Lone Simonsen of George Washington University, author of the study published Monday, said the pandemic's impact was greatest in South and Central America, Livescience.com reported. Death rates were highest among younger people, he said.
Researchers realized a new strain of the H1N1 virus was spreading in April 2009. Within weeks, the strain had been found around the world.
A similar virus in 1918 was responsible for one of the worst epidemics in history, killing about 2 percent of the global population.
In 2010, as the pandemic was declared over, the World Health Organization said it had killed at least 18,500. But WHO said that was clearly an undercount, based only on cases confirmed in the lab.
Simonsen and other researchers used virology data from WHO and reports of deaths from respiratory disease in 21 countries, extrapolating from there to the rest of the world. They found that 62 percent to 85 percent of those who died in the pandemic were under 65, while seasonal flu tends to strike harder among the elderly.
The findings were published in PLoS Medicine.