The World Health Organization (WHO) today raised the alert level for the H1N1 flu virus to Phase 6, signaling the first influenza pandemic of the 21st century.

The decision to go to the highest warning level is the first such declaration by WHO since 1968, when a strain known as Hong Kong flu broke out and killed about one million people.

WHO Director Margaret Chan says, “This pandemic will be of moderate severity, and we know from experience that severity can vary on many factors from one country to another.”

The H1N1 flu strain has been of moderate severity, but its continuing spread resulted in it being proclaimed a pandemic.

Phase 6 suggests by definition that a new strain of influenza to which most people appear susceptible is spreading in at least two regions of the world. “Community transmission” of the novel strain of flu beyond Mexico, the United States and Canada has been clear for several weeks.

WHO reports there have been 27,737 cases of influenza A infection in 74 countries with 141 deaths.

WHO’s reluctance to move to the pandemic designation is due to fears it would alarm consumers and trigger a panic. Adding to the reluctance has been evidence that the H1N1 strain is far less virulent than most experts expected the next pandemic to be. Most persons recover from the infection without specific medical intervention.

The Centers for Disease Control and Prevention says the new flu strain has infected more than 13,000 people in all 50 states and killed at least 27.