The World Health Organization and the US were following a playbook of precautions developed over the past five years to prepare for the next super-flu. The WHO on Saturday asked all countries to step up detection of this strain of A/H1N1 swine flu and will reconsider on Tuesday whether to raise the pandemic threat level, in turn triggering additional actions.

A potential pandemic virus is defined, among other things, as a novel strain that's not easily treated. This new strain can be treated with Tamiflu and Relenza, but not two older flu drugs. Also, the WHO wants to know if it's easily spread from one person to a second who then spreads it again -- something US officials suspect and are investigating.

There is no vaccine against swine flu, but the CDC has taken the initial step necessary for producing one -- creating a seed stock of the virus -- should authorities decide that's necessary. Last winter's flu shot offers no cross-protection to the new virus, although it's possible that older people exposed to various Type A flu strains in the past may have some immunity, CDC officials said Sunday.

Worldwide, attention focused sharply on travelers.

"It was acquired in Mexico, brought home and spread," Nova Scotia's chief public health officer, Dr. Robert Strang, said of Canada's first four confirmed cases, in student travelers.

New Zealand said 10 students who took a school trip to Mexico probably had swine flu, and on Monday it said three students in a second group just back from Mexico probably have it as well.

Spanish authorities had seven suspected cases under observation. In Brazil, a hospital said a patient who arrived from Mexico was hospitalized with some swine flu symptoms. A New York City school where eight cases are confirmed will be closed Monday and Tuesday.

China has asked people entering the country from the virus-hit areas to report flu-like symptoms to the authorities. Russia began planning to quarantine travelers arriving from flu-affected areas if they have symptoms. Italy, Poland and Venezuela advised citizens to postpone travel to affected parts of Mexico and the US.

Multiple airlines, including American, United, Continental, US Airways, Mexicana and Air Canada, are waiving their usual penalties for changing reservations for anyone traveling to, from or through Mexico, but have not canceled flights.

The US hasn't advised against travel to Mexico but does urge precautions such as frequent hand-washing while there, and has begun questioning arriving travelers about flu symptoms.

ChinaDaily Mobile News