As Mexican authorities ponder when and how to reopen businesses and schools, the virus spread to Colombia in the first confirmed case in South America, a fact which has worried health officials since the flu season is about to begin in the continent.
Mexico also found itself embroiled in a row with the Chinese government over its decision to quarantine more than 70 Mexican travelers in the country. Mexico's ambassador to China, Jorge Guajardo, told reporters that even the Mexican consul in Guangzhou was held briefly after returning from a trip to Cambodia.
Calderon described such measures as "unfair," adding, "because we have been honest and transparent with the world some countries and places are taking repressive and discriminatory measures because of ignorance and disinformation."
He did not mention China by name but Mexico's Foreign Relations Department released a statement later, saying that Mexico would send a jet to several Chinese cities "where Mexicans have expressed their intention to return to Mexico."
China's Foreign Ministry denied it was discriminating against Mexicans.
By Monday morning, the World Health Organization had confirmed 1,085 cases in 21 countries -- up from Sunday's totals of 787 people in 17 countries.
Mexico's Cordova said there have been at least 568 confirmed cases of the disease and raised the death toll in that country, believed to be the epicenter of the outbreak, to at least 22. In the U.S., the virus claimed the life of a toddler in Texas last month.
WHO epidemic and pandemic diseases spokesman Gregory Hartl said Sunday that though the current epidemiology in Mexico might show a slowdown, history must be considered when evaluating the virus' potential to come back.
"I also would like to remind people that in 1918, the Spanish flu showed a surge in the spring and then disappeared in the summer months only to return in the autumn of 1918 with a vengeance, and we know that killed eventually 40 to 50 million people," Hartl said. "So I think while tracing these kind of curves of activity -- increasing, decreasing activity -- we cannot lower our guard."
As for the CDC's analysis of the H1N1 virus, Besser said, "what we've found is that we're not seeing the factors that were associated with the 1918 pandemic, we're not seeing the factors that are, were associated with other H1N1 viruses, and that's encouraging."
But though officials are cautiously optimistic, whether the virus will reemerge when the typical flu season starts in the fall is still unclear.
"Every virus is new," Besser cautioned. "And what it will do is different. And so you're hitting a critical point: What will happen this spring and summer?"
He reiterated that the virus is spreading "quite easily," and that he expects to see reports of more confirmed cases in this country.
The WHO's current pandemic alert level stands at phase five, which "is a strong signal that a pandemic is imminent," according to the organization's guidelines.