The World Health Organisation is expected to move quickly to designate a full pandemic -- at level 6 of its 6-point scale -- within days to reflect the continuing spread of swine flu among people who have not been to Mexico, including in Europe.
Margaret Chan, the WHO's director-general, on Wednesday night raised the world flu alert level from 4 to 5 and said: "It is really all of humanity that is under threat during a pandemic."
Echoing other infectious disease experts, and drawing on her experience fighting SARS and bird flu outbreaks as health director of Hong Kong, she said viruses such as the H1N1 swine strain needed to be closely watched in case they worsen.
"We learn from previous pandemics. Pandemic virus is precarious, unpredictable, and will take us by surprise," she told reporters at the WHO's headquarters.