The severity of a disease, as well as its geographical spread, could be used to determine whether an outbreak is labelled a pandemic, a leading WHO official has said.
The WHO set up a committee to assess its response to swine flu, which met last week. It aims to deliver a report at the World Health Assembly meeting in May 2011.
Committee chairman Dr Harvey Fineberg said: 'What is evident just from the discussion we have had in these few days is that the committee will have to come to grips with this specific question of the place of severity in pandemic characterisation.'
The fact that debate around the issue had continued for many years was evidence of its complexity, he said.
'(This) suggests that it is a difficult problem, because if it were a simple problem, it would have been accommodated in an easy way long before,' Dr Fineberg said.
The question of severity in pandemics centred on three issues, he argued: how severity should be defined, how it should be measured and how it could account for differences in severity in different settings at the same time.
'All of these initial questions need to be very well appreciated and thought through in order to begin to answer this question - how could you combine severity and extent?' he said.
Challenges were also posed by making any assessment of severity meaningful and usable for the public, he pointed out.