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 in Hong Kong.
"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.
Swine flu in Hong Kong has raised fears of a repeat of the 2003 Severe Acute Respiratory Syndrome (SARS) outbreak, when almost 300 people died and concern about the mysterious disease turned the metropolis into a virtual ghost town.
Chan managed Hong Kong's response to avian influenza and SARS during her nine-year stint as Hong Kong's director of health.
Top of the agenda for the WHO's meeting this week will be how to combat the swine flu pandemic in developing nations.
While the Americas still has the highest death toll from the virus, cases are expected to increase in the region as the northern hemisphere enters winter.
There are fears that poorer countries will not get enough vaccines, despite a pledge last week by the United States and eight other nations to make 10 percent of their swine flu vaccine supply available to others in need.
Developing countries are not only unable to produce the vaccine for the A(H1N1) flu virus but their people are more vulnerable to infection because of poverty, crowded living conditions and lack of healthcare, according to the WHO.
In the Western Pacific there are about a million people living in poor conditions without access to healthcare, WHO regional director Shin Young-soo told reporters Sunday.