Swine flu alert

Margaret Chan, director-general of the WHO, made the decision to raise the alert level following a four-hour meeting of the organization's emergency committee. The body stopped short however of recommending restrictions on travel.

Acting WHO assistant-general for health, Keiji Fukuda, said at a press conference following the meeting that the heightened alert was a "sign of a step towards pandemic influenza but a stage that says we are not there yet."

Fukuda 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 community outbreak.

The Geneva-based United Nations agency recommended that governments focus on mitigation and prevention, rather than containment, given that the H1N1 virus had already spread quite far geographically.

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

Virus spreads

In Mexico, the likely death toll from the virus now stands at more than 150. Authorities have taken the step of closing schools across the country until May 6 in a bid to stop the spread of the disease, which has reportedly infected more than 1,600 people there.

In the European Union, Spanish authorities confirmed the first case of swine flu in the 27-nation bloc on Monday - a 23 year-old-man who had just returned from Mexico harbors the new viral strain, but otherwise appears healthy.

The EU has also called for an emergency meeting of health ministers and advised against non-essential trips to areas where the deadly virus has surfaced.

In Spain, some 20 people are under observation, while dozens of suspected cases have cropped up in the UK, Sweden, Denmark, Switzerland, France and Italy.

Also on Monday, two cases in the UK were confirmed. The victims had recently returned from a holiday in Mexico. The British government has advised against non-essential travel to Mexico.

In the US, more than 40 cases have been confirmed, though none have been fatal. Nearly all the cases outside Mexico have been deemed mild.

German tours cancelled

German Health Minister Ulla Schmidt said it was impossible to predict the severity of the threat posed by swine flu.

"No one can exactly calculate the risk here. There could be a worldwide flu wave," she said in Tuesday's edition of the German daily newspaper Bild.

However she stressed that Germany was well-prepared to deal with a potential outbreak here. "We have an elaborate plan in place in the event of a pandemic, everyone from the federal government to the states and all the health authorities know exactly what to do in the event of a crisis," she said.

German authorities have also advised cabin crews arriving at Frankfurt's international airport from Mexico or other swine-flu-affected areas to report any sick passengers.

Germany's largest tour operator TUI has suspended all trips to Mexico City, but says trips to other parts of Mexico will continue.

European Commission chief Jose Manuel Barroso said European authorities would remain vigilant.

"We will continue to assess the information we are getting from the experts, evaluate the potential danger and decide together with member states on the measures to take," he said.

Virus analysis

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.