The swine flu virus, H1N1, may have killed 15 times the number of people counted by the World Health Organization, according to a new study. And unlike the seasonal flu, the H1N1 pandemic struck down mostly young people, many living in Africa and Southeast Asia.
Beginning in 2009, the virus swept the globe, and the WHO counted 18,500 swine flu deaths that had been confirmed by laboratory tests. But according to new estimates from researchers at the U.S. Centers for Disease Control and Prevention, the virus probably killed between 105,700 and 400,000 people around the world in its first year alone, and an additional 46,000 to 179,000 people likely died of cardiovascular complications from the virus.
That's a pretty wide gap in death rates, but it's not unusual. The numbers of flu deaths confirmed by lab tests usually understate how many people actually died from the virus, simply because most doctors around the world don't have the time or the resources to test their patients for the virus and report cases to health authorities.
"This is a problem year in and year out, from London to Nairobi," said Dr. William Schaffner, chair of preventive medicine at Vanderbilt University Medical Center. "It's so difficult to test everyone with influenza."
The problem is greater in countries with few medical resources.
"In some countries, data on influenza are quite sparse or nonexistent," said Dr. Fatimah Dawood, the study's lead author. And she said even if a patient is tested, sometimes the virus might not even be detectable.
The study, published today in the medical journal The Lancet, is the first attempt to provide a global estimate of how many deaths actually occurred during the first year of the swine flu pandemic.
Researchers were more surprised by who the virus targeted. According to the CDC analysis, 80 percent of deaths from the swine flu pandemic were of people under age 65, not the older, frail adults who are typically the victims of seasonal flu. Geographically, 59 percent of the deaths were in Africa and Southeast Asia.
"The number of potential years of life that were lost was far higher than what we would anticipate during a seasonal flu epidemic," Dawood said.
Though the virus was deadly, the swine flu pandemic is still considered to have been a fairly mild one. The CDC calculates that up to 575,000 people may have died from H1N1 in 2009. The WHO estimates that the seasonal flu kills up to 500,000 people each year. Both pale in comparison to the flu pandemic of 1918, which killed an estimated 50 million people worldwide.
"It just drives home how serious the disease can be -- that even the mildest pandemic we have an historic record of may have killed more than half a million people," said John Barry, author of "The Great Influenza."
Taking the flu seriously also involves taking annual vaccinations seriously. The CDC recommends that everyone over age 6 months get a flu shot each year.
"This should remind us in the fall that this is the time to get vaccinated," Schaffner said. "It's the best preventive measure we have available."