Gregory Hartl, a WHO spokesman, told reporters in Switzerland it was still too early into the outbreak to deliver any conclusions on the threat posed by the new flu strain.
"I think we would want to wait a while before making a definitive decision," he said.
On Sunday, Felipe Calderon, the Mexican president, said his country was "in a position to overcome" the epidemic.
"We have been able to hold or at least reduce the rate of propagation of the virus to contain the epidemic," he said.
"We won't cry victory, but we can look at resuming certain activities."
Mexican officials are expected to decide on Monday whether to extend a five-day nationwide shutdown or allow schools and businesses to reopen later this week.
Late Sunday Jose Angel Cordova, Mexico's health minister, said the official number of confirmed dead in his country from the virus - which apparently combines swine, bird and human forms of influenza - had been updated to 22, following new lab results.
"The evolution of the epidemic is in its declining phase," he said, two months after Mexican authorities first began reporting cases of an influenza-like illness.
"The national peak was between April 23-28."
Cordova said the number of confirmed cases was 590, including the 22 dead.
Another 101 deaths are being treated as suspected as having been caused by the virus.
Containment measures, including the public's use of face masks and regular hand-washing, had been effective in limiting the flu's spread, Cordova said.
But he cautioned that the government, medical authorities and citizens should remain vigilant in the epicentre of the global outbreak.
Nineteen confirmed in Mexico out of 473 suspected. One death in the United States
Countries with confirmed cases: Mexico, the US, Canada, New Zealand, Spain, Israel, Britain, Germany, Austria, Switzerland, the Netherlands, China, Denmark, France, South Korea, Italy, Ireland, Costa Rica, Colombia
Countries with suspected cases: Australia, Brazil, Chile, Norway, Guatemala, India
Annual influenza epidemics are thought to result in three to five million cases of severe illness and between 250,000 and 500,000 deaths around the world, WHO says
The spread of the H1N1 virus is also being closely watched after Colombia confirmed the first case in South America, where the flu season is about to begin.
Dr Richard Besser, the acting chief of the US Centre for Disease Control and Prevention, said there were 226 confirmed cases in 30 states in the country, with the flu spreading just as easily as regular winter flu.
He said the H1N1 virus was not displaying some of the traits associated previously with more severe flu but added "it doesn't mean we're out of the woods yet".
The WHO's global alert currently stands at phase five - signalling that a pandemic is imminent - while phase six would mean a pandemic, or global spread, was taking place.
In the Canadian province of Alberta officials quarantined about 220 pigs that became infected from a worker who recently returned from Mexico, in the first documented case of the virus passing from a human to pigs.
Dr Jon Andrus, of the Pan American Health Organisation in Washington, said the general view is that the current outbreak "is mild to moderate in severity".
"That is not to say that things cannot change very rapidly and very dramatically."
Al Jazeera's Mariana Sanchez, reporting from Mexico, said some Mexicans believe their government may have overreacted and may be trying to divert the nation's attention from other serious problems, such as Mexico's drug war.
Beyond the Americas, infections have, so far, been mild, but health officials have been taking precautions with officials in Hong Kong quarantining hundreds of people in a hotel after an H1N1 case was confirmed in the territory.
"These are discriminatory measures, without foundation"
Mexican foreign minister
Mexico has condemned the move, which came after a 25-year-old Mexican who arrived in China on a flight from Mexico was found to be suffering from the virus.
"We are especially worried about China, where Mexican citizens showing no signs at all of being ill, have been isolated under unacceptable conditions," Patricia Espinosa, Mexico's foreign minister, said.
It was unclear how many guests at the Metropark hotel were Mexican citizens.
"These are discriminatory measures, without foundation ... the foreign ministry recommends avoiding travelling to China until these measures are corrected," Espinosa said.
She also condemned China as well as Argentina, Peru, Ecuador and Cuba for suspending flights from Mexico due to the flu outbreak.