The World Health Organization will hold an expert meeting later this month to consider whether the swine flu pandemic's peak has passed, a senior official said Thursday.

WHO's emergency committee will give its verdict to U.N. health chief Margaret Chan on whether the global outbreak has entered a "transition period," the agency's flu chief Keiji Fukuda said.

"This is a period in which we consider that the pandemic is still continuing," but that the worst of the outbreak is over, he said.

WHO declared swine flu a pandemic last June, when it announced the virus had reached "phase six" on its alert scale — the agency's highest designation.

"The post-peak phase is different from phase six, but it indicates that there is ongoing pandemic activity," Fukuda said later in a telephone interview. "It is a movement toward the post-pandemic period."

The experts will consider what measures governments should take to continue monitoring and combating the spread of the disease, he said.

"We hope that the worst is over but you can't suddenly let down your guard," Fukuda said.

He said the exact date of the meeting had not yet been set.

There have been over 15,000 laboratory confirmed deaths worldwide since the swine flu outbreak began in North America last spring. WHO says the actual death toll is probably much higher, but a final figure won't be available for 1-2 years.

WHO experts will also examine whether to advise governments and drug companies to include the swine flu strain in future vaccines for seasonal influenza, a move Fukuda said was likely given that the H1N1 strain will continue circulating for some time.

Although infections have declined in the Northern Hemisphere lately, WHO says it is still receiving reports of new outbreaks elsewhere, including most recently in West Africa.