The A/H1N1 influenza so far has spread to about 160 countriesand is still advancing, the World Health Organization said Friday.

WHO spokesman Gregory Hartl told a news briefing that the virus has killed about 800 people worldwide since it was identified in April.

The A/H1N1 influenza, which the WHO declared a pandemic in June, has so far been characterized by extremely mild symptoms in the overwhelming majority of patients.

Hartl said there are no signs of the virus mutating and becoming more deadly despite its fast spread.

"For the moment we haven't seen any changes in the behavior of the virus," he said. "What we are seeing still is a geographic expansion across countries."

The spokesman stressed, however, that the world should keep monitoring the virus and be prepared for any possible changes.

(Xinhua News Agency July 25, 2009)