THURSDAY, Feb. 23 (HealthDay News) -- The avian flu, which killed almost 60 percent of those known to be infected, actually struck many more people worldwide but didn't make them very sick, a new analysis finds.
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The actual fatality rate of the H5N1 flu strain, therefore, is probably less than 60 percent considering that millions of people may have been infected over the past eight years, the researchers report.
The analysis results confirm earlier findings, said one expert, Dr. Marc Siegel, an associate professor of medicine at New York University. It's still not clear how fatal the strain actually is, but the research "emphasizes that H5N1 is not as deadly in humans as is being proposed by some people," said Siegel, author of Bird Flu: Everything You Need to Know About the Next Pandemic.
Siegel added that he doesn't think "this particular virus is going to mutate to go easily from human to human. That's extremely unlikely."
Scientists and public health officials have been sounding the alarm for years about the potential that the avian flu strain called H5N1 could become a major threat to humans. As of last December, the World Health Organization (WHO) reported a total of 573 cases since 2003; of those, 59 percent died.
Fears about the strain are so intense that a controversy erupted this year over whether scientists might help bioterrorists by publishing details about their research into bird flu. The WHO agreed last week to allow the research, which examines a mutated and more contagious form of bird flu, to be published.
In the new report, researchers from Mount Sinai School of Medicine in New York City launched a combined analysis of 20 studies that examined blood test results from than 12,500 people. They found that 1 percent to 2 percent of them had signs that they'd been infected with the H5N1 infection. Most of those said they hadn't recently had cold or fever symptoms.
The research suggests that few people are being infected by the strain, Siegel said. It would be unusual for this particular type of flu to mutate in a dangerous way that could cause it to become contagious between people, he said.
Philip Alcabes, a professor of public health at City University of New York's School of Public Health at Hunter College, cautioned that the findings do show that the strain infects people more easily than previously thought.
"Does this mean H5N1 is more or less of a threat to human health? Really, the report changes nothing in that regard -- because the public health concern about avian flu is about the possibility of future change in the virus-human relationship. With this study we know a little more about the present virus-human relationship -- but we still don't have a crystal ball," Alcabes said.
"So it remains important to understand how animal viruses, including H5N1 and others, circulate among animals and how they migrate to human populations," added Alcabes, who was not involved in the new study.
The analysis appears in the Feb. 23 online issue of Science.
Copyright © 2012 HealthDay. All rights reserved.
SOURCES: Marc Siegel, M.D., associate professor, medicine, New York University,New York City; Philip Alcabes, Ph.D., professor, public health, City University of New York's School of Public Health, Hunter College, New York City; Feb. 23, 2012, Science, online