Nobody knows how many people would die if a new influenza pandemic strikes. So far, the World Health Organization (WHO) has been deliberately cautious in putting a number on the scope of such a disaster. But last week, the agency bowed to experts--including one from its own ranks--who have been ratcheting up the projected death toll in recent months, and said 50 million or more could die--at least seven times more than WHO's previous estimate.
The deadliness of a pandemic depends on many factors: the pathogenicity of the new virus strain, for instance, and the speed at which it spreads. Although the specter of millions of deaths might help inject a sense of urgency into the worldwide preparation campaign, says WHO flu chief Klaus Stöhr, such estimates may also erode trust if they prove too high. "We don't want to scare people," Stöhr says.
That's why WHO stuck to a conservative message. On its Web site, it cited data from the U.S. Centers for Disease Control and Prevention (CDC) in Atlanta, Georgia, showing that "today, a pandemic is likely to result in 2 to 7.4 million deaths globally." The numbers came from a computer model based on a virus strain like the one that caused a mild pandemic in 1968.
But others say the next pandemic strain could be more like the one that caused the 1918-19 Spanish flu, which claimed at least 20 million lives and perhaps many more. WHO's earlier numbers are "rather ridiculous," says Michael Osterholm, director of the University of Minnesota Center for Infectious Disease Research and Policy in Minneapolis. On 29 November, a similar message was sounded by Shigeru Omi, director of WHO's Western Pacific Region Office in Manila, who broke ranks by saying publicly that the toll could be as high as 20 million, 50 million, or "in the worst case," 100 million.
Initially, WHO had hoped to end the debate by coming up with new numbers itself. But there's simply too little anyone can say with any certainty, says WHO spokesperson Richard Thompson. So a carefully worded statement issued on 8 December simply concluded that experts' estimates "have ranged from 2 million to over 50 million." The statement called the earlier 2-to-7-million estimates "best-case scenarios."
The new statement is "still lacking in leadership," Osterholm says. But Peter Sandman, a risk communications consultant from Princeton, New Jersey, who has advised WHO, says the new statement is "a huge improvement" because it acknowledges the scientific uncertainty rather than favoring one scenario.