By Erinn Connor
The number of deaths from the 2009 H1N1 flu pandemic may be up to 10 times higher than the World Health Organization's official count, according to a new study in PLOS Medicine.
Based on data from 26 countries, research led by George Washington University School of Public Health estimates that the flu virus was responsible for up to 203,000 deaths, compared to the 18,449 deaths reported by WHO.
The WHO numbers only consist of laboratory-confirmed deaths from H1N1, but the study authors noted the actual number is much higher because most people infected with the virus never got an H1N1 test. More notable is that researchers found that an estimated 62 to 85 percent of those who died were younger than 65 years old. Typically, most flu-related deaths are among the elderly, as they often have other chronic conditions that make them more susceptible to complications.
"This study confirms that the H1N1 virus killed many more people globally than originally believed," said lead author Lone Simonsen, PhD, a research professor in the department of global health at the George Washington University School of Public Health and Health Services. "We also found that the mortality burden of this pandemic fell most heavily on younger people and those living in certain parts of the Americas."
Researchers examined weekly virology data from WHO and mortality data from 21 countries that account for about 35 percent of the world's population. They used this to approximate the number of respiratory deaths (which often happens when H1N1 gets into the lungs and causes pneumonia) in each country, and used a formula to project the results across the globe.
Despite the high numbers, this outbreak pales in comparison to the 1918 flu pandemic, which killed approximately 50 million people, or 1 to 2 percent of the world's population. Still, the 2009 and 1918 flu have something in common: They both affected younger, healthier people more than the elderly or those with weakened immune systems, who are typically hit the hardest by the flu.
While the exact reason H1N1 affected mainly younger people is unknown, one possible explanation could be the lack of antibodies for H1N1.
The H1N1 strain was first found in the United States in April 2009 (it originated in Mexico), and had never been previously identified in humans or animals, according to the U.S. Centers for Disease Control and Prevention. The genes of the virus were related to the swine-lineage H1N1, thus giving it the name "swine flu." But because it was a previously undetected strain in humans, people have few antibodies to it like other flu strains and those in the seasonal flu vaccine provided no protection.
"Previous immunity can help protect people during seasonal flu outbreaks," said Catherine Troisi, PhD, an infectious disease epidemiologist at the University of Texas School of Public Health. "But the antibodies in the seasonal flu vaccine wouldn't protect anyone from H1N1."
Getting the flu death numbers right plays an important role in getting the public to take a potential pandemic seriously. The U.S. government declared a public health emergency in late April, and a global pandemic was declared by WHO in early June. Collecting data on flu outbreaks and reporting it to public health officials ensures that there is enough supply of vaccines, medications, and other protection equipment around the globe.
"Unless you've had the flu, people don't get that it's not just a bad cold," Troisi said. "If you're telling people, 'Yes, a lot of people were infected and we had this many deaths,' it helps people keep their guard up in the future. The problem is if public health is doing their job and the outbreak isn't a huge disaster, then people say they were overreacting."
The study noted the death numbers reported by WHO were only laboratory-confirmed cases. Most people with the flu aren't tested for specific strains of the flu. Troisi said a quick test at your primary care doctor's office is just to confirm if you have a flu virus, not what kind it is, as the antiviral treatment is the same no matter the strain.
In the case of H1N1 in America, the CDC developed a test for that strain quickly, but it was only recorded if a sample was sent to a CDC lab. Eventually state health departments were able to confirm the strain as well, but still not every flu case was recorded.
Despite the number discrepancy, the H1N1 pandemic helped prepare public officials on responding to future flu outbreaks on local, national and global levels. But it likely won't help in preventing the next pandemic.
"The response was quick unlike the response to SARS," Troisi said. "The vaccine came out in the fall just a few months after the initial outbreak. But as far as prevention goes, we know it's going to be coming from animals, and we could be doing a better job of monitoring what's likely to come."
"2009 H1N1 Flu Killed 10 Times More People Than Official Estimates" originally appeared on Everyday Health.