The head of the World Health Organization (WHO) on Friday again warned governments of the danger and unpredictability of the A/H1N1 influenza virus, and called on them to adjust their countermeasures according to the changing patterns of the disease.

"This is a very contagious virus. We expect it to continue to spread to new countries and continue to spread within countries already affected," said Dr. Margaret Chan in closing remarks to the 62nd World Health Assembly (WHA).

"In cases where the H1N1 virus is widespread and circulating within the general community, countries must expect to see more cases of severe and fatal infections," she said.

She also urged the international community to watch carefully the behavior of the H1N1 virus as it encounters other influenza viruses circulating during the winter season in the southern hemisphere.

The current winter season in the southern hemisphere gives influenza viruses an opportunity to inter-mingle and possibly exchange their genetic material in unpredictable ways, she said.

The WHO director-general noted that measures on multiple levels have been launched, and the world "cannot go any higher" on this.

"For the first time in history, we are watching the conditions conducive for the start of a pandemic unfold before our eyes," she told delegates to the annual WHO meeting.

But given the highly unpredictability of the future evolution of the disease, the world faces such a tough issue as to how long their preparedness and surveillance measures can sustain.

"The answer depends on the situation, the capacities, and the risks in each individual country, and even in different areas within a country," Chan said.

"WHO cannot, at this point, solve the dilemma through universal guidance. Countries should adjust their responses in line with the changing patterns of the disease," she said.

The WHA is the supreme decision-making body of the WHO. The assembly is usually held in Geneva in May and participated by health ministers of the organization's members.

Major topics discussed at this year's assembly included the world's preparedness for a possible A/H1N1 pandemic and the equal sharing of virus samples and access to vaccines.

(Xinhua News Agency May 23, 2009)