09/19/2011 12:00 EDT | Updated 11/19/2011 05:12 EST

An ounce of prevention: study suggests flu shots keep little kids out of emerg

TORONTO - As provinces and territories get ready to roll out their annual flu shot programs, new research reinforces the idea that vaccinating little kids could significantly reduce hospital visits during flu season.

The study compared emergency department visits to children's hospitals in Boston and Montreal before and after the United States adopted a policy of recommending flu shots for kids aged two to five years old.

Emergency room visits for flu-like illness in the two locations had tracked pretty closely in the years before the policy shift, which came into effect for the 2006-07 flu season. But after the policy change, emergency room visits for kids of this age at Children's Hospital Boston dropped by 34 per cent when compared to those at Montreal Children's Hospital.

"It's pretty substantial," lead author Anne Hoen said of the effect found by the study, published Monday in the Canadian Medical Association Journal.

"It means a lot of kids are being protected and staying out of the emergency department due to influenza. And I think it's great evidence that getting your flu shot is a good way to protect yourself and also reduce illness in the community."

The team used the Montreal hospital as a comparator because Quebec did not recommend flu shots for children aged two to five at the time. In fact, it still doesn't. The province provides free flu shots for children aged six to 23 months. (Children under six months aren't vaccinated against flu.)

In reality, the authors cannot say for sure that the difference they saw was due to flu shots. This type of study cannot offer proof positive that an effect seen was caused by the intervention being examined; it can only suggest a relationship.

As well, the researchers didn't have breakdowns on what percentage of children in each city got flu vaccine in the years studied.

And U.S. national data suggest early in the life of the new policy plenty of American parents were not heeding the advice to get their children vaccinated against flu. Data for the 2008-09 flu season that were published by the U.S. Centers for Disease Control suggested only 32 per cent of kids aged two to four and 21 per cent of children aged five through 17 got a flu shot that year.

Still, senior author Dr. John Brownstein — a Montreal native who along with Hoen works at Children's Hospital Boston — said the team analyzed the data in such a way to try to rule out other factors that might have accounted for the finding, including differences in the severity in the flu seasons in the two locales.

"It's really mind blowing. And we had trouble processing that finding as well," Brownstein admitted. He said they tried "every which way" to disprove the effect, but "nothing could take away that finding."

Dr. Jeff Kwong, a Toronto-based researcher who has studied the impact of Ontario's universal flu shot program, found the study persuasive.

"It's very highly suggestive that there is an effect," Kwong said, though he suggested data comparing more than two locations would make an even stronger case.

The study also suggests the benefits of giving flu shots to kids in this age group may extend beyond the kids vaccinated. There were also smaller declines in emergency room visits for children aged five to nine and 10 to 18 when the Boston hospital's numbers were compared to those of the Montreal Children's Hospital.

Neither of the older groups of children was covered by a flu shot recommendation at the time in the United States. But it is widely believed small children play a key role in introducing and spreading flu within households, because they are more susceptible to it. The declines among older children may reflect the fact that with fewer little kids getting severely ill, their older siblings might have stayed healthier too.

The study comes as provinces and territories are getting set to begin the annual task of vaccinating against the flu.

Each jurisdiction has its own program, so start dates vary across the country, from the first of October in Ontario to early November in Quebec.

All provinces offer free shots to at least a proportion of their residents — people deemed to be at the highest risk of getting severely ill if they contract the flu.

And an increasing number of provinces and territories are offering free flu shots to all. Where Ontario's universal flu shot program was a first for Canada — and the world — in 2000, now Alberta, Saskatchewan, Manitoba, Nova Scotia, Yukon, Nunavut and the Northwest Territories all provide flu shots for free for any resident over the age of six months.