UPDATE: NYC health authorities say at least eight cases of flu in Queens are probably swine flu (they eliminated types A and B) and two cases were confirmed today in Kansas City.

This is very, very serious, and I'm glad Mexican authorities are treating it as such. One of the key factors in a pandemic flu (a global outbreak) is a mutated strain for which no one has immunity, and of course no one has developed a vaccine yet:

April 25 (Bloomberg) -- The World Health Organization is set to declare the deadly swine flu virus outbreak in Mexico and the U.S. a global concern, potentially prompting travel restrictions, said a person familiar with the matter.

An emergency committee of the WHO in Geneva will declare the outbreak “a public health event of international concern” in a 4 p.m. teleconference today, said the person, who spoke on condition of anonymity because the meeting is confidential. In response, WHO Director-General Margaret Chan may raise the level of pandemic alert, which could lead to travel restrictions aimed at curbing the disease’s spread.

“These levels of pandemic alert are all signals for action,” said Malik Peiris, a professor of microbiology at the University of Hong Kong, who has studied influenza viruses for more than a decade. “Raising the level of alertness to influenza, especially in returning travelers, would be a relevant thing to do.”

Human-to-human spread of the previously unseen H1N1 swine influenza in Mexico and the U.S. is heightening concern that the virus may spark a pandemic. At least 68 people have died and more than 1,000 have fallen ill with flu-like symptoms in the Mexico City region in the past month, Jose Cordova, Mexico’s Health Minister, told reporters yesterday. The government has shut schools and distributed face masks.

Sari Setiogi, a WHO spokeswoman in Geneva, declined to comment on the agency’s response, saying it will depend on the outcome of today’s meeting.