GENEVA - The World Health Organization warned on Friday against a false sense of security from waning and apparently mild outbreaks of H1N1 flu, saying the worst may not be over.

WHO Director-General Margaret Chan, who raised the United Nations agency's pandemic alert to the second-highest level, said there remained great uncertainty about the strain that could pose particular threats in Southeast Asia.

We are meeting at a time of crisis that could have global implications, she told an intergovernmental meeting on pandemic preparedness at the WHO's Geneva headquarters.

The meeting is tackling the sensitive question of virus sharing, in which countries provide biological specimens to the international community for use by pharmaceutical companies and vaccine makers who are formulating jab ingredients.

At the height of fears about bird flu, Indonesia had refused to share H5N1 virus samples without guarantees that any vaccines developed from them would be made available to poorer countries at an affordable price.

GlaxoSmithKline, Sanofi-Aventis, Novartis, Baxter International and other pharmaceutical companies others are awaiting WHO guidance about whether to start mass-producing vaccines to fight H1N1, which may force them to cut production of seasonal flu shots.

Chan said she would make a recommendation soon about the appropriate balance between the types of jabs.

We are moving on two tracks to ensure some security for seasonal vaccine and at the same time kick-starting early scientific work for pandemic vaccine, she told the session.

MILD SYMPTOMS

The WHO chief commended countries with H1N1 infections for their timely sharing of samples for risk assessment and making seed vaccine, saying that starting point for larger production of jabs could be ready by the end of this month.

And another top official, acting WHO director-general Keiji Fukuda, said there had been rapid, widespread sharing of specimens to date.

Participants in the two-day WHO meeting are seeking to reach agreement on standards for transparency, trust, and sovereignty related to virus sample sharing, an issue that is also expected to dominate next week's annual World Health Assembly in Geneva.

I hope the end result is something really balanced that we can use for a long time, Fukuda said.

According to the latest WHO count, some 7,520 people in 34 countries have been infected with the strain that is a genetic mixture of swine, bird and human viruses. Belgium was the latest addition to that official tally.

Mexico has experienced 60 deaths from the virus that has also killed three people in the United States, one person in Canada and one in Costa Rica.

Most patients infected with the flu, which spreads like the seasonal flu through sneezes, coughs and air droplets, have experienced mild symptoms and some appear to be asymptomatic.

Antiviral drugs such as Roche's Tamiflu and GlaxoSmithKline's Relenza are effective against the H1N1 strain. At present, however, the majority of people catching it are able to recover without drug treatment.

The WHO's pandemic alert scale represents its views on the way a virus is spreading, not the severity of its effects.

Evidence that H1N1 flu is spreading in a sustained way in communities outside of the Americas would prompt Chan to push the global alert to the top of the six-point scale and declare a full pandemic is underway.

The two European countries with the highest concentrations of cases are Spain with 100 and Britain with 71.

The virus has made a much smaller impact so far in Asia, with 7 infections in New Zealand, 4 in Japan, 4 in China and Hong Kong, 3 in South Korea and 2 in Thailand. No cases have been reported in Africa and Israel is the sole Middle Eastern state with WHO-confirmed infections, with 7.

Financial markets have already shrugged off fears about a possible pandemic, and most people have returned to normal routines, with schools re-opened in infected areas.

But Chan stressed that important risks remain.

She said the WHO is closely watching parts of Southeast Asia that saw large outbreaks of H5N1 avian flu -- a virus that can be deadly when it passes from birds to humans, but has not spread easily between people to date.

A mixture of H5N1 and H1N1 viruses could have a big impact, she said, while stressing: I am not saying it will happen.

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