As flu season approaches, researchers offer one more reason for Canadians to get the flu vaccine. New research suggests more vaccinations would lead to fewer flu-related doctor's office visits, hospitalizations and deaths.

In a study published in the open-access journal PLoS Medicine, researchers found that the number of flu-related deaths in the province dropped 40 per cent after Ontario introduced its universal flu shot program eight years ago.

As well, flu-related visits to emergency rooms, doctors and hospitals dropped between 40 and 60 per cent.

"By vaccinating as many people as possible, we can reduce the number of people getting ill and passing on the infection to others," Dr. Jeffrey Kwong, of the Dalla Lana School of Public Health at the University of Toronto and one of the study's authors, told Â鶹´«Ã½.

Kwong said the findings show that on average each year, Ontario's flu shot program prevents:

  • 300 deaths
  • 1,000 hospitalizations
  • 30,000 emergency room visits
  • 200,000 visits to the doctor

Kwong called the phenomenon "herd immunity," meaning that vaccinating more people will reduce flu transmission rates.

In 2000, Ontario introduced its universal flu vaccination program, which provides free vaccines for anyone aged six months or older.

As a result, immunization rates among younger age groups increased rapidly compared to younger populations of other provinces.

About 40 per cent of senior citizens in Ontario now get the flu shot, while 25 per cent of adults aged 25 to 49 get vaccinated, Kwong said.

While those rates seem low, they are still higher than other provinces, Kwong said. Other provinces have targeted vaccination programs aimed at at-risk populations such as the elderly, children and those with compromised immune systems.

The findings may encourage other provinces and countries to consider universal vaccination programs, Kwong said.

Dr. Allison McGeer of Mount Sinai Hospital, another of the study's authors, said this year may be a good year for more people to get the flu vaccine.

Each year, the World Health Organization formulates the vaccine with three flu strains its experts feel will be most prominent during flu season.

Because this year's vaccine has three new strains, experts have speculated that health officials fear a bad flu season.

"Because all the strains are new, it's a really good year to get the flu vaccine because you won't have had much exposure (to the strains) and you are more likely to get sick," McGeer told Â鶹´«Ã½.

With a report from CTV's medical specialist Avis Favaro and senior producer Elizabeth St. Philip

Abstract:

The Effect of Universal Influenza Immunization on Mortality and Health Care Use

Jeffrey C. Kwong, Therese A. Stukel, Jenny Lim, Allison J. McGeer, Ross E.G. Upshur, Helen Johansen, Christie Sambell, William W. Thompson, Deva Thiruchelvam, Fawziah Marra, Lawrence W. Svenson, Douglas G. Manuel

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 non-specific 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.