from phase 4 to phase 5

WaPo | The World Health Organization took the unprecedented step yesterday of warning that the world is probably on the verge of a pandemic, as new cases of swine flu mounted, the first death was reported in the United States and the dangerous virus appeared to arrive just outside the nation's capital.

The WHO's action came after the agency convened an unusual "global virtual science meeting" involving several hundred experts and officials to help assess the situation. The agency raised the alert from "phase 4" to "phase 5" two days after elevating it for the first time because the never-before-seen virus was spreading in Mexico.

Saying influenza viruses are "notorious for their rapid mutation and their unpredictable behavior," WHO Director General Margaret Chan told reporters: "This is an opportunity for global solidarity as we look for responses and solutions that benefit all countries, all of humanity. After all, it really is all of humanity that is under threat during a pandemic."

The new alert level could prompt a variety of measures, including more intensive efforts to identify cases and stricter measures to prevent the illness's spread, such as discouraging or banning public gatherings.

With the virus now clearly being transmitted person-to-person in the United States, WHO officials said the outbreak appeared to be on a trajectory toward the highest alert level -- "phase 6" -- which is marked by sustained transmission in at least two regions of the world. That would mark the beginning of a pandemic -- a global spread of the virus.

"It's clear the virus is spreading, and we don't see any evidence of this slowing down at this point," said Keiji Fukuda, the WHO's interim assistant director general for health security and environment.

While there is a chance that the epidemic could stop on its own, officials said that such an outcome is impossible to predict and that governments around the world should plan for the worst.

"There may be a possibility that the virus will die out and stop, and that would be the best for us. But it can turn the other way. So the important point for us is to continue to maintain our vigilance and track its movement," Chan said. "Influenza pandemics must be taken seriously precisely because of their capacity to spread rapidly to every country in the world."