The second wave of the H1N1 pandemic that swept the country in the fall of 2009 was "substantially larger" than the first, with more deaths and hospitalizations, national public health officials say in a new report.
From April 2009 to April 2010, officials recorded a total of 8,678 hospital admissions, 1,473 intensive-care admissions and 428 deaths linked to the H1N1 epidemic, a team of Public Health Agency of Canada researchers say in the study, published Monday in the Canadian Medical Association Journal. It is the first to fully document the impact of the infection at a national level.
The cases occurred during two distinct waves of the epidemic — one that hit in the spring into the summer followed by another outbreak in the fall — but there were 4.8 times more hospital admissions, four times more ICU admissions and 4.6 times more deaths in the second wave than in the first, the results showed.
Typically, transmission rates are minimal in the summer months and the flu arrived earlier in fall than usual, the report explained.
But the percentage of severe cases, including death and intensive-care, from all hospitalizations was lower in the second wave, the PHAC researchers from the Centre for Immunization and Respiratory Infectious Diseases noted.
"The second wave was substantially larger and although the patients admitted to hospital were older and more of them had underlying health conditions, a smaller proportion had a severe outcome. The differences are thought to be due mainly to public health and clinical interventions implemented between the first and second waves," field epidemiologist Melissa Helferty and her co-authors said in the report.
It suggests an increased awareness of identifying at-risk groups, use of medicine, earlier admission to hospital and targeted interventions for Canadians living in remote and isolated areas helped lower the percentage of severe cases the second time around.
The mass vaccination campaign, which was launched from Oct. 22 to Nov. 1, also "may have" played a role, she said.
Even for the most vulnerable groups — pregnant women and Aboriginal people — there was a decrease in the percentage of severe cases in the second wave, although they still made up a large portion of those hospitalized.
Nunavut, Manitoba and Quebec reported the highest rates of hospital admissions in the first wave while the Maritime provinces, Alberta, B.C., and the Northwest Territories were most affected in the second wave, although the virus had spread throughout the country by then.
Overall, Quebec recorded the highest number of hospitalizations and Ontario reported the most deaths.
Another H1N1 report released in October showed that pregnant women typically represent only one to two per cent of the population, but they accounted for up to 10 per cent of all hospitalized H1N1 patients, nine per cent of patients in intensive-care units and up to 10 per cent of patients who died.
The investigators, led by Toronto-based doctors, criticized the response of Canadian health officials to the H1N1 pandemic, citing confusion over vaccination procedures and the care given to groups most at risk of contracting the virus: the people it said ended up suffering the most.
They suggested communication between federal public health officials, frontline workers and patients must be improved.
Charlene Wiles, PHAC spokeswoman, said the agency's study will be used to continue to evaluate and to plan for response to future pandemics and other national health emergencies.