The H1N1 virus is now responsible for a total of at least 1,154 deaths since it emerged in Mexico and the United States in April and later developed into a global epidemic. Most of the deaths are in the Western Hemisphere.
WHO said on Tuesday that laboratory confirmed cases of the disease have now reached 162,380. It says this number is likely a low estimate because hard-hit countries are no longer testing all the people with flu symptoms.
WHO spokeswoman Fadela Chaib said "nobody knows" how many people are infected in the 168 countries and territories with cases.