Wednesday, January 25, 2006

Early warning or false hope?

WHO is again encouraging Asian countries, where most of the human cases of bird flu have occurred, to tighten up their ability to detect and report cases quickly.
"The window of opportunity for containment is very narrow, meaning rapid containment measures must be carried out at least two to three weeks after detection of a potential pandemic event," Omi said in a speech to the WHO's Executive Board.

"However up to now, only half of the reports for human H5N1 cases meet this target. Some reports have been received as late as one or two months after disease onset," he added.


The WHO says that if a pandemic strain of the virus emerges, it may be possible to halt human-to-human spread, but only if "fire blanket" measures including distribution of antivirals and restrictions on movement of people are taken quickly. (Reuters)
There is no doubt prompt reporting might be important as a way to gain preparation time, but it is hard to credit WHO's public stance that doing so might allow smothering and outbreak at its inception with a "fireblanket" of antivirals if the virus gains the facility to move easily from human to human. About a year ago two research groups (in the Ferguson in the UK and Longini in the US) reported computer model results suggesting that under extremely optimistic assumptions this might be possible. Not only are the requirements indicated by the model stringent and unlikely, but the models themselves have many built-in assumptions that have never been validated. Thus the predictions of either of the models may be wide of the mark in any direction.

Recently we had two examples of ways this won't work. Turkey is held up as a case where we now have prompt reporting of human cases. But in the last two weeks we had cases of a traveler and a journalist who had returned from Turkey to their home countries but became ill either in transit or on arrival. At this point it is said neither had become sick from H5N1. But authorities in both countries (Belgium and France) understood clearly either or both could have been bird flu cases, and if the disease were passing easily from person to person this scenario would be even more likely.

My guess is that WHO knows this and is holding out the hope that a pandemic could be stopped in this fashion as an inducement to member nations to improve their surveillance and reporting capabilities. I truly hope that is their motivation, because if they really think they have the remotest chance of stopping H5N1 once it has adapted to humans, they are badly mistaken and are likely to make bad policy decisions.

Good surveillance and reporting can sound the alarm weeks earlier, giving precious time for the rest of the world to get ready to mitigate the consequences. But it won't stop an inflluenza pandemic from happening.