The World Health Organization raised its alert system to a step away from full-blown pandemic level on Wednesday, though new evidence circulating among scientists suggested that far fewer people have died from the swine flu in Mexico than earlier thought.
WHO officials said a pandemic is now inevitable, and urged countries to go on high alert against the new H1N1 virus, saying the bug's spread will affect "all humanity."
Yet an in-depth analysis of some of the 150 or so Mexican deaths linked to the flu found that few were actually caused by the new flu bug, suggesting a relatively modest fatality toll, said a well-placed Canadian infectious-disease expert.
The total of Canada's cases, meanwhile, jumped to 19 with three more each in B.C. and Ontario. Like the Canadian patients identified earlier, they were all described as having relatively mild infections.
Canada earned international praise at the same time for the scientific support it has lent to the WHO and Mexico, including agreeing to test on Wednesday a rush shipment of 200 Mexican blood samples at microbiology labs in Winnipeg.
In Geneva, Dr. Margaret Chan, director general of the UN agency, said she had decided to move the pandemic alert scale to phase five, one below the pandemic phase, while another WHO official said a pandemic is now inevitable.
Dr. Chan urged that the world work together to fight the virus, with affluent nations donating anti-viral medication for use by developing countries, which she said are always hit the hardest by such diseases.
"Influenza pandemics must be taken seriously precisely because of their capacity to spread rapidly to every country in the world," said the Canadian-educated official.
"This is an opportunity for global solidarity as we look for responses and solutions ... It really is all of humanity that is under threat during a pandemic."
Pandemic phase five denotes a novel virus that has shown sustained transmission between humans in at least two countries of a particular region - Mexico and the United States in this case.
Level six - the pandemic phase - involves such transmission in at least one additional country in another region.
Dr. Chan said, though, said the most important unanswered question about the virus - a combination of pig, bird and human flu genetics - was how severely it will affect people.
The close to 1,900 cases and 150 or more deaths linked by Mexico to the microbe have inspired much fear. But pathologists and other scientists are now thoroughly investigating those deaths through autopsies and tests, and uncovering a different picture.
Dr. Gerald Evans, head of the Association of Medical Microbiology and Infectious Disease Canada and a member of a federal pandemic-planning committee, said he was told that of approximately 25 "highly suspicious" deaths investigated, only seven were found to be a result of the swine flu.
"There was a lot of speculation and what seemed to be evidence there were dozens and dozens of deaths. Careful analysis showed these people likely died of something else, and not flu," he said. "That's really good news, and that would fit with what we've seen outside of Mexico."
Meanwhile, there are still only 26 lab-confirmed cases in Mexico.
Dr. Todd Hatchett, a microbiologist at Dalhousie University in Halifax who also advises the federal government on pandemic planning, said he, too, had heard that the Mexican death toll is being downgraded under further investigation.
Based on what is known about the new swine flu, it could either fizzle out totally, become more adaptable to transmission among humans yet less virulent, or become more adaptable and more dangerous, he said.
Many experts, though, are speculating that the new flu, even if it triggers a pandemic, will be no more serious than a regular seasonal strain, which can still cause as many as 4,000 deaths a year in Canada, mostly among the elderly, very young and immune compromised.
"A pandemic relates more to geography ... not severity," noted Dr. Lynora Saxinger, an infectious disease specialist at the University of Alberta Hospital.
Still, while the new flu might not be any more virulent or deadly than a regular seasonal variety, many more people could end up being infected because most have no immunity to it, said Dr. David Butler-Jones, head of the Public Health Agency of Canada.
He said his organization is already operating as if in pandemic mode, since Canada is among the nine countries with cases.
Dr. Chan, meanwhile, specifically praised work done by both Canada and the U.S. Centers for Disease Control in helping the WHO and Mexico.
On Wednesday, 200 samples from Mexico were flown in for testing at the public health agency's Winnipeg lab, after a telephone request on Tuesday night from the Mexican health minister. Mexico has no ability to conduct such tests itself, relying instead on this country and the States.
Canada is also at the forefront of efforts to produce a vaccine, with the Winnipeg labs trying to develop a "seed virus" that could be used as the basis for a vaccine, said Dr. Butler-Jones. Such an immune agent will likely not be available, though, for four to six months, experts say.
Meanwhile, Dr. Butler-Jones urged that ordinary Canadians - and even Mexicans - avoid wearing surgical masks to ward off the virus, saying they can produce a false sense of security that actually leads to more infection.