Effectiveness of trivalent and monovalent influenza vaccines against laboratory-confirmed influenza infection in persons with medically attended influenza-like illness in Bavaria, Germany, 2010/2011 season

Cost-Effectiveness of Influenza Vaccination Strategies in Adults: Older Adults Aged ≥65 Years, Adults Aged 50–64 Years, and At-Risk Adults Aged 19–64 Years

The high disease burden of influenza in elderly and chronically ill adults may be due to the suboptimal effectiveness and mismatch of the conventional trivalent influenza vaccine (TIV). This study evaluated the cost-effectiveness of quadrivalent (QIV), adjuvanted trivalent (ATIV), and high-dose quadrivalent (HD-QIV) vaccines versus TIV used under the current Korean National Immunization Program (NIP) in older adults aged ≥65 years. We also evaluated the cost-effectiveness of programs for at-risk adults aged 19–64 and adults aged 50–64. A one-year static population model was used to compare the costs and outcomes of alternative vaccination programs in each targeted group. Influenza-related parameters were derived from the National Health Insurance System claims database; other inputs were extracted from the published literature. Incremental cost-effectiveness ratios (ICERs) were assessed from a societal perspective. In the base case analysis (older adults aged ≥65 years), HD-QIV was superior, with the lowest cost and highest utility. Compared with TIV, ATIV was cost-effective (ICER $34,314/quality-adjusted life-year [QALY]), and QIV was not cost-effective (ICER $46,486/QALY). The cost-effectiveness of HD-QIV was robust for all parameters except for vaccine cost. The introduction of the influenza NIP was cost-effective or even cost-saving for the remaining targeted gr3oups, regardless of TIV or QIV.

Decline in Seasonal Influenza Vaccine Effectiveness With Vaccination Program Maturation: A Systematic Review and Meta-analysis

BACKGROUND

Evidence suggests that repeated influenza vaccination may reduce vaccine effectiveness (VE). Using influenza vaccination program maturation (PM; number of years since program inception) as a proxy for population-level repeated vaccination, we assessed the impact on pooled adjusted end-season VE estimates from outpatient test-negative design studies.

METHODS

We systematically searched and selected full-text publications from January 2011 to February 2020 (PROSPERO: CRD42017064595). We obtained influenza vaccination program inception year for each country and calculated PM as the difference between the year of deployment and year of program inception. We categorized PM into halves (cut at the median), tertiles, and quartiles and calculated pooled VE using an inverse-variance random-effects model. The primary outcome was pooled VE against all influenza.

RESULTS

We included 72 articles from 11 931 citations. Across the 3 categorizations of PM, a lower pooled VE against all influenza for all patients was observed with PM. Substantially higher reductions were observed in older adults (≥65 years). We observed similar results for A(H1N1)pdm09, A(H3N2), and influenza B.

CONCLUSIONS

The evidence suggests that influenza VE declines with vaccination PM. This study forms the basis for further discussions and examinations of the potential impact of vaccination PM on seasonal VE.

Variable seasonal influenza vaccine effectiveness across geographical regions, age groups and levels of vaccine antigenic similarity with circulating virus strains: A systematic review and meta-analysis of the evidence from test-negative design studies after the 2009/10 influenza pandemic

BACKGROUND

We examined the influence of some factors on seasonal influenza vaccine effectiveness (VE) from test-negative design (TND) studies.

METHODS

We systematically searched for full-text publications of VE against laboratory-confirmed influenza from TND studies in outpatient settings after the 2009/10 influenza pandemic. Two reviewers independently selected and extracted data from the included studies. We calculated pooled adjusted VE across geographical regions, age groups and levels of vaccine antigenic similarity with circulating virus strains, using an inverse variance, random-effects model.

RESULTS

We included 76 full-text articles from 11,931 citations. VE estimates against A(H1N1)pdm09, A(H3N2), influenza B, and all influenza were homogenous and point pooled VE higher in the Southern hemisphere compared with the Northern hemisphere. The difference in pooled VE between the Southern and Northern hemispheres was statistically significant for A(H3N2), influenza B, and all influenza. A consistent pattern was observed in pooled VE across both hemispheres and continents, with the highest point pooled VE being against A(H1N1)pdm09, followed by influenza B, and lowest against A(H3N2). A nearly consistent pattern was observed in pooled VE across age groups in the Northern hemisphere, with pooled VE mostly decreasing with age. Point pooled VE against A(H3N2), influenza B, and all influenza were statistically significantly higher when vaccine was antigenically similar to circulating virus strains compared with when antigenically dissimilar. Similar pattern was observed in the Northern hemisphere, but there was a lack of data from the Southern hemisphere.

CONCLUSION

Consistent patterns appear to exist in seasonal influenza VE across regions, age groups, and levels of vaccine antigenic similarity with circulating virus strains, with best vaccine performance against A(H1N1)pdm09 and worst against A(H3N2). The evidence highlights the need to consider geographical location, age, and vaccine antigenic similarity with circulating virus strains when designing and evaluating influenza VE studies.

Variations in Seasonal Influenza Vaccine Effectiveness due to Study Characteristics: A Systematic Review and Meta-analysis of Test-Negative Design Studies

BACKGROUND

Study characteristics influence vaccine effectiveness (VE) estimation. We examined the influence of some of these on seasonal influenza VE estimates from test-negative design (TND) studies.

METHODS

We systematically searched bibliographic databases and websites for full-text publications of TND studies on VE against laboratory-confirmed seasonal influenza in outpatients after the 2009 pandemic influenza. We followed the Cochrane Handbook for Systematic Reviews of Interventions guidelines. We examined influence of source of vaccination information, respiratory specimen swab time, and covariate adjustment on VE. We calculated pooled adjusted VE against H1N1 and H3N2 influenza subtypes, influenza B, and all influenza using an inverse-variance random-effects model.

RESULTS

We included 70 full-text articles. Pooled VE against H1N1 and H3N2 influenza subtypes, influenza B, and all influenza was higher for studies that used self-reported vaccination than for those that used medical records. Pooled VE was higher with respiratory specimen collection within ≤7 days vs ≤4 days of symptom onset, but the opposite was observed for H1N1. Pooled VE was higher for studies that adjusted for age but not for medical conditions compared with those that adjusted for both. There was, however, a lack of statistical significance in almost all differences in pooled VE between compared groups.

CONCLUSIONS

The available evidence is not strong enough to conclude that influenza VE from TND studies varies by source of vaccination information, respiratory specimen swab time, or adjustment for age/medical conditions. The evidence is, however, indicative that these factors ought to be considered while designing or evaluating TND studies of influenza VE.

The Use of Test-negative Controls to Monitor Vaccine Effectiveness: A Systematic Review of Methodology

BACKGROUND

The test-negative design is an increasingly popular approach for estimating vaccine effectiveness (VE) due to its efficiency. This review aims to examine published test-negative design studies of VE and to explore similarities and differences in methodological choices for different diseases and vaccines.

METHODS

We conducted a systematic search on PubMed, Web of Science, and Medline, for studies reporting the effectiveness of any vaccines using a test-negative design. We screened titles and abstracts and reviewed full texts to identify relevant articles. We created a standardized form for each included article to extract information on the pathogen of interest, vaccine(s) being evaluated, study setting, clinical case definition, choices of cases and controls, and statistical approaches used to estimate VE.

RESULTS

We identified a total of 348 articles, including studies on VE against influenza virus (n = 253), rotavirus (n = 48), pneumococcus (n = 24), and nine other pathogens. Clinical case definitions used to enroll patients were similar by pathogens of interest but the sets of symptoms that defined them varied substantially. Controls could be those testing negative for the pathogen of interest, those testing positive for nonvaccine type of the pathogen of interest, or a subset of those testing positive for alternative pathogens. Most studies controlled for age, calendar time, and comorbidities.

CONCLUSIONS

Our review highlights similarities and differences in the application of the test-negative design that deserve further examination. If vaccination reduces disease severity in breakthrough infections, particular care must be taken in interpreting vaccine effectiveness estimates from test-negative design studies.

The burden of severe cases of Influenza disease: the Friuli Venezia Giulia Region experience

INTRODUCTION

Influenza is a matter of serious concern for clinicians, in both outpatient and in-hospital settings. Worldwide, the 2017-18 epidemic proved to be the most severe since 2003-04. We report a real-world experience regarding the management of patients with influenza admitted to a large teaching hospital in the Friuli Venezia Giulia region during the 2017-2018 influenza season. We also provide a practical guide for the management of hospitalized influenza patients.

METHODS

A retrospective observational analysis was conducted among all influenza patients requiring admission to our center during the 2017-18 season.

RESULTS

Overall, 29 patients were admitted to the University Hospital of Udine during the 2017-18 season with a diagnosis of influenza. B virus was responsible for the majority of cases. More than 65.5% of the subjects presented with a complication. We estimated that 41.4% of the patients admitted were affected by a "severe form". All these cases required admission to the Intensive Care Unit, with 27.6% and 10.3% needing Orotracheal Intubation and Extracorporeal Membrane Oxygenation, respectively. The fatality rate was 24.1%. Notably, only 9 subjects in our cohort had been vaccinated. Based on the experience acquired during the past season, we propose a practical guide to the management of influenza cases in everyday hospital practice.

CONCLUSION

The cornerstones of the management of all hospitalized influenza patients are the rapid identification and treatment of severe forms. Timely and strict adherence to contact and respiratory precautions are also fundamental to reducing the risk of intra-hospital outbreaks. Despite improvements in antiviral therapies and supportive measures, influenza-related morbidity and mortality remain high. In our opinion, a universal vaccination program is the only safe and effective method of filling the gap.

Vaccine effectiveness against laboratory-confirmed influenza hospitalizations among young children during the 2010-11 to 2013-14 influenza seasons in Ontario, Canada

Uncertainty remains regarding the magnitude of effectiveness of influenza vaccines for preventing serious outcomes, especially among young children. We estimated vaccine effectiveness (VE) against laboratory-confirmed influenza hospitalizations among children aged 6-59 months. We used the test-negative design in hospitalized children in Ontario, Canada during the 2010-11 to 2013-14 influenza seasons. We used logistic regression models adjusted for age, season, and time within season to calculate VE estimates by vaccination status (full vs. partial), age group, and influenza season. We also assessed VE incorporating prior history of influenza vaccination. We included specimens from 9,982 patient hospitalization episodes over four seasons, with 12.8% testing positive for influenza. We observed variation in VE by vaccination status, age group, and influenza season. For the four seasons combined, VE was 60% (95%CI, 44%-72%) for full vaccination and 39% (95%CI, 17%-56%) for partial vaccination. VE for full vaccination was 67% (95%CI, 48%-79%) for children aged 24-59 months, 48% (95%CI, 12%-69%) for children aged 6-23 months, 77% (95%CI, 47%-90%) for 2010-11, 59% (95%CI, 13%-81%) for 2011-12, 33% (95%CI, -18% to 62%) for 2012-13, and 72% (95%CI, 42%-86%) for 2013-14. VE in children aged 24-59 months appeared similar between those vaccinated in both the current and previous seasons and those vaccinated in the current season only, with the exception of 2012-13, when VE was lower for those vaccinated in the current season only. Influenza vaccination is effective in preventing pediatric laboratory-confirmed influenza hospitalizations during most seasons.

Effect of Repeated Vaccination With the Same Vaccine Component Against 2009 Pandemic Influenza A(H1N1) Virus

Background

The 2009 pandemic influenza A(H1N1) (A[H1N1]pdm09) vaccine component has remained unchanged from 2009. We estimate the effectiveness of current and prior inactivated influenza A(H1N1)pdm09 vaccination from influenza seasons 2010-2011 to 2015-2016.

Methods

Patients attended with influenza-like illness were tested for influenza. Four periods with continued A(H1N1)pdm09 circulation were included in a test-negative design.

Results

We enrolled 1278 cases and 2343 controls. As compared to individuals never vaccinated against influenza A(H1N1)pdm09, the highest effectiveness (66%; 95% confidence interval, 49%-78%) was observed in those vaccinated in the current season who had received 1-2 prior doses. The effectiveness was not statistically lower in individuals vaccinated in the current season only (52%) or in those without current vaccination and >2 prior doses (47%). However, the protection was lower in individuals vaccinated in the current season after >2 prior doses (38%; P = .009) or those currently unvaccinated with 1-2 prior doses (10%; P < .001). Current-season vaccination improved the effect in individuals with 1-2 prior doses and did not modify significantly the risk of influenza in individuals with >2 prior doses.

Conclusion

Current vaccination or several prior doses were needed for high protection. Despite the decreasing effect of repeated vaccination, current-season vaccination was not inferior to no current-season vaccination.

Effectiveness of seasonal influenza vaccination in community-dwelling elderly people: an individual participant data meta-analysis of test-negative design case-control studies

BACKGROUND

Several aggregate data meta-analyses have provided estimates of the effectiveness of influenza vaccination in community-dwelling elderly people. However, these studies ignored the effects of patient-level confounders such as sex, age, and chronic diseases that could bias effectiveness estimates. We aimed to assess the confounder-adjusted effectiveness of influenza vaccines on laboratory-confirmed influenza among elderly people by conducting a global individual participant data meta-analysis.

METHODS

In this individual participant data meta-analysis, we considered studies included in a previously conducted aggregate data meta-analysis that included test-negative design case-control studies published up to July 13, 2014. We contacted all authors of the included studies on Dec 1, 2014, to request individual participant data. Patients were excluded if their unique identifier was missing, their vaccination status was unknown, their outcome status was unknown, or they had had suspected influenza infection more than once in the same influenza season. Cases were patients with influenza-like illness symptoms who tested positive for at least one of A H1N1, A H1N1 pdm09, A H3N2, or B viruses; controls were patients with influenza-like illness symptoms who tested negative for these virus types or subtypes. Influenza vaccine effectiveness against overall and subtype-specific laboratory-confirmed influenza were the primary and secondary outcomes. We used a generalised linear mixed model to calculate adjusted vaccine effectiveness according to vaccine match to the circulating strains of influenza virus and intensity of the virus activity (epidemic or non-epidemic). Vaccine effectiveness was defined as the relative reduction in risk of laboratory-confirmed influenza in vaccinated patients compared with unvaccinated patients. We did subgroup analyses to estimate vaccine effectiveness according to hemisphere, age category, and health status.

FINDINGS

We received 23 of the 53 datasets included in the aggregate data meta-analysis. Furthermore, six additional datasets were provided by data collaborators, which resulted in individual participant data for a total of 5210 participants. A total of 4975 patients had the required data for analysis. Of these, 3146 (63%) were controls and 1829 (37%) were cases. Influenza vaccination was significantly effective during epidemic seasons irrespective of vaccine match status (matched adjusted vaccine effectiveness 44·38%, 95% CI 22·63-60·01; mismatched adjusted vaccine effectiveness 20·00%, 95% CI 3·46-33·68; analyses in the imputed dataset). Seasonal influenza vaccination did not show significant effectiveness during non-epidemic seasons. We found substantial variation in vaccine effectiveness across virus types and subtypes, with the highest estimate for A H1N1 pdm09 (53·19%, 10·25-75·58) and the lowest estimate for B virus types (-1·52%, -39·58 to 26·16). Although we observed no significant differences between subgroups in each category (hemisphere, age, and health status), influenza vaccination showed a protective effect among elderly people with cardiovascular disease, lung disease, or aged 75 years and younger.

INTERPRETATION

Influenza vaccination is moderately effective against laboratory-confirmed influenza in elderly people during epidemic seasons. More research is needed to investigate factors affecting vaccine protection (eg, brand-specific or type-specific vaccine effectiveness and repeated annual vaccination) in elderly people.

FUNDING

University Medical Center Groningen.

Case-Control Study of Vaccine Effectiveness in Preventing Laboratory-Confirmed Influenza Hospitalizations in Older Adults, United States, 2010-2011

BACKGROUND

 Older adults are at increased risk of influenza-associated complications, including hospitalization, but influenza vaccine effectiveness (VE) data are limited for this population. We conducted a case-control study to estimate VE to prevent laboratory-confirmed influenza hospitalizations among adults aged ≥50 years in 11 US Emerging Infections Program hospitalization surveillance sites.

METHODS

 Cases were influenza infections (confirmed by reverse-transcription polymerase chain reaction) in adults aged ≥50 years hospitalized during the 2010-2011 influenza season, identified through Emerging Infections Program surveillance. Community controls, identified through home telephone lists, were matched by age group (±5 years), county, and month of hospitalization for case patients. Vaccination status was determined by self-report (with location and date) or medical records. Conditional logistic regression models were used to calculate adjusted VE (aVE) estimates (100 × [1 - adjusted odds ratio]), adjusting for sex, race, socioeconomic factors, smoking, chronic medical conditions, recent hospitalization for a respiratory condition, and functional status.

RESULTS

 Among case patients, 205 of 368 (55%) were vaccinated, compared with 489 of 773 controls (63%). Case patients were more likely to be of nonwhite race and more likely to have ≥2 chronic health conditions, a recent hospitalization for a respiratory condition, an income <$35 000, and a lower functional status score (P < .01 for all). The aVE was 56.8% (95% confidence interval, 34.1%-71.7%) and was similar across age groups, including adults ≥75 years (aVE, 57.3%; 15.9%-78.4%).

CONCLUSIONS

 During 2010-2011, influenza vaccination was associated with a significant reduction in the risk of laboratory-confirmed influenza hospitalization among adults aged ≥50 years, regardless of age group.

Clinical symptoms cannot predict influenza infection during the 2013 influenza season in Bavaria, Germany

For influenza surveillance and diagnosis typical clinical symptoms are traditionally used to discriminate influenza virus infections from infections by other pathogens. During the 2013 influenza season we performed a multiplex assay for 16 different viruses in 665 swabs from patients with acute respiratory infections (ARIs) to display the variety of different pathogens causing ARI and to test the diagnostic value of both the commonly used case definitions [ARI, and influenza like illness (ILI)] as well as the clinical judgement of physicians, respectively, to achieve a laboratory-confirmed influenza diagnosis. Fourteen different viruses were identified as causing ARI/ILI. Influenza diagnosis based on clinical signs overestimated the number of laboratory-confirmed influenza cases and misclassified cases. Furthermore, ILI case definition and physicians agreed in only 287/651 (44%) cases with laboratory confirmation. Influenza case management has to be supported by laboratory confirmation to allow evidence-based decisions. Epidemiological syndromic surveillance data should be supported by laboratory confirmation for reasonable interpretation.

Application of the screening method to monitor influenza vaccine effectiveness among the elderly in Germany

Background

Elderly people are at increased risk for severe influenza illness and constitute therefore a major target-group for seasonal influenza vaccination in most industrialized countries. The aim of this study was to estimate influenza vaccine effectiveness (VE) among individuals aged 60+ years over three seasons and to assess if the screening method is a suitable tool to monitor influenza VE in this particular target-group in Germany.

Methods

We identified laboratory-confirmed influenza cases aged 60+ years through the national communicable disease reporting system for seasons 2010/11, 2011/12 and 2012/13. Vaccination coverage (VC) data were retrieved from a database of health insurance claims representing ~85% of the total German population. We applied the screening method to calculate influenza subtype-specific VE and compared our results with VE estimates from other observational studies in Europe.

Results

In total, 7,156 laboratory-confirmed influenza cases were included. VE against all influenza types ranged between 49% (95% confidence interval [CI]: 39–56) in 2011/12 and 80% (95% CI: 76-83%) in 2010/11. In 2010/11 subtype-specific VE against influenza A(H1N1)pdm and B was 76% and 84%, respectively. In the following seasons, VE against influenza A(H1N1)pdm, A(H3N2) and B was 87%, -9% , 74% (2011/12), and 74%, 39%, 73% (2012/13). VE was higher among hospitalized compared to non-hospitalized influenza A cases. Seventeen observational studies from Europe reporting subtype-specific VE among the elderly were identified for the respective seasons (all applying the test-negative design) and showed comparable subtype-specific VE estimates.

Conclusions

According to our study, influenza vaccination provided moderate protection against laboratory-confirmed influenza A(H1N1)pdm and B in individuals aged 60+ but no or only little protection against A(H3N2). Higher VE among hospitalized cases might indicate higher protection against severe influenza disease. Based on the available data, the screening method allowed us to assess subtype-specific VE in hospitalized and non-hospitalized elderly persons. Since controlling for several important confounders was not possible, the applied method only provided crude VE estimates. However, given the precise VC-data and the large number of cases, the screening method provided results being in line with VE estimates from other observational studies in Europe that applied a different study design.

Electronic supplementary material

The online version of this article (doi:10.1186/s12879-015-0882-3) contains supplementary material, which is available to authorized users.

Potential of the test-negative design for measuring influenza vaccine effectiveness: a systematic review

BACKGROUND

The test-negative design is a variant of the case-control study being increasingly used to study influenza vaccine effectiveness (VE). In these studies, patients with influenza-like illness are tested for influenza. Vaccine coverage is compared between those testing positive versus those testing negative to estimate VE.

OBJECTIVES

We reviewed features in the design, analysis and reporting of 85 published test-negative studies.

DATA SOURCES

Studies were identified from PubMed, reference lists and email updates. Study eligibility: All studies using the test-negative design reporting end-of-season estimates were included.

STUDY APPRAISAL

Design features that may affect the validity and comparability of reported estimates were reviewed, including setting, study period, source population, case definition, exposure and outcome ascertainment and statistical model.

RESULTS

There was considerable variation in the analytic approach, with 68 unique statistical models identified among the studies.

CONCLUSION

Harmonization of analytic approaches may improve the potential for pooling VE estimates.

Effectiveness of seasonal influenza vaccine in community-dwelling elderly people: a meta-analysis of test-negative design case-control studies

BACKGROUND

The application of test-negative design case-control studies to assess the effectiveness of influenza vaccine has increased substantially in the past few years. The validity of these studies is predicated on the assumption that confounding bias by risk factors is limited by design. We aimed to assess the effectiveness of influenza vaccine in a high-risk group of elderly people.

METHODS

We searched the Cochrane library, Medline, and Embase up to July 13, 2014, for test-negative design case-control studies that assessed the effectiveness of seasonal influenza vaccine against laboratory confirmed influenza in community-dwelling people aged 60 years or older. We used generalised linear mixed models, adapted for test-negative design case-control studies, to estimate vaccine effectiveness according to vaccine match and epidemic conditions.

FINDINGS

35 test-negative design case-control studies with 53 datasets met inclusion criteria. Seasonal influenza vaccine was not significantly effective during local virus activity, irrespective of vaccine match or mismatch to the circulating viruses. Vaccination was significantly effective against laboratory confirmed influenza during sporadic activity (odds ratio [OR] 0·69, 95% CI 0·48-0·99) only when the vaccine matched. Additionally, vaccination was significantly effective during regional (match: OR 0·42, 95% CI 0·30-0·60; mismatch: OR 0·57, 95% CI 0·41-0·79) and widespread (match: 0·54, 0·46-0·62; mismatch: OR 0·72, 95% CI 0·60-0·85) outbreaks.

INTERPRETATION

Our findings show that in elderly people, irrespective of vaccine match, seasonal influenza vaccination is effective against laboratory confirmed influenza during epidemic seasons. Efforts should be renewed worldwide to further increase uptake of the influenza vaccine in the elderly population.

FUNDING

None.

Effectiveness of pandemic and seasonal influenza vaccines in preventing laboratory-confirmed influenza in adults: a clinical cohort study during epidemic seasons 2009-2010 and 2010-2011 in Finland

Background

One dose of pandemic influenza vaccine Pandemrix (GlaxoSmithKline) was offered to the entire population of Finland in 2009–10. We conducted a prospective clinical cohort study to determine the vaccine effectiveness in preventing febrile laboratory-confirmed influenza infection during the influenza season 2009–10 and continued the study in 2010–11.

Methods

In total, 3,518 community dwelling adults aged 18–75 years living in Tampere city were enrolled. The participants were not assigned to any vaccination regimen, but they could participate in the study regardless of their vaccination status or intention to be vaccinated with the pandemic or seasonal influenza vaccine. They were asked to report if they received Pandemrix in 2009–10 and/or trivalent influenza vaccine in 2010–11. Vaccinations were verified from medical records. The participants were instructed to report all acute symptoms of respiratory tract infection with fever (at least 38°C) and pneumonias to the study staff. Nasal and oral swabs were obtained within 5–7 days after symptom onset and influenza-specific RNA was identified by reverse transcription polymerase chain reaction.

Results

In 2009–10, the estimated vaccine effectiveness was 81% (95%CI 30–97). However, the vaccine effectiveness could not be estimated reliably, because only persons in prioritized groups were vaccinated before/during the first pandemic wave and many participants were enrolled when they already had the symptoms of A(H1N1)pdm09 influenza infection. In 2010–11, 2,276 participants continued the follow-up. The vaccine effectiveness, adjusted for potential confounding factors was 81% (95%CI 41–96) for Pandemrix only and 88% (95%CI 63–97) for either Pandemrix or trivalent influenza vaccine 2010–11 or both, respectively.

Conclusion

Vaccination with an AS03-adjuvanted pandemic vaccine in 2009–10 was still effective in preventing A(H1N1)pdm09 influenza during the following epidemic season in 2010–11.

Trial Registration

ClinicalTrials.gov NCT01024725. NCT01206114.

Cost-effectiveness of seasonal influenza vaccination in pregnant women, health care workers and persons with underlying illnesses in Belgium

Risk groups with increased vulnerability for influenza complications such as pregnant women, persons with underlying illnesses as well as persons who come into contact with them, such as health care workers, are currently given priority (along with other classic target groups) to receive seasonal influenza vaccination in Belgium. We aimed to evaluate this policy from a health care payer perspective by cost-effectiveness analysis in the three specific target groups above, while accounting for effects beyond the target group. Increasing the coverage of influenza vaccination is likely to be cost-effective for pregnant women (median €6589 per quality-adjusted life-year (QALY) gained [€4073-€10,249]) and health care workers (median €24,096/QALY gained [€16,442-€36,342]), if this can be achieved without incurring additional administration costs. Assuming an additional physician's consult is charged to administer each additional vaccine dose, the cost-effectiveness of vaccinating pregnant women depends strongly on the extent of its impact on the neonate's health. For health care workers, the assumed number of preventable secondary infections has a strong influence on the cost-effectiveness. Vaccinating people with underlying illnesses is likely highly cost-effective above 50 years of age and borderline cost-effective for younger persons, depending on relative life expectancy and vaccine efficacy in this risk group compared to the general population. The case-fatality ratios of the target group, of the secondary affected groups and vaccine efficacy are key sources of uncertainty.

Positive network assortativity of influenza vaccination at a high school: implications for outbreak risk and herd immunity

Schools are known to play a significant role in the spread of influenza. High vaccination coverage can reduce infectious disease spread within schools and the wider community through vaccine-induced immunity in vaccinated individuals and through the indirect effects afforded by herd immunity. In general, herd immunity is greatest when vaccination coverage is highest, but clusters of unvaccinated individuals can reduce herd immunity. Here, we empirically assess the extent of such clustering by measuring whether vaccinated individuals are randomly distributed or demonstrate positive assortativity across a United States high school contact network. Using computational models based on these empirical measurements, we further assess the impact of assortativity on influenza disease dynamics. We found that the contact network was positively assortative with respect to influenza vaccination: unvaccinated individuals tended to be in contact more often with other unvaccinated individuals than with vaccinated individuals, and these effects were most pronounced when we analyzed contact data collected over multiple days. Of note, unvaccinated males contributed substantially more than unvaccinated females towards the measured positive vaccination assortativity. Influenza simulation models using a positively assortative network resulted in larger average outbreak size, and outbreaks were more likely, compared to an otherwise identical network where vaccinated individuals were not clustered. These findings highlight the importance of understanding and addressing heterogeneities in seasonal influenza vaccine uptake for prevention of large, protracted school-based outbreaks of influenza, in addition to continued efforts to increase overall vaccine coverage.

Effectiveness of the 2010 and 2011 Southern Hemisphere trivalent inactivated influenza vaccines against hospitalization with influenza-associated acute respiratory infection among Thai adults aged ≥ 50 years

Background

Inactivated influenza vaccine (IIV) effectiveness has been evaluated among older adults in high-income countries, but data on IIV effectiveness in low- and middle-income countries remain sparse. We conducted a test-negative case–control analysis to estimate 2010 and 2011 trivalent IIV effectiveness against hospitalization with influenza-associated acute respiratory infection (ARI) among persons aged ≥50 years in rural Thailand.

Methods

During 2010–2011, active surveillance for ARI hospitalization was conducted in two provinces; patients were tested for influenza viruses by real-time RT-PCR. Vaccination status was obtained from vaccine registries. Case and control patients were patients with nasopharyngeal swabs positive and negative for influenza viruses, respectively. Vaccine effectiveness (VE) was estimated for the 6 months after vaccination began. Logistic regression was used to evaluate the association between case status and vaccination while adjusting for age, province, medical conditions, and time.

Results

During 2010–2011, there were 1545 patients with ARI, of whom 279 (18%) were influenza-positive case patients and 1266 (82%) were influenza-negative control patients. Of the 279 case patients, 247 (89%) had influenza A and 32 (11%) had influenza B. Fourteen of 279 (5%) case patients and 108 of 1266 (9%) control patients were vaccinated against influenza. The unadjusted IIV effectiveness against hospitalization with influenza-associated ARI was 43% (95% CI: 0–68%); adjusted VE was 47% (95% CI: 5–71%).

Conclusion

The 2010 and 2011 IIVs were moderately effective against hospitalization with influenza-associated ARI among Thais aged ≥50 years, but IIV coverage was low. Additional efforts are warranted in Thailand to improve IIV uptake in this target group.

Effectiveness of 2012-2013 influenza vaccine against influenza-like illness in general population: estimation in a French web-based cohort

Most of the methods used for estimating the influenza vaccine effectiveness (IVE) target the individuals who have an influenza-like illness (ILI) rather than virologically-proven influenza and access the healthcare system. The objective of this study was to estimate the 2012-2013 IVE in general French population, using a cohort of volunteers registered on GrippeNet.fr, an online surveillance system for ILI. The IVE estimations were obtained through a logistic regression, and analyses were also performed by focusing on at-risk population of severe influenza, and by varying inclusion period and ILI definition. Overall, 1996 individuals were included in the analyses. The corrected IVE was estimated to 49% (20 to 67) for the overall population, and 32% (0 to 58) for the at-risk population. Three covariables appeared with a significant effect on the occurrence of at least one ILI during the epidemic: the age (P = 0.045), the presence of a child in the household (P<10(-3)), and the frequency of cold/flu (P<10(-3)). Comparable results were found at epidemic peak time in the hypothesis of real-time feed of data. In this study, we proposed a novel, follow-up, web-based method to reveal seasonal vaccine effectiveness, which enables analysis in a portion of the population that is not tracked by the health care system in most VE studies.

Field seasonal influenza vaccine effectiveness: evaluation of the screening method using different sources of data during the 2010/2011 French influenza season

Thanks to the screening method, we estimated among target groups the 2010/2011 field vaccine effectiveness (FVE) against laboratory confirmed influenza cases seen in general practice. We also compared the values of FVE estimations obtained by using three sources of the population vaccination coverage (VC) based on three different methodologies: (1) administrative data from the main social security scheme (Caisse Nationale d'Assurance Maladie des Travailleurs Salariés--CNAMTS) covering about 85% of the French population, (2) a cross-sectional national telephone survey in the general population, and (3) a declarative survey in the population seen in a one-day general practitioner (GP) consultations. The FVE estimates among target groups were stratified by age (< 65 y old with reported chronic illness; ≥65 y old and overall). Using the VC of the CNAMTS, the FVE of the 2010/2011 seasonal trivalent vaccine against laboratory confirmed infection with any influenza virus was 59% (95% Confidence Interval, 17 to 81). It was 85% (17 to 99) and 50% (-16 to 80) for A(H1N1)pdm09 and B influenza infections, respectively. The values of FVE using the influenza VC obtained in a sample of the general population and of the population of GPs' patients were 73% (45 to 87) and 82% (63 to 92), respectively. We estimated a moderate influenza FVE in preventing confirmed influenza viruses in target groups by using the VC of the CNAMTS. We also observed that the screening method generates FVE values dependent on the choice of the source of VC and thus should be used cautiously.