Amid the rapid spread of swine flu in some countries, the World Health Organization (WHO) on Monday raised its pandemic alert level from Phase 3 to Phase 4, warning of a significant increase in the risk of a pandemic.

Following the advice and guidance of an emergency committee, WHO Director-general Margaret Chan decided to raise the alert level from the current Phase 3 to Phase 4, a WHO official told the media on a teleconference.

A raise to Phase 4 means the swine flu virus can cause sustained human-to-human transmission and "community-level outbreaks," indicating a significant increase in the pandemic risk, according to the WHO's six-phase alert system for a possible pandemic.

But raising the alert level does not necessarily mean a pandemic is considered inevitable, Keiji Fukuda, the WHO's temporary assistant director-general for Health Security and the Environment told reporters via a web press conference.

The new virus strain, a subtype of A/H1N1, has not been detected in swine or humans before. With little or no resistance from the human immune system, the strain has the ability to aggressively attack the body and become deadly.

WHO Director-general Margaret Chan has said containment is not feasible at this time and instead efforts should be focused on mitigation.

"Either closing borders or restricting trade would have very little effect of stopping the movement of the influenza strain but it would cause a great deal of disruption for countries," said Fukuda.

However, Fukuda urged people experiencing flu-like symptoms to delay travel and seek immediate medical attention.

In its third and last recommendation, the WHO chief considered that production of seasonal influenza vaccine should continue at this time, subject to re-evaluation as the situation evolves. As there are a number of parties involved, the WHO will facilitate the process needed to develop a vaccine effective against the A/H1N1 virus.

In Mexico, there have been 1,614 suspected cases of swine flu, including as many as 149 deaths. UN Secretary-general Ban Ki-moon on Monday noted that the deaths in Mexico were of particular concern because those who died were "young and healthy adults."

On Monday, the WHO said there were 40 confirmed cases of the swine flu across several states in the U.S.--California 7 cases, Kansas 2 cases, New York 28 cases, Ohio 1 case, and Texas 2 cases. No deaths have been reported.

Suspected or confirmed cases of swine flu were also reported in Scotland, Canada, New Zealand, Israel, France, Spain and Brazil.

According to a Monday statement from Margaret Chan, the WHO chief, "The decision (to raise the alert level) was based primarily on epidemiological data demonstrating human-to-human transmission and the ability of the virus to cause community-level outbreaks."

As further information becomes available, the WHO may decide to either revert to phase 3 or raise the level of alert to another phase, she said.

A raise to Phase 5 would indicate that a pandemic is imminent.

(Xinhua News Agency Apirl 28, 2009)