That sounds scary. But neither the H1N1 swine flu virus nor the disease it causes are any worse today than they were weeks ago.
The only thing that's changed is that the WHO now officially acknowledges that H1N1 swine flu is circulating in communities in widespread parts of the globe, and that all nations can eventually expect to see cases.
"This does not mean there is any difference in the severity of the flu. This is not, at this point, a flu pandemic that is anywhere as severe as the 1918 pandemic," said Thomas R. Frieden, MD, in his first news conference since taking over as director of the CDC.
The announcement also triggers the pandemic preparedness plans of nations not yet affected by swine flu. It will have little or no effect on the U.S., which since mid-April has been aggressively putting national pandemic plans into action.
"For all intents and purposes, the U.S. has been in a flu pandemic for some time," Frieden said. "But this means the virus is here and is here to stay, and we must prepare our response."
U.S. actions include mobilizing the national stockpile of flu medications; issuing guidance to families, communities, and health workers; holding regular news briefings; and, most dramatically, moving ahead rapidly with the development of a swine flu vaccine.
"Our key goals will be to find where virus is spreading and reduce its impact, particularly in those with underlying health conditions and in infants," Frieden said.
In making the WHO pandemic declaration, Chan warned nations that have not yet seen swine flu infections that the pandemic is coming. And she warned nations such as the U.S., where in some areas the first wave of the pandemic is subsiding, to remain vigilant for a second wave of infections.
Exactly how worried should people be? Keiji Fukuda, MD, WHO interim assistant director-general for health security and environment, said people should know that if they develop a fever and cough, the "vast chances are they are going to do well." But if serious symptoms develop, such as trouble breathing, it's time so seek urgent medical care.
"The average person should know about these things ... but definitely not get overly anxious about it," Fukuda said. "It is like most things in life: Understand it, put it in context, and go on with things."
The WHO could have declared a pandemic weeks ago when it became clear that H1N1 swine flu was spreading in communities outside North America. The WHO's official definition of a Phase 6 pandemic -- the highest stage of its pandemic alert system -- is community spread of a new disease in at least two regions of the world.