Keiji Fukuda, the WHO's top influenza expert, said the U.N. agency's six-phase system for declaring a pandemic had sown confusion about the flu bug which was ultimately not as deadly as the widely-feared avian influenza.

The reality is there is a huge amount of uncertainty (in a pandemic). I think we did not convey the uncertainty. That was interpreted by many as a non-transparent process, Fukuda said.

He was addressing a three-day meeting of 29 external flu experts called to review WHO's handling of the first influenza pandemic in 40 years.

LINKS TO DRUG COMPANIES

Critics have said the WHO created panic about the swine flu virus, which turned out to be moderate in its effect, and caused governments to stockpile vaccines which went unused.

Some questioned its links to the pharmaceutical industry after companies like GlaxoSmithKline and Sanofi-Aventis profited from producing H1N1 vaccine.

Kenya's delegation criticized the United Nations agency for failing to ensure that developing countries received a fair share of vaccines developed against the virus.

It is not fair to have new vaccines and medicines and then they are so expensive that most poor people in developing countries can't access them, Kenya's delegate said. This is not a situation that should be tolerated at all.

To date, 31 poorer countries including Afghanistan, Cuba, Kenya and Myanmar have received limited supplies of vaccine donated by drug companies and Western countries, via the WHO.

India's delegation suggested that in public health emergencies, patents on vital drugs should be lifted in line with the World Trade Organization's TRIPS agreement on intellectual property.

H1N1, which emerged in Mexico and the United States almost exactly a year ago, has killed 17,770 people in 213 countries, according to WHO, which declared a pandemic under way in June.

The WHO will need another year or two after the pandemic is declared over to determine a final death rate from the virus, which is certain to be much higher. The pandemic is still officially under way.

FEAR AND CONFUSION

The World Bank has estimated that countries have spent $4 billion to prepare pandemic preparedness plans and respond to the outbreaks, according to the U.S. delegation to the talks.

Influenza is a formidable and unpredictable opponent. The threat of a severe pandemic has not decreased, the U.S. delegate said.

The separate but highly lethal H5N1 bird flu virus -- which has killed 60 percent of those infected since 2003 -- injected a high level of fear about the next pandemic, Fukuda said.

It had been difficult to meet public demands for advice as the H1N1 virus spread quickly across borders and blogs generated speculation and criticism, according to the WHO official.

One big surprise had been that only one dose of vaccine was needed to provide immunity, whereas most planning had been built around two doses being required, he said.

This meant that some countries were left struggling with an oversupply of unused vaccines while poorer ones had little or no access to supplies.

Confusion about phases and level of severity remains a very vexing issue, Fukuda said, referring to the WHO's six-level scale for pandemics which takes into account the geographic spread of a virus but not its severity.

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