Effectiveness of Seasonal Influenza Vaccines in the United States During a Season With Circulation of All Three Vaccine Strains

Department of Medicine, University of Rochester Medical Center, New York.
Clinical Infectious Diseases (Impact Factor: 8.89). 07/2012; 55(7):951-959. DOI: 10.1093/cid/cis574
Source: PubMed


Influenza vaccines may be reformulated annually because of antigenic drift in influenza viruses. However, the relationship between antigenic characteristics of circulating viruses and vaccine effectiveness (VE) is not well understood. We conducted an assessment of the effectiveness of US influenza vaccines during the 2010-2011 season.

We performed a case-control study comparing vaccination histories between subjects with acute respiratory illness with positive real-time reverse transcription polymerase chain reaction for influenza and influenza test-negative controls. Subjects with acute respiratory illness of ≤7 days duration were enrolled in hospitals, emergency departments, or outpatient clinics in communities in 4 states. History of immunization with the 2010-2011 vaccine was ascertained from vaccine registries or medical records. Vaccine effectiveness was estimated in logistic regression models adjusted for study community, age, race, insurance status, enrollment site, and presence of a high-risk medical condition.

A total of 1040 influenza-positive cases and 3717 influenza-negative controls were included from the influenza season, including 373 cases of influenza A(H1N1), 334 cases of influenza A(H3N2), and 333 cases of influenza B. Overall adjusted VE was 60% (95% confidence interval [CI], 53%-66%). Age-specific VE estimates ranged from 69% (95% CI, 56%-77%) in children aged 6 months-8 years to 38% (95% CI, -16% to 67%) in adults aged ≥65 years.

The US 2010-2011 influenza vaccines were moderately effective in preventing medically attended influenza during a season when all 3 vaccine strains were antigenically similar to circulating viruses. Continued monitoring of influenza vaccines in all age groups is important, particularly as new vaccines are introduced.

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    • "We used estimates that from subjects of a broad age range (e.g. 6 months or older or 18–48 yrs.) or were restricted to one of our age groups (e.g. ≥65 yrs.) [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] (Table 1). Up to 2010/11 we mostly used the same estimates Kostova et al. [6] for their analysis of cases and hospitalizations averted by influenza vaccination; however, we excluded one unpublished study (see reference 11 in [6]) and one study that included non-North American populations [23], added one study that had been published since [16] as well as three studies estimating VE for the three recent influenza seasons (2011/12, 2012/13 and 2013/14, respectively) [20] [24] [25]. "
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    ABSTRACT: Excess mortality due to seasonal influenza is substantial, yet quantitative estimates of the benefit of annual vaccination programs on influenza-associated mortality are lacking. We estimated the numbers of deaths averted by vaccination in four age groups (0.5 to 4, 5 to 19, 20 to 64 and ≥65 yrs.) for the nine influenza seasons from 2005/6 through 2013/14. These estimates were obtained using a Monte Carlo approach applied to weekly U.S. age group-specific estimates of influenza-associated excess mortality, monthly vaccination coverage estimates and summary seasonal influenza vaccine effectiveness estimates to obtain estimates of the number of deaths averted by vaccination. The estimates are conservative as they do not include indirect vaccination effects. From August, 2005 through June, 2014, we estimated that 40,127 (95% confidence interval [CI] 25,694 to 59,210) deaths were averted by influenza vaccination. We found that of all studied seasons the most deaths were averted by influenza vaccination during the 2012/13 season (9398; 95% CI 2,386 to 19,897) and the fewest during the 2009/10 pandemic (222; 95% CI 79 to 347). Of all influenza-associated deaths averted, 88.9% (95% CI 83 to 92.5%) were in people ≥65 yrs. old. The estimated number of deaths averted by the US annual influenza vaccination program is considerable, especially among elderly adults and even when vaccine effectiveness is modest, such as in the 2012/13 season. As indirect effects ("herd immunity") of vaccination are ignored, these estimates represent lower bound estimates and are thus conservative given valid excess mortality estimates. Copyright © 2015 The Authors. Published by Elsevier Ltd.. All rights reserved.
    Vaccine 03/2015; 99(26). DOI:10.1016/j.vaccine.2015.02.042 · 3.62 Impact Factor
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    • "Current inactivated trivalent influenza vaccine (TIV) strategies rely on the induction of an antibody-mediated immune response specific for the antigenically varying hemagglutinin (HA) surface antigen. TIV have only moderate efficacy or effectiveness [4] [5] and is particularly impeded when the circulating strain has drifted significantly from the vaccine strain. A recent meta-analysis of TIV studies found that anti-HA antibodies are only partial correlates of protection in the general population and poor correlates of protection in the elderly [4]. "
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    ABSTRACT: Background FP-01.1 is a novel synthetic influenza A vaccine consisting of six fluorocarbon-modified 35-mer peptides that encapsulate multiple CD4+ and CD8+ T-cell epitopes and is designed to induce an immune response across a broad population. Methods FP-01.1 was evaluated for safety and immunogenicity in a randomised, double-blind, placebo-controlled, dose-escalation, phase I clinical study in healthy adult volunteers (n = 49). IFNγ ELISpot assays and multicolour flow cytometry were used to characterise the immune response. Results FP-01.1 was safe and well tolerated at all doses tested with a similar adverse event profile in actively vaccinated subjects compared with controls. Maximum immunogenicity was in the 150 μg/peptide dose group where a robust response (243 spots/million PBMC) was demonstrated in 75% subjects compared with 0% in placebo controls. All six peptides were immunogenic. FP-01.1 induced dual CD4+ and CD8+ T cell responses and vaccine-specific T cells cross-recognise divergent influenza strains. Conclusions This first-in-human study showed that FP-01.1 has an acceptable safety and tolerability profile and generated robust anti-viral T cell responses in a high proportion of subjects tested. The results support the further clinical testing of FP-01.1 prior to clinical, proof-of-concept, live viral challenge studies.
    Vaccine 12/2014; 33(2). DOI:10.1016/j.vaccine.2014.06.006 · 3.62 Impact Factor
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    • "Analyses were performed separately for vaccine effectiveness, vaccine efficacy and their upper and lower 95% confidence intervals (CI), and by age group and presence of underlying conditions. Overall vaccine effectiveness estimates were obtained from a single US study performed during the 2010/11 influenza season where co-circulation of influenza A (H1N1), A(H3N2) and B was observed [4]. Estimates ranged from 56% (95% CI: 31 to 74) among children 6 months-2 years of age to 36% (95% CI: 22 to 66) among subjects ≥65 years. "
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    ABSTRACT: Seasonal influenza vaccination coverage in most EU/EEA remains suboptimal. Providers' and users' confidence in influenza vaccines is undermined by reports of moderate to low vaccine effectiveness and by the lack of solid evidence on disease burden. A study from Preaud and co. indicates that even with current levels of vaccine effectiveness, increasing vaccination coverage would significantly reduce disease burden and health cost. The results of the study should be interpreted cautiously because some of the assumptions are not generalizable or are imprecise, especially those on vaccine coverage, disease burden and health cost. Increasing vaccination coverage in EU/EEA countries is very challenging. Multifaceted approaches and country specific strategies are needed to address vaccine hesitancy in health care workers and in the population, and to manage organisational and financial obstacles. One key element for increasing vaccination coverage is the development of better influenza vaccines, e.g. vaccines that are more effective, provide longer lasting immunity and do not require annual administration. Vaccine producers should consider this as the highest research priority in the field of influenza vaccine development.
    BMC Public Health 08/2014; 14(1):818. DOI:10.1186/1471-2458-14-818 · 2.26 Impact Factor
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