BREAKING NEWS: WHO raises pandemic alert level from 4 to 5

The World Health Organization has raised the pandemic alert level for the swine flu virus from a 4 to a 5, signifying a rise in sustained human-to-human transmission of the disease.

"The biggest question right now is this: how severe will the pandemic be?" said Margaret Chan, director general of the WHO. 

At a press conference broadcast from Geneva, Dr. Chan both emphasized the "unpredictable" nature of the influenza virus, and described the spectrum of cases as ranging from "mild" to "severe." The more severe cases are being seen in Mexico, said Dr. Keji Fukuda.

Fukuda explained that on the WHO alert scale, levels of "5 and 6 represent periods of time when the virus is spreading from country to country and beginning to be established." The sustained human-to-human transmission of the virus in both the United States and Mexico -- two countries in one WHO region -- indicated the move to phase 5.

In terms of the likelihood of reaching a full-blown pandemic, Dr. Fukuda said "We think we are in the process of moving toward there... but we still need to see the evidence that we are there."

"Many of these cases are mild," Chan said. ""Many of these patients recover on their ow, without medicine -- but that does not mean we should be complacent."

Neither Chan nor Fukuda recommended that individuals should alter their behavior beyond guidelines that are already circulating internationally, such as maintaining personal hygiene. Rather, the change in alert level is a call to countries to make sure their pandemic plans are up to date, including laboratory capacity, surveillance procedures, and communications strategies, Fukuda said.