCR for the 2007 and 2008 influenza seasons.

METHOD

At the beginning of each annual seasonal vaccination campaign, the National Health Insurance, covering 86% of the French population, sends free influenza vaccination vouchers to at-risk beneficiaries aged under 65 suffering from diverse chronic diseases and to all individuals aged 65 and over (around 11 million). Vaccination is estimated from refund claims registered in the National Health Insurance Information System.

RESULTS

The global VCR for the target population was 51% in 2007, 55.8% in 2008 and 56.9% in 2009. In 2009, the VCR for children under 10 years old was 24.3%, 28.1% in the 10-19 age range, 39.2% in the 20-64 age range and 63.3% for individuals aged 65 and over, of which 72.3% with a targeted chronic disease and 56.9% without. The inclusion of asthma as a target disease, lowered the global VCR for children under 10 years old (30.6% without asthma) but VCR increased proportionally with the number of annual refunds for drugs against asthma and chronic obstructive pulmonary disease. The 2009 vaccine uptake rates in target group children, adolescents, young adults and to a lesser extent the population aged 65 and over suffering from a chronic disease (particularly chronic respiratory disease), could have been positively impacted by the A(H1N1) influenza context.

CONCLUSION

The influenza VCR varies considerably according to age and target disease but globally remains inferior to the recommended 75% coverage rate. These results permit the detailed analysis of VCR distribution by disease and target group and highlights areas for reflection and action. Specific studies should be conducted in order to understand why the VCR is lower in certain target groups.

Efficacy studies of influenza vaccines: effect of end points used and characteristics of vaccine failures

BACKGROUND

End points used to detect influenza in vaccine efficacy trials have varied. Both the inactivated and live attenuated influenza vaccines are efficacious; however, failure to protect occurs.

METHODS

We compared characteristics of influenza A (H3N2) and B cases from 3 years of a comparative placebo-controlled trial of inactivated and live attenuated vaccines, and we evaluated the laboratory end points used to determine efficacy.

RESULTS

Although illness duration and reported symptoms did not differ by intervention, subjects with influenza in the inactivated vaccine group were less likely than those in the placebo group to report medically attended illnesses. All influenza type A (H3N2) and B cases isolated in cell culture were also identified by real-time polymerase chain reaction (rtPCR). However, only 69% of type A (H3N2) cases identified by rtPCR also were isolated in cell culture. Isolation frequency was lowest among live attenuated vaccine failures, a reflection of lower specimen viral loads. Among cases of rtPCR identified influenza A (H3N2), 90% of placebo and 87% of live attenuated vaccine recipients but only 23% of inactivated vaccine recipients demonstrated serologic confirmation of infection.

CONCLUSIONS

In influenza vaccine efficacy studies, virus identification using rtPCR is the ideal end point. Isolation in cell culture will miss cases, and a serologic end point alone will overestimate inactivated vaccine efficacy.

Influenza vaccination and all-cause mortality in community-dwelling elderly in Ontario, Canada, a cohort study

The objective of this study was to evaluate the effectiveness of influenza vaccines in reducing all-cause mortality among community-dwelling elderly. We included 25,922 Ontario residents over age 65 who responded to population health surveys. After full adjustment, influenza vaccination was associated with a statistically significant reduction in all-cause mortality during influenza seasons (hazard ratio (HR)=0.61; 95% CI 0.47-0.79). Contrary to expectations, statistically significant associations between influenza vaccination and mortality were also observed during periods preceding (HR=0.55; 95% CI 0.40-0.75) and following (HR=0.74; 95% CI 0.59-0.94) influenza seasons, indicating the presence of residual confounding. Adjustment for functional status indicators, excluding individuals with high one-year predicted mortality at baseline, and moving the start date of follow-up failed to eliminate the refractory confounding. Since observational studies are prone to bias, future efforts to estimate vaccine effectiveness in the elderly should strive to minimize bias through improved data quality, novel data sources, and/or new analytical techniques.

Influenza vaccines provide diminished protection but are cost-saving in older adults

Influenza is associated with substantial morbidity and mortality in adults aged over 65 years. Although vaccination remains the most effective method of preventing influenza and its sequellae, current vaccination strategies provide less protection to older adults than to younger persons. Influenza vaccination in community-dwelling older adults is cost-effective, though there is room for improvement. Newer vaccine strategies considered for use in older adults include alternate routes of administration (intradermal or intranasal), addition of adjuvant, and novel methods of antigen presentation. Measuring cell-mediated immune response to new vaccines in addition to antibody response may correlate better with vaccine efficacy in this population. Whilst pandemic influenza A/H1N1 2009 (pH1N1) has largely spared older adults, the impact of pH1N1 vaccination has yet to be determined.