WHO says nations must remain on guard against H1N1 flu

GENEVA (Reuters) - Countries where the H1N1 virus appears to have peaked need to remain vigilant and prepare for a second wave of infections because the flu is so unpredictable, WHO Director-General Margaret Chan said Thursday.

"When you are over with the first wave, start preparing for the future," Chan told reporters after the World Health Organization raised its pandemic alert to phase 6 to indicate a flu pandemic is underway.

Officials said the move reflected the geographic spread of the virus but did not indicate the severity of the influenza (A) H1N1 pandemic. She said the WHO's global assessment was that the pandemic was moderate.

(Reporting by Laura MacInnis, Jonathan Lynn and Stephanie Nebehay, Writing by Michael Kahn)