WHO Considers Revising Definition of "Pandemic"

Responding to mounting confusion, the World Health Organization (WHO) has sent the definition of a full-scale, phase 6 influenza “pandemic” to the rewrite desk. But no formal revisions have been made yet, leaving the old definition in place, and that says a phase 6 alert should be triggered if two regions of the world have sustained community spread in humans of an animal or animal-human hybrid of a flu virus.

On 29 April, WHO raised the pandemic threat level from 4 to 5, citing sustained community transmission in the U.S. and Mexico. At the same time, WHO said phase 6 was “imminent” and would be declared if the same type of spread appeared in a second region of the world. But at a press conference today, Keiji Fukuda, WHO's assistant director-general, said that representatives from several countries who attended the World Health Assembly in Geneva this week criticized the current phasing system, which relies solely on geographic spread without regard to severity of disease.

Fukuda said WHO agreed with the countries that the phase system needs to more accurately reflect the impact the virus is having on populations. Fukuda also said WHO might bump up the alert to phase 6 if the virus started to spread significantly in the Southern Hemisphere, including South America and Africa, even without causing severe disease.

To clarify this confusing potential revision of the definition of phase 6, ScienceInsider asked whether WHO would declare a pandemic right now if the virus were the much deadlier H5N1 that causes avian influenza. “Even if it were H5N1, we would still be looking for clear evidence of widespread community outbreaks going on in countries in multiple regions,” said Fukuda. “This is still a situation that we have not seen yet.”

Fukuda did not know when WHO would craft a new definition of phase 6 and said it was not trying to “change the rules” but wanted to adapt to the situation. “What is the value of these phases?” asked Fukuda. “These kinds of tools are really there to help countries prepare themselves.” For the most part, he said, that has happened, and he stressed that WHO must remain flexible. “There is nothing like reality to tell you whether something is working or not,” said Fukuda.