TORONTO - As Canadians start rolling up their sleeves for this year's flu shot, researchers are rolling out a new analysis of last year's flu season.
The study published Monday in the Canadian Medical Association Journal compares the first and second waves of the H1N1 pandemic, which initially hit Canada in April 2009.
In the second wave, which began Aug. 30, 2009, there were 4.8 times more hospital admissions, four times more admissions to intensive-care units and 4.6 times more deaths. But ICU admissions and deaths as a proportion of hospital admissions fell in the second wave, even though patients admitted to hospital were older and more of them had underlying conditions.
There was a 16 per cent proportional decline in ICU admissions and a six per cent proportional decline in deaths compared with the first wave, the study found.
The analysis also revealed that the impact on aboriginal populations and pregnant women was much less in the second wave, said Dr. John Spika, director general of the Centre for Immunization and Respiratory Infectious Diseases at the Public Health Agency of Canada.
"I guess it's reassuring from that perspective that the kinds of interventions that we tried to put in place, both in terms of early antiviral treatment and getting the vaccine available, quite likely had an impact there," said Spika, a co-author of the study.
Altogether, there were 8,678 hospital admissions related to the pandemic, including 1,473 admissions to intensive care. There were 428 deaths.
In the first wave, the highest incidence rates of hospital admission were in Manitoba, Quebec and Nunavut, according to the tally.
"Compared with the first wave, British Columbia, Alberta, the Maritimes, Yukon and the Northwest Territories experienced substantially higher rates of hospital admission during the second wave," the authors wrote.
"Overall, Quebec reported by far the most hospital admissions, whereas Ontario reported the most deaths."
Spika noted that public health officials "were out there promoting the fact that certain high-risk groups should get treatment early," so he hopes that as a result, they sought treatment earlier in the second wave.
In addition, he said health-care professionals were better set to rapidly diagnose and treat H1N1 infection.
"I think during the second wave there was a much broader consensus that when people came in with flu-like symptoms that they could begin using Tamiflu," he explained.
Officials originally didn't think the vaccine would have an impact for two to three weeks after someone received it, Spika indicated. But data suggest the adjuvanted vaccine -- which most people received -- may have provided a "pretty good immune response occurring even at seven days," he said.
"So I think the vaccine, although it would've been nice to have it even earlier, was playing a role here as well."
The importance of flu vaccines for pregnant women and severely obese people are better recognized as a result of the H1N1 experience, Spika added.
Dr. Fiona Smaill, an infectious diseases expert at McMaster University in Hamilton, Ont., said the analysis was "worthwhile and thorough."
"The authors interpret the improved outcomes in the second wave with public health interventions (vaccination) and this does go along with estimates from Ontario that the H1N1 vaccination program was worth the money," she said in an email.
Dr. Rob Fowler, a critical care physician at Sunnybrook Health Sciences Centre, said the knowledge that changes occur over time in a pandemic means we can't rely on early case findings and reporting, but must follow through and discover what happens over the broader duration of a pandemic.
He made the comment as experts convened Monday at the Critical Care Canada Forum in Toronto, where he was to moderate a discussion on H1N1 -- One Year Later.
"When people are in the midst of it, it's a scary time. But then when it does subside, it fades from the memory of certainly the public, the press, and to some degree the health-care system rather quickly as though we've conquered it," he said.
"But we know very well that it's only a matter of time before the next similar or dissimilar outbreak/pandemic will come about ... and we really do need to be prepared for the next one."
Heading into this year's flu season, Spika said H3N2 influenza A Perth is likely to be the primary virus circulating. It's contained in this year's vaccine, along with H1N1 A and influenza B Brisbane.
The H3N2 strain is not one that people would have received in previous years, he noted.
"So I would hope that our messaging is such that we're really encouraging those, particularly those at greatest risk for seasonal flu complications, to get their shot."
A new no-needle alternative has been approved for use in Canada this year -- the nasal spray vaccine by AstraZeneca called FluMist.
It contains a weakened flu virus and has been on the market in the United States since 2003. It can be used in those age two to 59 years of age, the drugmaker said in a recent news release.
Spika noted that FluMist is not licensed for use in pregnant women, and isn't recommended for people who have respiratory illnesses like asthma.
"With those caveats, I think the vaccine has been shown to induce a good level of immunity," he said.
"I think it's a very good vaccine. The downside to it from a public health program standpoint is it does have a fairly short shelf life, and I think jurisdictions are going to have to really think about the logistics of using the vaccine if they introduce it into their routine programs."
