Swine flu outbreak in 2009 much deadlier than prior estimate

The 2009 swine flu outbreak killed 15 times more people - an estimated 284,500 people - than were confirmed by laboratory tests at the time, according to a new study.

The study estimates that the death toll may have even reached as high as 579,000 people. An international group of scientists conducted the research, which was published in the Lancet journal on Tuesday. The original estimated number of deaths was pegged at 18,500 by the World Health Organization, Reuters reports.

"This pandemic really did take an enormous toll," Fatimah Dawood, the leader of the study, said, according to Reuters. "Our results also suggest how best to deploy resources. If a vaccine were to become available, we need to make sure it reached the areas where the death toll is likely to be highest."

The WHO warned that its initial estimate was a gross underestimate because of the deaths of people outside of the health system. The study showed that 51 percent of swine flu deaths occurred in southeast Asia and Africa.

The swine flu, caused by the H1N1 influenza virus, infected a victim in central Mexico in March 2009 and spread to California in April 2009. The virus then spread quickly worldwide.

The virus contained pieces of swine, bird and human flu viruses.

The WHO declared the flu a pandemic in June 2009 after cases were identified in 74 countries.