The holiday season is an ideal time for the spread of flu. (Misha Japaridze/Associated Press)

Although about 40 per cent of Canadians have been immunized against the H1N1 virus, people should not be complacent, federal health officials warned Tuesday.

"As we approach the end of 2009, it's tempting to think that perhaps, given the numbers, the pandemic's done. This is wishful thinking that can lead to complacency," Dr. David Butler-Jones, Canada's chief public health officer, said in Ottawa.

"I want to counter the complacency by emphasizing once again the spread of H1N1 is not over and it can come back … We're not done yet."

In the last scheduled news conference on H1N1 of the year, Health Minister Leona Aglukkaq and Butler-Jones highlighted Canada's pandemic preparation and response.

For the week ending Dec. 5, there were 370 hospitalized cases reported that week, down from 804 the week before. Of these, 83 were in intensive care units, compared with 139 the previous week. The number of reported deaths was 33 versus 56 the previous week, according to the Public Health Agency of Canada.

The holiday season is an ideal time for spreading the virus as people gather to celebrate, Butler-Jones noted.

Immunization rates vary from one-third to two-thirds depending on the jurisdiction.

Health officials in Newfoundland and Labrador are talking about "high 60s" and "high 80s" for school children being immunized, Butler-Jones said, while other areas are in the 25 per cent range.

Extra vaccine supply

No decision has been made on what to do with any leftover shots of the 50.4 million doses of vaccine that the federal government ordered, such as selling or donating supplies to other countries. Aglukkaq reiterated that a decision is expected early in the new year, but that vaccinating Canadians remains the priority.

Butler-Jones said it's surprising how similar the H1N1 pandemic virus is to the 1918 pandemic, in that young people are largely affected. But prevention, early recognition and treatment as well as sophisticated ICU care have kept the majority alive, which would not have been possible a few years ago.

Aglukkaq stressed the importance of dealing with facts and confirmed cases since the virus emerged in April, to avoid devoting resources where they may not be needed — an approach that was shared by the provinces and territories.

Meanwhile, in the U.S. on Tuesday, health officials said vaccine maker Sanofi-Aventis SA is recalling four lots of its pediatric H1N1 vaccine because it is not as potent as it should be.

There are no safety concerns, and children who received doses from the recalled lots do not need to be immunized again, the U.S. Centers for Disease Control and Prevention said.

The lots were discovered during quality assurance testing.

Swine flu vaccines from a different manufacturer, GlaxoSmithKline, are used in Canada.