WHO foresees problems with pandemic severity index

May 13, 2009 (CIDRAP News) – A World Health Organization (WHO) official today signaled that the agency is stepping back from plans to develop a way to grade pandemic severity, because its experts believe severity will vary from place to place, making the development of a severity index difficult and its use impractical.

Sylvie Briand, acting director of the WHO's Global Influenza Programme, told reporters at a media briefing today that the agency's technical experts have discussed a severity index several times, and they understand that pandemic severity is a key piece of information that governments use in response planning. But even within the same country, severity can vary among regions and during different waves of illness.

"Having one indicator to describe all these varieties of situations was not very helpful," Briand said.

She said severity is based on three components: the virulence and transmissibility of the virus, the vulnerability of the population, and the capacity of a country to fight the disease. All three components can vary across countries and pandemic waves, Briand said. "This is why it's hard to have an index."

The WHO is gathering as much information as possible to help countries assess their vulnerability and fight the disease, she said. Instead of issuing a severity index, the WHO will base its guidance on a concept paper, issued on May 11, that outlines key severity issues and indicators that help countries assess their own vulnerability to the virus.

In the May 11 statement about severity, the WHO said the novel H1N1 influenza virus seems to be more contagious than seasonal flu, but typically causes "very mild illness" in otherwise healthy people. The statement also said that most people, with the possible exception of older groups, are likely to have little or no immunity to the virus.

Briand repeated that the WHO pandemic alert phases refer to geographic spread and transmission patterns, but not severity. The WHO will continue to look at severity assessment. "In terms of linking, necessarily, phases with severity, let's see if it's useful, but it's probably not so useful," she said.

See also:

May 11 CIDRAP News story "WHO: H1N1 flu more contagious than seasonal virus"

May 11 WHO statement on pandemic severity assessment

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