At least 100 people are now suspected to have died of the disease in Mexico.
The UN has warned the virus has the potential to become a pandemic, but said the world was better prepared than ever to deal with the threat.
Stocks of anti-viral medicines are being readied and travellers are being screened at some airports for symptoms.
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News Health Swine flu Pig flu H5N1 Pandemic Influenza H1N1 WHO Flu Mexico
Bird Flu