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PLoS Medicine - The Effect of Universal Influenza Immunization on Mortality and Health Care Use
The Effect of Universal Influenza Immunization on Mortality and Health Care Use
Jeffrey C. Kwong1,2,3*, Th?r?se A. Stukel1,4, Jenny Lim1, Allison J. McGeer5,6, Ross E. G. Upshur1,2,3,7, Helen Johansen8, Christie Sambell9, William W. Thompson10, Deva Thiruchelvam1, Fawziah Marra11, Lawrence W. Svenson12,13,14, Douglas G. Manuel1,2
1 Institute for Clinical Evaluative Sciences, Toronto, Ontario, Canada,
2 Dalla Lana School of Public Health, University of Toronto, Toronto, Ontario, Canada,
3 Department of Family and Community Medicine, University of Toronto, Toronto, Ontario, Canada,
4 Department of Health Policy, Management and Evaluation, University of Toronto, Toronto, Ontario, Canada,
5 Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, Ontario, Canada,
6 Mount Sinai Hospital, Department of Microbiology, Toronto, Ontario, Canada,
7 Sunnybrook Health Sciences Centre Primary Care Research Unit, Toronto, Ontario, Canada,
8 Health Information and Research Division, Statistics Canada, Ottawa, Ontario, Canada,
9 Health Statistics Division, Statistics Canada, Ottawa, Ontario, Canada,
10 Influenza Division, National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia, United States of America,
11 British Columbia Centre for Disease Control, Vancouver, British Columbia, Canada,
12 Alberta Health and Wellness, Edmonton, Alberta, Canada,
13 Department of Public Health Sciences, University of Alberta, Edmonton, Alberta, Canada,
14 Department of Community Health Sciences, University of Calgary, Calgary, Alberta, Canada
Background
In 2000, Ontario, Canada, initiated a universal influenza immunization program (UIIP) to provide free influenza vaccines for the entire population aged 6 mo or older. Influenza immunization increased more rapidly in younger age groups in Ontario compared to other Canadian provinces, which all maintained targeted immunization programs. We evaluated the effect of Ontario's UIIP on influenza-associated mortality, hospitalizations, emergency department (ED) use, and visits to doctors' offices.
Methods and Findings
Mortality and hospitalization data from 1997 to 2004 for all ten Canadian provinces were obtained from national datasets. Physician billing claims for visits to EDs and doctors' offices were obtained from provincial administrative datasets for four provinces with comprehensive data. Since outcomes coded as influenza are known to underestimate the true burden of influenza, we studied more broadly defined conditions. Hospitalizations, ED use, doctors' office visits for pneumonia and influenza, and all-cause mortality from 1997 to 2004 were modelled using Poisson regression, controlling for age, sex, province, influenza surveillance data, and temporal trends, and used to estimate the expected baseline outcome rates in the absence of influenza activity. The primary outcome was then defined as influenza-associated events, or the difference between the observed events and the expected baseline events. Changes in influenza-associated outcome rates before and after UIIP introduction in Ontario were compared to the corresponding changes in other provinces. After UIIP introduction, influenza-associated mortality decreased more in Ontario (relative rate [RR] = 0.26) than in other provinces (RR = 0.43) (ratio of RRs = 0.61, p = 0.002). Similar differences between Ontario and other provinces were observed for influenza-associated hospitalizations (RR = 0.25 versus 0.44, ratio of RRs = 0.58, p < 0.001), ED use (RR = 0.31 versus 0.69, ratio of RRs = 0.45, p < 0.001), and doctors' office visits (RR = 0.21 versus 0.52, ratio of RRs = 0.41, p < 0.001). Sensitivity analyses were carried out to assess consistency, specificity, and the presence of a dose-response relationship. Limitations of this study include the ecological study design, the nonspecific outcomes, difficulty in modeling baseline events, data quality and availability, and the inability to control for potentially important confounders.
Conclusions
Compared to targeted programs in other provinces, introduction of universal vaccination in Ontario in 2000 was associated with relative reductions in influenza-associated mortality and health care use. The results of this large-scale natural experiment suggest that universal vaccination may be an effective public health measure for reducing the annual burden of influenza.
Funding:
This study was supported by an operating grant from the Public Health Agency of Canada, a Fellowship Award (to JCK), a Canada Research Chair Award in Primary Care Research (to REGU), and a Chair in Applied Public Health (to DGM) from the Canadian Institutes of Health Research, and a Career Scientist Award from the Ontario Ministry of Health and Long-Term Care (to DGM). The Institute for Clinical Evaluative Sciences (ICES) is supported in part by a grant from the Ontario Ministry of Health and Long-Term Care. Funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. The findings and conclusions in this study are those of the authors and do not necessarily represent the views of the Centers for Disease Control and Prevention, the Institute for Clinical Evaluative Sciences, the Ontario Ministry of Health and Long-Term Care, or Manitoba Health and Healthy Living.
Competing Interests:
AJM reports receiving travel grants from Sanofi Pasteur and Solvay Pharmaceuticals for speaking at meetings, and payment from Sanofi Pasteur for chairing a safety committee for a clinical trial.
Academic Editor:
Joseph Peiris, The University of Hong Kong, Hong Kong
Citation: Kwong JC, Stukel TA, Lim J, McGeer AJ, Upshur REG, et al. (2008) The Effect of Universal Influenza Immunization on Mortality and Health Care Use. PLoS Med 5(10): e211 doi:10.1371/journal.pmed.0050211
Received: February 6, 2008; Accepted: September 10, 2008; Published: October 28, 2008
This is an open-access article distributed under the terms of the Creative Commons Public Domain declaration, which stipulates that, once placed in the public domain, this work may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose.
Abbreviations:
CI, confidence interval; ED, emergency department; P&I, pneumonia and influenza; R&C, respiratory and circulatory; RR, relative rate; UIIP, universal influenza immunization program
* To whom correspondence should be addressed. E-mail: jeff.kwong@utoronto.ca
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<cite cite="http://medicine.plosjournals.org/perlserv/?request=get-document&doi=10.1371/journal.pmed.0050211">PLoS Medicine - The Effect of Universal Influenza Immunization on Mortality and Health Care Use</cite>
Jeffrey C. Kwong1,2,3*, Th?r?se A. Stukel1,4, Jenny Lim1, Allison J. McGeer5,6, Ross E. G. Upshur1,2,3,7, Helen Johansen8, Christie Sambell9, William W. Thompson10, Deva Thiruchelvam1, Fawziah Marra11, Lawrence W. Svenson12,13,14, Douglas G. Manuel1,2
1 Institute for Clinical Evaluative Sciences, Toronto, Ontario, Canada,
2 Dalla Lana School of Public Health, University of Toronto, Toronto, Ontario, Canada,
3 Department of Family and Community Medicine, University of Toronto, Toronto, Ontario, Canada,
4 Department of Health Policy, Management and Evaluation, University of Toronto, Toronto, Ontario, Canada,
5 Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, Ontario, Canada,
6 Mount Sinai Hospital, Department of Microbiology, Toronto, Ontario, Canada,
7 Sunnybrook Health Sciences Centre Primary Care Research Unit, Toronto, Ontario, Canada,
8 Health Information and Research Division, Statistics Canada, Ottawa, Ontario, Canada,
9 Health Statistics Division, Statistics Canada, Ottawa, Ontario, Canada,
10 Influenza Division, National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia, United States of America,
11 British Columbia Centre for Disease Control, Vancouver, British Columbia, Canada,
12 Alberta Health and Wellness, Edmonton, Alberta, Canada,
13 Department of Public Health Sciences, University of Alberta, Edmonton, Alberta, Canada,
14 Department of Community Health Sciences, University of Calgary, Calgary, Alberta, Canada
Background
In 2000, Ontario, Canada, initiated a universal influenza immunization program (UIIP) to provide free influenza vaccines for the entire population aged 6 mo or older. Influenza immunization increased more rapidly in younger age groups in Ontario compared to other Canadian provinces, which all maintained targeted immunization programs. We evaluated the effect of Ontario's UIIP on influenza-associated mortality, hospitalizations, emergency department (ED) use, and visits to doctors' offices.
Methods and Findings
Mortality and hospitalization data from 1997 to 2004 for all ten Canadian provinces were obtained from national datasets. Physician billing claims for visits to EDs and doctors' offices were obtained from provincial administrative datasets for four provinces with comprehensive data. Since outcomes coded as influenza are known to underestimate the true burden of influenza, we studied more broadly defined conditions. Hospitalizations, ED use, doctors' office visits for pneumonia and influenza, and all-cause mortality from 1997 to 2004 were modelled using Poisson regression, controlling for age, sex, province, influenza surveillance data, and temporal trends, and used to estimate the expected baseline outcome rates in the absence of influenza activity. The primary outcome was then defined as influenza-associated events, or the difference between the observed events and the expected baseline events. Changes in influenza-associated outcome rates before and after UIIP introduction in Ontario were compared to the corresponding changes in other provinces. After UIIP introduction, influenza-associated mortality decreased more in Ontario (relative rate [RR] = 0.26) than in other provinces (RR = 0.43) (ratio of RRs = 0.61, p = 0.002). Similar differences between Ontario and other provinces were observed for influenza-associated hospitalizations (RR = 0.25 versus 0.44, ratio of RRs = 0.58, p < 0.001), ED use (RR = 0.31 versus 0.69, ratio of RRs = 0.45, p < 0.001), and doctors' office visits (RR = 0.21 versus 0.52, ratio of RRs = 0.41, p < 0.001). Sensitivity analyses were carried out to assess consistency, specificity, and the presence of a dose-response relationship. Limitations of this study include the ecological study design, the nonspecific outcomes, difficulty in modeling baseline events, data quality and availability, and the inability to control for potentially important confounders.
Conclusions
Compared to targeted programs in other provinces, introduction of universal vaccination in Ontario in 2000 was associated with relative reductions in influenza-associated mortality and health care use. The results of this large-scale natural experiment suggest that universal vaccination may be an effective public health measure for reducing the annual burden of influenza.
Funding:
This study was supported by an operating grant from the Public Health Agency of Canada, a Fellowship Award (to JCK), a Canada Research Chair Award in Primary Care Research (to REGU), and a Chair in Applied Public Health (to DGM) from the Canadian Institutes of Health Research, and a Career Scientist Award from the Ontario Ministry of Health and Long-Term Care (to DGM). The Institute for Clinical Evaluative Sciences (ICES) is supported in part by a grant from the Ontario Ministry of Health and Long-Term Care. Funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. The findings and conclusions in this study are those of the authors and do not necessarily represent the views of the Centers for Disease Control and Prevention, the Institute for Clinical Evaluative Sciences, the Ontario Ministry of Health and Long-Term Care, or Manitoba Health and Healthy Living.
Competing Interests:
AJM reports receiving travel grants from Sanofi Pasteur and Solvay Pharmaceuticals for speaking at meetings, and payment from Sanofi Pasteur for chairing a safety committee for a clinical trial.
Academic Editor:
Joseph Peiris, The University of Hong Kong, Hong Kong
Citation: Kwong JC, Stukel TA, Lim J, McGeer AJ, Upshur REG, et al. (2008) The Effect of Universal Influenza Immunization on Mortality and Health Care Use. PLoS Med 5(10): e211 doi:10.1371/journal.pmed.0050211
Received: February 6, 2008; Accepted: September 10, 2008; Published: October 28, 2008
This is an open-access article distributed under the terms of the Creative Commons Public Domain declaration, which stipulates that, once placed in the public domain, this work may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose.
Abbreviations:
CI, confidence interval; ED, emergency department; P&I, pneumonia and influenza; R&C, respiratory and circulatory; RR, relative rate; UIIP, universal influenza immunization program
* To whom correspondence should be addressed. E-mail: jeff.kwong@utoronto.ca
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