Time to rewrite the rules of the pandemic

Sunday, May 28th, 2006
WHO to rewrite pandemic staging descriptions in wake of Indonesian cluster

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(CP) - The World Health Organization plans to redraft the descriptions of its pandemic phases, a task triggered by the confusion provoked by the recent large cluster of human cases of H5N1 avian flu in Indonesia.

The acting head of the WHO's global influenza program says the rewrite will spell out more clearly how the agency thinks a novel influenza virus would behave during the different phases leading up to a pandemic.

The redraft should also help people understand why the WHO doesn't believe the Indonesian cluster - which killed seven of eight infected members of a family in at least three waves of illness - signifies a change in the level of pandemic risk.

"What we're hoping to do is clarify what are the differences between phases and make it more easily understood by everyone what we're actually looking for," Dr. Keiji Fukuda said in an interview with The Canadian Press.

"There's clearly so much confusion both about what is Phase X or what is Phase Y, how do we go from it, what is the role of the pandemic task force and what is the process for deciding whether there should be a phase change.

"And so I think that what we will try to do is address those issues specifically and get it posted on the web," said Fukuda, noting he hopes the work will be completed in the next week or two.

The worrisome Indonesian cluster - the largest to date and the first time person-to-person-to-person spread of the virus is believed to have taken place - has provoked calls from some quarters to change the global pandemic alert level to Phase 4 from the current Phase 3.

Before it could consider making that change, the WHO would have to convene a panel of experts - the task force Fukuda mentioned - to comb through the accumulated scientific data looking for evidence H5N1 viruses are becoming more transmissible to and among people and therefore pose a greater pandemic risk.

The task force would advise the WHO. But the final decision rests with the Geneva-based global health agency.

The current pandemic phasing document is a six-step ladder going from no known pandemic threat (Phase 1) to a full-blown pandemic (Phase 6). Many experts admit it's hard to see the difference between Phase 3 (no human-to-human spread or rare instances where a person has had close contact with an infected person), Phase 4 (small clusters of limited and localized person-to-person spread) and Phase 5 (larger but still localized clusters of human-to-human spread).

Fukuda agrees the descriptions of the phases are ambiguous, acknowledging that "it drives people crazy because we can't say precisely: 'Look for three of these or 10 of those or 13 minutes of this."'

The revised version will likely key in on the type of activity that allowed the virus to jump from one person to another - prolonged close contact with a sick individual or more fleeting or incidental exposure.

It's been known since the first H5N1 outbreak in 1997 that the former could trigger human-to-human spread. The latter, though, would be a signal of a significant shift in the virus's transmissibility - and would likely prompt serious consideration of a phase change.

"That's a little bit hard to describe for people. It's easier to say we're looking for 10 people or 15 people," Fukuda said. "But in truth, what we're really looking for is what's the kind of contact between the source of infection and the people who become infected."

Redrafting the language may pose challenges. After all, the emergence of a pandemic flu virus is an uncharted process, one which science has never had the capacity to watch.

"No one has a black-white answer because we've never done it before," said Lance Jennings, a virologist and epidemiologist at Christchurch Hospital in New Zealand who helped draft the current pandemic phasing document.

Exacerbating the situation is the fact that determining whether human-to-human spread has taken place is an inexact science. Most clusters to date have occurred in families, where cases almost invariably share experiences and exposures.

Unless the genetic blueprint of the virus takes on some signature changes, in many such cases it's almost impossible to say with certainty that the source of infection was another person, not an infected bird.

Still, infectious disease experts believe the scientific world will be able to tell when the pattern of transmission has sufficiently changed - though how quickly the change will be noted is anybody's guess.

"I think we'll know it when we see it," said Dr. Michael Osterholm, director of the University of Minnesota's Center for Infectious Disease Research and Policy, reaching for the famous phrase coined to describe pornography - "I can't define it, but I can tell you when I see it."

But that phrase, often cited by experts attempting to describe the next phases in the pandemic alert scale, highlights how challenging it may be to put into words a clearer picture of what the stages of an emerging pandemic might look like.

A lot rides on the process. Pandemic planning by governments and multinational companies is geared to the level of the global pandemic alert. An upward shift in the level kicks pandemic preparedness activity into higher gear.

"There are major multi-national companies in this world that are prepared to evacuate expats out of certain areas of the world if the staging goes from 3 to 4," noted Osterholm, who cautioned major U.S. business leaders in New York last week against tying responses too closely to the WHO pandemic staging document.

"To try to distil down the current status of where we're at is like trying to give the world economy a one number grade," he said, but added the phases are useful "to help us organize our thinking."

Fukuda agreed that changing the alert level would likely have a domino effect on international trade, travel and economies.

"It would be perceived as countries as a signal that something significant had changed," he said. "I think it's quite likely that we would see an increase of action in all areas. Certainly an increase in concern. Certainly there would be a lot of media attention. Certainly countries would probably really look at their pandemic planning . . . and try to identify what gaps that t - hey might fill. It's highly conceivable that it would have a big effect on travel."

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(CP) - The World Health Organization's current pandemic phase scale is divided into six stages. They are:

Phase 1 - No new influenza virus subtypes detected in humans. An influenza virus subtype that has caused human infection may be present in animals, but risk of human infection considered low.

Phase 2 - No new influenza virus subtypes detected in humans. However, a circulating animal influenza virus subtype poses a substantial risk of human disease.

Phase 3 - Human infection(s) with a new subtype occur, but no human-to-human spread, or at most rare instances of spread to a close contact.

Phase 4 - Small cluster(s) with limited human-to-human transmission but spread is highly localized, suggesting the virus is not well adapted to humans.

Phase 5 - Larger cluster(s) but human-to-human spread still localized, suggesting that the virus is becoming increasingly better adapted to humans, but may not yet be fully transmissible.

Phase 6 - Pandemic: increased and sustained transmission in general population.