As health officials conclude a meeting in Geneva on Wednesday on how best to try to limit the spread of a future flu pandemic among humans, experts remain divided on their chances of success.

The World Health Organisation (WHO) has convened 30 international specialists this week to revise its draft “containment strategy”, with the aim of producing a final version by the end of this month that they will then begin to put into action.

The aim is to “nip in the bud” the spread of any future flu strain that is transmissible between humans by using a “fire blanket” of antiviral drugs given to treat everyone in an area around an infection outbreak.

“We are not without defences, if we act collectively right now,” said Margaret Chan, the official in charge of WHO’s influenza response, at the opening of the meeting on Monday.

The questions are whether the strategy can work, what determines the likelihood of success, and whether it is worth diverting scarce public health resources to try.

The idea of containment gained credibility last summer, with the publication in the journals Nature and Science by UK and US academics of two different scientific models simulating an outbreak in Thailand. They argued that containment could work under certain conditions.

“We either contain an outbreak at source, or it will spread throughout the planet,” said Ira Longini, professor of biostatistics at the University of Washington, and author of the Science article, which suggested 100,000-1m doses of antivirals could be sufficient.

There was disagreement from the start, with Neil Ferguson from Imperial College in London, lead author of the Nature article, suggesting 2m-3m doses would be required to have any chance of success.

But both studies offered hope that for the first time, a flu pandemic could be held in check, rather than spreading uncontrolled around the globe.

Their conclusions gained momentum when Roche of Switzerland, the pharmaceutical group that makes Tamiflu, the principal antiviral drug, donated a stockpile of 3m treatments to the WHO. That has since been boosted with pledges of a further 2m, and initiatives to launch regional stockpiles, notably in Asia.

However, Marc Lipsitch from the Harvard School of Public Health and colleagues wrote in the Public Library of Science Medicine online journal more recently that the probability of successful containment was slimmer still.

Even if one localised outbreak were stopped, others were likely to follow, he argued, requiring large volume antiviral use each time.

“There’s a very good chance that some of the assumptions will be violated,” he said. For success, the containment models generally required an outbreak to not begin in a densely populated area, to be detected early, and to be accompanied by measures such as quarantining.

Mr Longini argued that the chance of pandemic flu mutation occurring more than once was slim, but conceded: “If there is a mild strain not well adapted to humans, there is a very good chance of stopping it. If it’s more aggressive, there is virtually no chance.”

He dismissed the likelihood that air travel restrictions – proposed by several countries – would prove effective, but suggested “social distancing”, such as school closure, could help limit a pandemic’s impact.

“Even if the pandemic cannot be stopped, public health interventions might buy time to allow countries to further strengthen their response systems, as well as accelerating the production of pandemic vaccine,” WHO said in a statement. “Even if there is a small chance . . . WHO has a responsibility to try.”

Additional reporting by Frances Williams in Geneva

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