An American report predicts almost 197 million Americans will catch H1N1 influenza by the end of December, with 77 million falling ill--2.6 million in the last week of October alone. What's more, vaccination will come too late to make much difference.

With the same assumptions applied to Canada, the delay in rolling out H1N1 vaccine may make it irrelevant to the impact of the disease here.

The report, by two Purdue University researchers, was published October 15 in Eurosurveillance. It predicts 63% of Americans will catch H1N1 by the end of the year. Up to 60% of those infected won't show any symptoms, but 40% - 77 million - will fall ill.

Although vaccinations are already under way in the U.S., the authors say the peak of the flu will occur at the end of this month, when 8 percent of all Americans will be infected in one week. This will be well before most vaccinated people have formed antibodies to the disease. At best, the authors estimate vaccinations will reduce the number of cases by 6 percent.

Applying the same model to Canada suggests that 21 million of us will catch H1N1 by New Year's Eve, with 8.4 million actually falling ill. At the peak of the outbreak, 1.6 million will be infected in a single week. Since Canadian vaccine won't be available until the first week of November at the earliest, it would seem unlikely to have much effect on the spread of the disease until late November or early December.

The Purdue researchers say that vaccination would reduce the number of infections by only 6 percent. This would reduce the number of deaths from swine flu by anywhere from 2,500 to 25,000 depending on the mortality rate.

Without any vaccination in Canada, a mortality rate of 0.05% to 0.5% would mean between 4,158 and 41,580 deaths. A 6% reduction in deaths thanks to vaccination would therefore save between 250 and 2,500 lives.

Applied to British Columbia's 4.4 million people, the Purdue model suggests 2.7 million of us will catch H1N1, and 675,000 will fall ill. Assuming a mortality rate between 0.05% and 0.5%, that indicates between 337 and 3,375 flu deaths by New Year's Day.

The test of the Purdue predictions will come in the next few weeks.

Crawford Kilian is a contributing editor of The Tyee.