TORONTO (Canadian Press) -- Details of who H1N1 is sending to hospitals and who it is killing show how different this flu virus is from seasonal influenza, the head of the Public Health of Canada said Wednesday.

Dr. David Butler-Jones said that where seasonal flu mainly kills the elderly, the pandemic virus is taking its worst toll on those far down the age spectrum.

"Those most seriously affected by H1(N1) are 23 to 45 years younger than what we see with seasonal flu," Butler-Jones said during a media briefing.

To make the point, he compared data on hospitalizations, intensive care unit admissions and deaths caused by H1N1 to those seen during the 2007-08 flu season, using the latter as a proxy for seasonal flu in general.

Butler-Jones used median ages -- the midway point between the youngest and oldest person affected -- to draw the comparison.

As of Nov. 21, the median age of a person hospitalized with H1N1 in Canada is 26 years old. That's 45 years younger than the median age of people hospitalized during the 2007-08 flu season, he said.

And the median age of people admitted to ICUs in the country is 45 years old -- 23 years younger than the median age of 68 seen in the 2007 flu season.

The median age of Canadians who have died from H1N1 infections is 54 years old, compared to the median age of 82 from that earlier flu season.

To date 329 people have died from H1N1 infections. About two thirds of them have had medical conditions that increased their risk of death, but one third did not.

Butler-Jones, Canada's chief public health officer, said children under five years old have had the highest rate of admission to ICUs with this flu, followed by adults 45 to 64.

He warned it is too soon to know if Canada is past the peak of this wave of infection, though it appears that there has been a plateauing of transmission in most parts of the country.

Still, with likely more than half of Canadians still susceptible to the virus, a lot more people will become ill - and some will die - before H1N1 runs its course, Butler-Jones said, reiterating his plea for Canadians to get vaccinated.

"Coming down the mountain can be just as treacherous as climbing it," he said. "During the first wave, as many cases occurred after the peak as before it."

Copyright 2009 The Canadian Press