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Observational Study
. 2017 Aug 15;216(4):405-414.
doi: 10.1093/infdis/jix282.

The Importance of Frailty in the Assessment of Influenza Vaccine Effectiveness Against Influenza-Related Hospitalization in Elderly People

Melissa K Andrew  1 , Vivek Shinde  2 , Lingyun Ye  1 , Todd Hatchette  1 , François Haguinet  2 , Gael Dos Santos  3 , Janet E McElhaney  4 , Ardith Ambrose  1 , Guy Boivin  5 , William Bowie  6 , Ayman Chit  7   8 , May ElSherif  1 , Karen Green  9 , Scott Halperin  1 , Barbara Ibarguchi  10 , Jennie Johnstone  11 , Kevin Katz  12 , Joanne Langley  1 , Jason Leblanc  1 , Mark Loeb  11 , Donna MacKinnon-Cameron  1 , Anne McCarthy  13 , Allison McGeer  9 , Jeff Powis  14 , David Richardson  15 , Makeda Semret  16 , Grant Stiver  6 , Sylvie Trottier  5 , Louis Valiquette  17 , Duncan Webster  18 , Shelly A McNeil  1 ; Serious Outcomes Surveillance Network of the Public Health Agency of Canada/Canadian Institutes of Health Research Influenza Research Network (PCIRN) and the Toronto Invasive Bacterial Diseases Network (TIBDN)
Affiliations
Observational Study

The Importance of Frailty in the Assessment of Influenza Vaccine Effectiveness Against Influenza-Related Hospitalization in Elderly People

Melissa K Andrew et al. J Infect Dis. .

Abstract

Background: Influenza is an important cause of morbidity and mortality among older adults. Even so, effectiveness of influenza vaccine for older adults has been reported to be lower than for younger adults, and the impact of frailty on vaccine effectiveness (VE) and outcomes is uncertain. We aimed to study VE against influenza hospitalization in older adults, focusing on the impact of frailty.

Methods: We report VE of trivalent influenza vaccine (TIV) in people ≥65 years of age hospitalized during the 2011-2012 influenza season using a multicenter, prospective, test-negative case-control design. A validated frailty index (FI) was used to measure frailty.

Results: Three hundred twenty cases and 564 controls (mean age, 80.6 and 78.7 years, respectively) were enrolled. Cases had higher baseline frailty than controls (P = .006). In the fully adjusted model, VE against influenza hospitalization was 58.0% (95% confidence interval [CI], 34.2%-73.2%). The contribution of frailty was important; adjusting for frailty alone yielded a VE estimate of 58.7% (95% CI, 36.2%-73.2%). VE was 77.6% among nonfrail older adults and declined as frailty increased.

Conclusions: Despite commonly held views that VE is poor in older adults, we found that TIV provided good protection against influenza hospitalization in older adults who were not frail, though VE diminished as frailty increased.

Clinical trials registration: NCT01517191.

Keywords: elderly; frailty; hospitalization; influenza; vaccine effectiveness.

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Figures

Figure 1.
Figure 1.
Patient disposition. Abbreviations: N, number of subjects in group; n, number of subjects fulfilling case definition; VE, vaccine effectiveness.
Figure 2.
Figure 2.
Laboratory-confirmed influenza cases and test-negative controls by week and virus subtype, 1 November 2011 to 25 May 2012. Includes all laboratory-confirmed cases enrolled by the Serious Outcomes Surveillance Network of the Public Health Agency of Canada/Canadian Institutes of Health Research Influenza Research Network over the study period. Of the 588 cases enrolled, 528 cases were included in the vaccine effectiveness analysis.
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