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With a few countries in the Southern Hemisphere reporting a dramatic jump in swine flu cases, the World Health Organization is inching closer to declaring a full-scale, phase 6 pandemic. But WHO, acknowledging that its phasing system needs fine-tuning as it relies only on geographic spread of the novel H1N1 virus, soon plans to institute a severity index to make its warning system more useful to member countries. WHO also wants to provide more tailored guidance to individual countries to help them respond appropriately.

As of 2 June, 64 countries have reported nearly 19,000 confirmed cases of swine flu to WHO, including 501 from Australia, which now has the widest detected spread of the disease outside of North America. At a press conference today, Keiji Fukuda, WHO's assistant director-general, characterized Australia, Japan, the United Kingdom, and Spain as countries “in transition” from limited to sustained community spread of the virus. “Globally, we believe that we are at phase 5, but are getting closer to phase 6,” said Fukuda.

A phase 6 alert requires sustained community spread in two WHO regions, and some epidemiologists contend that has already occurred. But WHO, following criticism from member countries that declaring phase 6 could cause undue alarm about a virus that appears no more dangerous than seasonal flu strains, has been reluctant to declare this a full-scale pandemic. Yesterday, however, WHO consulted with influenza experts and public health officials from 23 countries who backed the continued use of a phasing system based on geographic spread of the virus. To improve its usefulness, the consultants also encouraged WHO to “modify this kind of movement to phase 6 with assessments of severity,” said Fukuda.

Severity is tricky to define as it includes everything from the virulence of a particular influenza strain to the vulnerability of a particular population and its ability to respond, Fukuda said, which means it can differ from place to place. “We will build flexibility into the assessments of severity,” he said. One possibility he said is to develop a three-point scale for severity that is country specific. So WHO might decide that one country is at phase 6, level 3, while others are at phase 6, level 1. “The trick is not going to be so much coming up with the three levels of severity, but it’s really how to do it in a way which can be implemented across a lot of different countries,” he said, noting that the levels might change over time.

Currently, Fukuda said the severity level of the global epidemic is “moderate.” Much uncertainty still remains about the number of people with serious illness, he said, and it’s clear that the novel H1N1 can kill perfectly healthy people. “We do have some hesitation in calling such an infection 'mild,' ” he cautioned. And WHO remains acutely concerned about the spread of the virus in the Southern Hemisphere, which is cooling down as it enters winter, the season that typically allows influenza viruses to thrive.