Posted on behalf of Declan Butler

The World Health Organization (WHO) is getting ready to move its assessment of the pandemic threat of swine flu from phase 5 to 6, the top level on its six-point scale, denoting official global pandemic status. Keiji Fukuda, WHO’s interim assistant director-general for health security and environment, said today that the world was “getting closer to phase 6.” Speaking from Geneva at the WHO’s weekly media teleconference briefing on the influenza A (H1N1) strain, Fukuda said that outbreaks in many countries in Europe, Asia and South America – including Australia, Japan, the UK, Spain and Chile – were “in transition, moving from travel-related cases to more established community types of spread.”

That puts them on the trajectory already followed by North American countries, where there is now substantial sustained community spread, making a pandemic inevitable. “You can’t get in the way of the spread of this virus,” said Fukuda, noting that the virus is now in 64 countries, with lab confirmed cases – the tip of the iceberg – at 18,965, and some 117 known deaths caused by the virus.

The WHO had recently come under pressure from several member states to hold off from declaring a phase 6 pandemic, by redefining this status to include an assessment of the severity of the disease, and not only its geographical spread. There are also concerns about the potential economic impacts of moving to phase 6, such as trade embargoes, culling of swine, and worries about eating pork.

But after WHO consulted some 30 experts from 23 countries at a meeting yesterday, the agency has decided to hold on to its geographical definition of phase 6, requiring evidence of rapid spread in more than one WHO region. At the same time, if it does move to phase 6, three subcategories would be used to give a rough indication of the clinical severity as the pandemic moves forward in the months to come. Trying to put estimates of severity at a global level is “a rather difficult job,” said Fukuda. Severity will vary, he pointed out, both nationally and sub-nationally, and so WHO will focus more on tailoring its guidance as to what steps individual countries need to take. (See When is a pandemic not a pandemic?).

But Fukuda added that he would “hesitate to call the virus mild”, describing it rather as “moderate” – the virus has been severe in some healthy young people, for example. He also pointed out that estimates of mortality are uncertain – see How severe will the flu outbreak be? – and that the virus is likely to reassort and mutate unpredictably over time. “The future impact of this infection has yet to unfold,” he said.