Bird flu may be less deadly than supposed, based on blood serum evidence of many past mild infections in Asia and elsewhere, a biomedical team reported Thursday.
Bird flu commonly travels from poultry to people, typically striking farmworkers, but not from person-to-person. Based on a review of about 600 cases, the World Health Organization estimated that the virus strain kills more than half its victims. That death rate looks overstated, according to a study released by the journal Science.
"WHO does not account for a majority of infections, but rather the select few hospitalized cases that are more likely to be severe," says the study led by microbiologist Taia Wang of the Mount Sinai School of Medicine in New York. That could mean an undercount of patients who suffer only minor bird flu illness, inflating the death rate.
The team compiled evidence of antibodies to the virus collected from 12,677 Asians, Africans and Europeans in 27 studies dating from 1997 to 2009. The team estimates that about 1.2% of them had survived mild bird flu cases. That corresponds to "millions of people who have been infected worldwide," the study says.
"The bottom line is that it looks like a whole lot of people become infected and don't die," says Columbia University virologist Vincent Racaniello, who was not part of the study. "How much lower the death rate is, we don't know."
For perspective, the 1918 flu that killed more than 675,000 people nationwide, often young and otherwise healthy, had a 0.5% death rate. A less-lethal bird flu similar to that outbreak would still be terrible. Seasonal flu has a death rate of about 0.1%, often felling the elderly.
University of Minnesota bioterrorism expert Michael Osterholm disagreed with suggestions of a lower death rate. The study included 1997 Hong Kong flu cases, ones before a deadly bird flu outbreak in 2004 that sparked worldwide concern. "That's just not a valid comparison," Osterholm says.
Osterholm belongs to the federal National Science Advisory Board for Biosecurity, which last year called for deleting details of two studies, scheduled for the journals Science and Nature, describing experiments aimed at making bird flu infectious among mammals. The experiments raised the prospect that if the mutated bird flu viruses escaped or could be reproduced, they could trigger a worldwide pandemic, which WHO experts estimated could kill more than 20 million people worldwide. A WHO summit that ended this week called for full publication of the two studies and for a halt to such research until stronger safety measures were assured in labs.
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