The Canadian province of Ontario initiated a universal immunization program in 2000, in which flu vaccination is promoted and provided free of charge to everyone over the age of 6 months.

In one study, Jeff Kwong of the Institute for Clinical Evaluative Sciences in Toronto and colleagues, evaluated the effect of the universal immunization program on influenza-associated health outcomes.

The researchers analyzed national and provincial data from 1997 to 2004 to compare changes in Ontario's flu outcomes before and after the program. In comparison with other Canadian provinces, Ontario's universal vaccination program was associated with reductions in influenza outcomes including flu-related deaths, hospitalizations and visits to emergency departments and doctors' offices.

However, even with free flu vaccines in Ontario, only an estimated 38 percent of the overall household population reported receiving them suggesting better outcomes if more were vaccinated.

The study is published in the journal PLoS Medicine.