WHO declares first 21st century flu pandemic

The World Health Organisation declared an influenza pandemic on Thursday and called on governments to prepare for a long-term battle against an unstoppable flu virus.

The United Nations agency raised its pandemic flu alert to phase 6 on a six-point scale, indicating the first influenza pandemic since 1968 is under way.

"With today's announcement, WHO moves from an emergency to a longer-term response. Based on past experience, this pandemic will be with us for some months, if not years, to come," WHO Director-General Dr. Margaret Chan said in a letter to staff, a copy of which was obtained by Reuters.

People aged 30-50, pregnant women or people suffering from chronic conditions such as asthma, diabetes or obesity are deemed at highest risk, she told a news conference.

Countries from Australia to Chile and the United States are also reporting that the new virus, commonly known as swine flu, is "crowding out" seasonal flu, becoming the predominant influenza strain, she said.

For now the virus was "pretty stable", but Chan warned that it could still mutate into a more deadly form, taking on characteristics of the separate H5N1 bird flu virus circulating widely in poultry.

"So it is incumbent on WHO and all members to stay vigilant and alert for the next year or two or even beyond," she said.

WHO's top flu expert Keiji Fukuda agreed, saying: "When you're talking about pandemic influenza, you are talking about a marathon, you are not talking about a sprint."

Acting on the recommendation of flu experts, the WHO reiterated its advice to its 193 member countries not to close borders or impose travel restrictions to halt the movement of people, goods and services, a call echoed by U.N. Secretary-General Ban Ki-moon.

The move to phase 6 reflects the fact that the disease, widely known as swine flu, is spreading geographically, but does not indicate how virulent it is.

Widespread transmission of the virus in Victoria, Australia, signaling that it is entrenched in another region besides North America, was one of the key triggers for moving to phase 6.

NO SURPRISE

"This is not a surprise," Dr. Thomas Frieden, new director of the U.S. Centers for Disease Control and Prevention, told a news conference. "It is expected based on the data."

A unanimous experts' decision was based on an overall assessment in the eight most heavily hit countries - Australia, Britain, Canada, Chile, Japan, Mexico, Spain and the United States - that the virus is spreading in a sustained way in communities, according to Chan.

"Collectively, looking at that, we are satisfied that this virus is spreading to a number of countries and it is not stoppable," she said.