A study that evaluated the Canadian province of Ontario's universal flu vaccine program found that the more people in a community who receive the vaccine, the more the community as a whole may be protected from the flu.
That could be because people who get the flu vaccine act as "roadblocks" that keep the virus from spreading further -- a concept called indirect protection or "herd protection."
Most other Canadian provinces, as well as the United States, offer targeted programs instead, recommending the vaccine only for high-risk groups such as children and the elderly. Whether a universal vaccine would provide even more indirect protection for those groups and others is "one of the burning questions in epidemiology," says pediatric epidemiologist Joanne Langley, of Dalhousie University in Nova Scotia.
In 2000, the Canadian province of Ontario introduced the world's first program to offer the flu vaccine to every citizen, free of charge. The government even set up clinics at places like shopping malls to encourage citizens to get the shot.
"You can go to your grocery store, or the mall, and the Public Health Unit will be there," says Jeff Kwong, a researcher at the Institute of for Clinical Evaluative Sciences in Toronto and lead author of the new study.
The study, published this week in the journal Public Library of Science Medicine, found that the program may have averted as many as 300 deaths, 1,000 hospitalizations and 200,000 doctor visits per year, on average, according to the Canadian Press news agency.
Kwong and his colleagues compared the rates of flu vaccination as well as flu-season hospitalizations, doctor visits, emergency room visits and deaths in Ontario to those in other provinces between 1996 and 2004.
The researchers found that in 1996, before the universal program started, 18 percent of the population received the flu vaccine in Ontario and 14 percent received it in the other provinces. Not all citizens took advantage of Ontario's free program, but by 2004 about 38 percent of Ontarians were vaccinated, compared with about 24 percent of the population in the rest of Canada.
Deaths, hospitalizations and doctors visits went down across the country during the study due to higher vaccination rates, but they fell the furthest in Ontario -- the province had 40 percent lower death and hospitalization rates, 55 percent fewer emergency room visits and 60 percent fewer doctor visits due to influenza than other provinces.
Interestingly, vaccination rates among the elderly -- those older than 75 -- actually rose more in other provinces than they did in Ontario during the study period, perhaps because Ontario's rates were high to begin with, and because other provinces also offered free vaccines to the elderly and other high-risk groups.
Despite this fact, though, death rates and other flu-related outcomes in the elderly still decreased more in Ontario than in other provinces. This could mean that the flu vaccine doesn't work as well in the elderly as it does in young adults -- something other studies have suggested -- or it could mean that the elderly in Ontario received "herd protection" because of the higher rates of vaccination in the general population there.
"Which is it?" Kwong asks. "Unfortunately with the data we have available it's not possible to answer that question."
Recently, Finland decided to implement a universal flu vaccine program, and Kwong says that other Canadian provinces are considering it.
"No one has taken the plunge yet, they've been waiting for evidence from Ontario," Kwong says.
Langley says that she hopes that other governments will design their universal vaccine programs to include ongoing evaluation, something that the Ontario government didn't do because of budget constraints.
The current study "used the best design they could given the available data," she says. But, she adds, researchers could answer more questions if "other places would collect data a little more comprehensively."