Swine flu virus has not yet mutated into more serious disease: WHO

The vaccines for (A)H1N1 influenza produced so far have been very effective, WHO Director-General Margaret Chan said at the opening ceremony for the organisation's annual Western Pacific meeting.

"The virus can mutate any time. But from April to now, we can see from the data given to us by laboratories worldwide that the virus is still very similar (to the previous state)," Chan told reporters.

Ideally, three billion doses of vaccines could be produced worldwide annually, she added, noting that China had already begun to vaccinate people.

She also said the Hong Kong government could relax its measures against a swine flu outbreak "step-by-step", advising them in the long-run to focus resources on saving patients and reducing the number of serious cases.

Chan said that only high-risk patients such as the elderly, the obese and those with underlying illnesses would be severely affected by the disease.