Mexico City Thursday fully lifted all swine flu restrictions imposed on the sprawling metropolis, as global health authorities puzzled over the origins and severity of the A(H1N1) virus.
"We can calm down now," Mexico City Mayor Marcelo Ebrard told a news conference, just weeks after the city was virtually shut down.
Mexico City was at the epicenter of the outbreak of swine flu which has now spread to 41 countries, infecting more than 11,000 people and leading to 85 deaths, according to the World Health Organization.
The capital's website dropped its five-level alert to the lowest level green on Thursday, signaling that schools, businesses and transport could function as normal, without extra health precautions.
The A(H1N1) virus has killed 78 in Mexico and infected 3,930 people, according to latest health ministry figures Thursday.
Even though the virus has now spread far overseas, WHO officials have so far resisted calling the outbreak a pandemic, remaining at level five which warns of an "imminent pandemic."
WHO Director General Margaret Chan, who first raised concerns about the dangers of the new multi-strain virus last month, has stopped short of declaring an all-out pandemic by moving to phase six.
During a meeting at the WHO's annual assembly Thursday, Chan listed the apparent mildness of the symptoms so far seen in swine flu patients as among the criteria that were prompting a cautious approach.
"One of the things we're not seeing is the same spread in the southern hemisphere that we've seen in the first three countries," a WHO official added.
There are concerns that the start of winter in the southern hemisphere, which includes much of South America, could enable the virus to mutate into a stronger, more virulent strain.
|A visitor wears a face mask as he visits the Imperial Palace in Tokyo.|
And new infections are still being reported, as the Philippines became the latest country Thursday to confirm its first case of the disease.
In the Philippines, a 10-year-old girl who flew in from the United States was diagnosed with swine flu, while Taiwan also confirmed its second case in a 22-year-old student returning from New York.
The number of new cases of the swine flu virus also soared in Japanese and Canada.
Japanese Prime Minister Taro Aso appealed for calm as the number of cases reportedly reached 292, including the third infection in greater Tokyo, the world's largest urban area.
In a government television advertisement, a female voice says "we do not have to fear this influenza if we receive early treatment." Premier Taro Aso then faces the camera and says: "I ask for your calm response."
In Canada, authorities said the number of swine flu cases had soared by more than 200 since the end of last week.
"Of the 719 cases, 13 have required hospitalization, which supports what we have seen so far in Canada, that the severity of the symptoms is more typical of seasonal flu," said Chief Public Health Officer David Butler-Jones.
"However, even with a mild flu, we need to remain vigilant in preventing illness and watching for changes in the virus."
Antoine Flahaut, an epidemiologist and head of the School of Public Health (EHESP) in France, told AFP that the technical elements were in place to move into the pandemic phase.
"But the WHO senses that recommendations which go with that are not adapted to the situation," he explained, pointing to air travel restrictions or advice to wear surgical masks.
Health officials have also been left puzzled over why the elderly appear not to be falling ill at the same rate, with most infections and deaths reported among younger people.
A study by the US Centers for Disease Control and Prevention (CDC) found Thursday that older people may have some kind of immunity to swine flu.
More than 64 percent of US infections have occurred among patients between the ages of five and 24, with just one percent of flu victims aged 65 or older.
One possible explanation is that "older adults might have been in contact a long time ago with a virus related to the one that we see now," said Anne Schuchat, interim deputy director for science and public health programs at the US Centers for Disease Control and Prevention.
"Adults might have some degree of pre-existing ... antibodies to the H1N1 virus, especially older adults over 60 or 65," she said.