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. 2021 Sep 7;73(5):e1191-e1199.
doi: 10.1093/cid/ciaa1862.

Influenza Vaccine Effectiveness Against All-Cause Mortality Following Laboratory-Confirmed Influenza in Older Adults, 2010-2011 to 2015-2016 Seasons in Ontario, Canada

Hannah Chung  1 , Sarah A Buchan  1   2   3 , Aaron Campigotto  4   5   6 , Michael A Campitelli  1 , Natasha S Crowcroft  1   3   7   6 , Vinita Dubey  3   8 , Jonathan B Gubbay  2   4   6 , Timothy Karnauchow  9   10 , Kevin Katz  11 , Allison J McGeer  3   6   12 , J Dayre McNally  9 , Samira Mubareka  13 , Michelle Murti  2   3 , David C Richardson  14 , Laura C Rosella  1   2   3 , Kevin L Schwartz  1   2   3 , Marek Smieja  15 , George Zahariadis  5   16 , Jeffrey C Kwong  1   2   3   7   17   18
Affiliations

Influenza Vaccine Effectiveness Against All-Cause Mortality Following Laboratory-Confirmed Influenza in Older Adults, 2010-2011 to 2015-2016 Seasons in Ontario, Canada

Hannah Chung et al. Clin Infect Dis. .

Abstract

Background: Older adults are at increased risk of mortality from influenza infections. We estimated influenza vaccine effectiveness (VE) against mortality following laboratory-confirmed influenza.

Methods: Using a test-negative design study and linked laboratory and health administrative databases in Ontario, Canada, we estimated VE against all-cause mortality following laboratory-confirmed influenza for community-dwelling adults aged >65 years during the 2010-2011 to 2015-2016 influenza seasons.

Results: Among 54 116 older adults tested for influenza across the 6 seasons, 6837 died within 30 days of specimen collection. Thirteen percent (925 individuals) tested positive for influenza, and 50.6% were considered vaccinated for that season. Only 23.2% of influenza test-positive cases had influenza recorded as their underlying cause of death. Before and after multivariable adjustment, we estimated VE against all-cause mortality following laboratory-confirmed influenza to be 20% (95% confidence interval [CI], 8%-30%) and 20% (95% CI, 7%-30%), respectively. This estimate increased to 34% after correcting for influenza vaccination exposure misclassification. We observed significant VE against deaths following influenza confirmation during 2014-2015 (VE = 26% [95% CI, 5%-42%]). We also observed significant VE against deaths following confirmation of influenza A/H1N1 and A/H3N2, and against deaths with COPD as the underlying cause.

Conclusions: These results support the importance of influenza vaccination in older adults, who account for most influenza-associated deaths annually.

Keywords: influenza vaccine; mortality; older adults; vaccine effectiveness.

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Figures

Figure 1.
Figure 1.
Proportion with underlying causes of death for varying intervals from specimen collection to death among community-dwelling older adults during the 2010–2011 to 2015–2016 influenza seasons in Ontario, Canada. Sum of the proportions for each interval per exposure group does not equal 100%. Of the 10 150 individuals who died within 90 days of specimen collection, 2698 individuals had an underlying cause of death that was not included in one of the selected categories, and 51 individuals do not have an underlying cause of death, because either their death was not registered in the Office of the Registrar General–Death database or their underlying cause of death was not determined. Abbreviation: COPD, chronic obstructive pulmonary disease.
Figure 2.
Figure 2.
Influenza vaccine effectiveness for community-dwelling adults aged >65 years against all-cause mortality following laboratory-confirmed influenza for cumulative intervals (a) and mutually exclusive intervals (b) from specimen collection to death for any influenza and by type/subtype. Abbreviation: VE, vaccine effectiveness.
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