Geneva - The World Health Organization (WHO) has raised its pandemic alert level for influenza one step to phase 4 in light of the developments of the swine flu outbreak, an official said Tuesday in Geneva. Margaret Chan, director general of the WHO, made the decision following an extradited meeting of the organization's emergency committee but did not recommend restrictions on travel.

The WHO's Keiji Fukuda said the heightened alert was a "sign of a step towards pandemic influenza but a stage that says we are not there yet."

Fukuda, assistant director-general for health security, said "it was not considered inevitable at this time" that the virus would become pandemic.

"The situation is fluid and continues to evolve, and we will monitor," he told reporters.

The decision was based on evidence indicating sustained human-to- human transmission but not a sustained threat of a community outbreak.

WHO recommended that governments focus on mitigation and prevention, rather than containment, given that the virus, dubbed A(H1N1), has already spread quite far geographically.

"Really, this virus is too widespread to make containment a feasible consideration," Fukuda said.

The WHO said Mexico has reported 26 confirmed human cases of infection with the same virus, including seven deaths. Canada has reported six cases, with no deaths, while Spain has reported one case with no deaths.

The United States had 40 confirmed cases, none fatal.

Nearly all the cases outside Mexico have been deemed mild.

The Geneva-based body said it was not recommending shutting borders or restricting travel at this time, except for people who were already ill.

Fukuda said the organization, along with national governments, need to pin down the nature of the new virus.

"This is a new influenza virus, so we don't know how this one will evolve and how diseases related to this will evolve," he said.

The WHO said it would try to facilitate production of new vaccines but that development would take several months at a minimum.

Fukuda did not rule out that his agency would further raise the alert level in coming days but said it was too soon to tell what would develop given the fast-changing nature of the information available.

There were still ongoing investigations into the spread pattern of the virus and the length of the spread chain as the flu is passed from one source to another. (dpa)