Influenza vaccine effectiveness among adult patients in a University of Lyon hospital (2004–2009)

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.

Influenza vaccine effectiveness among healthcare workers in comparison to hospitalized patients: A 2004-2009 case-test, negative-control, prospective study

The objective of this study was to calculate Vaccine Effectiveness (VE) in healthcare workers (HCW) and to compare VE between patients and HCW. A case-control investigation based on the prospective study was conducted between 2004 and 2009 in a teaching hospital. All HCW with influenza-like illness (ILI) from participating units (n = 24) were included, and vaccination status was characterized by interview. A total of 150 HCW presented ILI; 130 (87%) were female, 27 (18%) were positive for influenza, and 42 (28%) were vaccinated. Adjusted VE was 89% (95% CI 39 to 98). Among patients, adjusted VE was 42% (95% CI -39 to 76). The difference of VE (VEhcw - VEpat) was 46.15% (95% CI 2.41 to 144). The VE ratio (VEhcw / VEpat) was 2.09 (95% CI -1.60 to 134.17). Influenza VE differed between HCW and patients when the flu season was taken into account. This finding confirms the major impact of host determinants on influenza VE.

Evaluating the case-positive, control test-negative study design for influenza vaccine effectiveness for the frailty bias

INTRODUCTION

Previous influenza vaccine effectiveness studies were criticized for their failure to control for frailty. This study was designed to see if the test-negative study design overcomes this bias.

METHODS

Adults ≥ 50 years of age with respiratory symptoms were enrolled from November 2006 through May 2012 during the influenza season (excluding the 2009-2010 H1N1 pandemic season) to perform yearly test-negative control influenza vaccine effectiveness studies in Nashville, TN. At enrollment, both a nasal and throat swab sample were obtained and tested for influenza by RT-PCR. Frailty was calculated using a modified Rockwood Index that included 60 variables ascertained in a retrospective chart review giving a score of 0 to 1. Subjects were divided into three strata: non frail (≤ 0.08), pre-frail (> 0.08 to < 0.25), and frail (≥ 0.25). Vaccine effectiveness was calculated using the formula [1-adjusted odds ratio (OR)] × 100%. Adjusted ORs for individual years and all years combined were estimated by penalized multivariable logistic regression.

RESULTS

Of 1023 hospitalized adults enrolled, 866 (84.7%) participants had complete immunization status, molecular influenza testing and covariates to calculate frailty. There were 83 influenza-positive cases and 783 test-negative controls overall, who were 74% white, 25% black, and 59% female. The median frailty index was 0.167 (Interquartile: 0.117, 0.267). The frailty index was 0.167 (0.100, 0.233) for the influenza positive cases compared to 0.183 (0.133, 0.267) for influenza negative controls (p = 0.07). Vaccine effectiveness estimates were 55.2% (95%CI: 30.5, 74.2), 60.4% (95%CI: 29.5, 74.4), and 54.3% (95%CI: 28.8, 74.0) without the frailty variable, including frailty as a continuous variable, and including frailty as a categorical variable, respectively.

CONCLUSIONS

Using the case positive test negative study design to assess vaccine effectiveness, our measure of frailty was not a significant confounder as inclusion of this measure did not significantly change vaccine effectiveness estimates.

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.

Influenza vaccine prevents medically attended influenza-associated acute respiratory illness in adults aged ≥50 years

BACKGROUND

There are few estimates of effectiveness influenza vaccine in preventing serious outcomes due to influenza in older adults.

METHODS

Adults aged ≥50 years who sought medical care for acute respiratory illness were enrolled. A nose/throat swab was tested for influenza virus by reverse transcription-polymerase chain reaction. Clinical and demographic data were collected, including verification of receipt of trivalent inactivated influenza vaccination (IIV-3). Adjusted odds ratios were estimated by multivariable logistic regression models with an L1 penalty on all covariates except vaccination status.

RESULTS

A total of 1047 subjects were enrolled from November through April during 5 influenza seasons during 2006-2012, excluding the 2009-2010 season. Of those enrolled, 927 (88%) had complete influenza virus testing, vaccination status, and demographic data obtained. Of 86 (9.3%) influenza virus-positive patients, 47 (55%) were vaccinated. Of 841 influenza virus-negative patients, 646 (76.8%) were vaccinated. Over 5 influenza seasons, IIV-3 was 58.4% effective (95% confidence interval [CI], 37.0%-75.6%) for the prevention of medically attended laboratory-confirmed influenza illness in adults aged ≥50 years and 58.4% effective (95% CI, 7.9%-81.1%) in adults aged ≥65 years.

CONCLUSIONS

Influenza vaccine was moderately effective in preventing influenza-associated medical care visits in older adults.

Rabbit nasal immunization against influenza by dry-powder form of chitosan nanospheres encapsulated with influenza whole virus and adjuvants

Influenza virus is one of the main causes of respiratory diseases in human. Although different vaccines have been produced during past decades, there is still a huge demand for a safe influenza vaccine with the ability to induce mucosal immune responses and sufficient protection, especially in elderly patients. In this study, chitosan nanospheres were employed as the drug delivery system. Influenza virus, CpG oligodeoxynucleotide (CpG ODN) and Quillaja saponins (QS) were incorporated in this nanospheric system. Three doses of dry powder nanosphere vaccine were nasally administered to rabbits on days 0, 45 and 60, followed by a final booster injection on day 75. Both humoral and cellular immune responses were investigated. Hemagglutination inhibition (HI) antibody titer was elevated in all groups compared to the control group at the end of vaccination in rabbits receiving nanospheres loaded with virus and CpG, CH(WV+CpG) (P<0.001). Rabbit serum IgG raised significantly in all the vaccinated groups, with the highest responses in CH(WV+CpG) group. CH(WV+CpG) and CH(WV) induced significant sIgA titers (P<0.001). CpG adjuvant also showed a prominent role in the stimulation and secretion of of IL-2 and IFN-γ cytokines (3 and 3.5 fold increase, respectively). Finally, as CH(WV+CpG) depicted to be effective in induction of humoral and cellular immune responses after nasal administration, this nanoparticulate adjuvant could be identified as an efficient adjuvant/delivery system for mucosal immunization against influenza virus.

Protective efficacy of a bacterially produced modular capsomere presenting M2e from influenza: extending the potential of broadly cross-protecting epitopes

Influenza A viruses drift and shift, emerging as antigenically distinct strains that lead to epidemics and pandemics of varying severity. Even epitopes associated with broad cross-protection against different strains, such as the ectodomain of matrix protein 2 (M2e), mutate unpredictably. Vaccine protective efficacy is only ensured when the emerging virus lies within the vaccine's cross-protective domain, which is poorly defined in most situations. When virus emerges outside this domain it is essential to rapidly re-engineer the vaccine and hence re-center the cross-protective domain on the new virus. This approach of vaccine re-engineering in response to virus change is the cornerstone of the current influenza control system, based on annual prediction and/or pandemic reaction. This system could become more responsive, and perhaps preventative, if its speed could be improved. Here, we demonstrate vaccine efficacy of a rapidly manufacturable modular capsomere presenting the broadly cross-protecting M2e epitope from influenza. M2e inserted into a viral capsomere at the DNA level was expressed in Escherichia coli as a fusion protein (Wibowo et al., 2013). Immunization of mice with this modular capsomere adjuvanted with conventional aluminum hydroxide induced high (more than 10(5) endpoint titer) levels of M2e-specific antibodies that reduced disease severity and viral load in the lungs of challenged mice. The combination of rapid manufacturability of modular capsomere presented in this study, and the established cross-protective efficacy of M2e, allow rapid matching of vaccine to the circulating virus and hence rapid re-centering of the vaccine's cross-protective domain onto the virus. This approach synergizes the discussed benefits of broadly cross-protecting epitopes with rapid scale-up vaccine manufacture using microbial cell factories.