21st centuries first flu pandemic declares The World Health Organization (WHO)

The World Health Organization (WHO) declared the first flu pandemic of the 21st century on Thursday, urging countries to shore up defenses against the virus which is "not stoppable" but has proved mainly mild so far.

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.

"This is a very important and challenging day for all of us. It is important because we will be raising our pandemic alert level to level 6," WHO Director-General Dr. Margaret Chan told reporters on a teleconference."At this time, the global assessment is that we are seeing a moderate pandemic."

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

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 a countries and it is not stoppable," Dr. Margaret Chan said. "Moving to pandemic phase six level does not imply we will see an increase in the number of deaths or very severe cases. "Quite on the contrary. Many people are having mild disease, they recover without medicines in some cases and it is good news," Dr. Margaret Chan said.