The Journal of the American Medical Association reports that in Canada young adults became critically ill very quickly.

Multiple organs failed and patients needed prolonged ventilation.

A separate study from Australia found "ECMO" pumps, which pump oxygen into the blood, increased survival rates for flu patients with respiratory failure.

In Mexico, where the outbreak started last spring, a third study reports a 40 percent fatality rate among young patients.

The United States is pushing the H1N1 vaccine to fight the spread of the virus, but experts say no one, not even health care workers, should be forced to take it.