The WHO raised its pandemic alert level for the swine flu virus to phase 4, indicating a significantly increased risk of a pandemic, a global outbreak of a serious disease. Another source stated the level was phase 5.
The last such outbreak, a "Hong Kong" flu pandemic in 1968, killed about 1 million people.
Although the new flu strain has so far killed people only in Mexico, there were more than 40 confirmed cases in the United States, including 20 at a New York City school where eight cases were already identified.