Canada has lifted its travel advisory to Mexico, the epicenter of the global H1N1 virus, as the federal government says Canadians are not at any additional risk in the country due to the strain's spread in Canada.

The Canada Border Services Agency will keep on checking travellers for signs of the flu, however.

But specific-travel measures such as distributing health alert notices to passengers on Canadian flights to Mexico, and having quarantine officers meet direct flights from Mexico to Canada, will be ceased.

Canada's top public health officer says the H1N1 strain's spread appears to be decreasing as the flu season is ending.

"It looks at this point like we're over the worst of it in Canada for this season," Dr. David Butler-Jones told reporters Monday

"But, again, I'm going to hedge my bets on that because we're watching very closely and it's still within the incubation period of previous cases, so you could see a second spike.

"But, so far, we've not seen that ... and the peak does appear to be -- in all three countries, actually, Mexico, the United States and Canada -- largely toward the end of April, beginning of May."

There have been more than 520 cases and one death linked to the H1N1 virus in Canada.

No plan to raise alert level: WHO

The head of the World Health Organization said Monday she has no immediate plans to raise the H1N1 alert level from Phase 5, while officials in New York City say an assistant principal has died from the virus.

WHO chief Dr. Margaret Chan said the epidemic, which has sickened nearly 9,000 people in 40 countries, is in a "grace period," but told the agency's annual assembly that she could not speculate how long the period will last.

"No one can say whether this is just the calm before the storm," Chan said.

Officials around the world are concerned that the virus continues to spread easily between people and countries.

Chan acknowledged that the virus "has great pandemic potential," but would not say if or when she would raise the alert level to Phase 6, which would signal a pandemic.

According to Chan, the concern now is that the H1N1 virus could become more dangerous if it mixes with other flu strains.

She said the virus has spread to the Southern Hemisphere, where it could combine with other strains that are currently circulating there.

Or it could mix with bird flu, which is more deadly but less easily passed between humans.

Chan announced her decision despite calls from Britain, Japan and China, among other countries, that the agency change the framework it uses to decide how and when to raise the alert level.

Officials said the agency should consider information such as how many fatalities the virus has caused when deciding whether to declare a pandemic.

The WHO currently raises alert levels by how widespread a disease becomes.

Declaring a pandemic would likely lead to massive economic ramifications, as such a move would most certainly be followed by travel and trade restrictions.

"We need to give you and your team more flexibility as to whether we move to Phase 6," British Health Secretary Alan Johnson told Chan.

Officials raised concerns at the WHO's annual meeting, a five-day event attended by health authorities from the 193 member nations.

In addition to discussing the alert level, the meetings will also cover the issue of whether to ask manufacturers to begin work on a vaccine specifically for the H1N1 virus.

As of Monday, Chan said the agency had not issued such a request to manufacturers and warned countries against wasting their current stores of medical supplies.

"Manufacturing capacity for antiviral drugs and influenza vaccines is finite and insufficient for a world with 6.8 billion inhabitants," Chan said. "It is absolutely essential that countries do not squander these precious resources through poorly targeted measures."

Seventy-six people worldwide have died of the virus, the most recent being New York City assistant principal Mitchell Wiener.

Wiener, 55, died Sunday night after being in hospital for five days. He is the first person in New York to die of H1N1, but officials are trying to determine if he had underlying health problems that may have contributed to his death.

On Monday, Britain, Spain and Japan all reported new cases of the H1N1 virus, with Japan recording the most dramatic increase.

Japanese officials said that the number of patients with the virus jumped over the weekend from four to 130, many of them high school students in the western cities of Hyogo and Osaka.

There are 496 confirmed cases of the virus in Canada.

With files from The Associated Press