The virulent H5N1 strain of bird flu kills fewer people than current World Health Organization estimates that 60 percent of infections result in death, according to a new study.

The H5N1 bird flu strain has many fearing a reprisal of the 1918 Spanish flu outbreak that killed upwards of 50 million people worldwide.

However, the virulent strain may be more common than originally estimated, researchers concluded.

Virologists found H5N1 infections caused around 1-2 percent of flu cases across Asia, Europe and Africa, according to blood samples analyzed from 12,000 people.

The majority of the infected people did not become ill and none died, according to the study.

The World Health Organization criteria that are currently being used for confirmation of H5N1 infections are good for the identification of very severe cases, but they do not pick up the cases that are mild or asymptomatic, Taia Wang, lead researcher and postdoctoral student at the Mount Sinai School of Medicine, told the Los Angeles Times.

The results suggested that more people may be infected with bird flu than the 586 H5N1-linked deaths the WHO formally recognizes. Higher infection rates would translate to a fatality rate significantly lower than 60 percent, according to the study.

The journal Science published the study online Thursday.

The fatality rate of the seasonal flu is unclear, but the Centers for Disease Control and Prevention estimate that anywhere between 3,000 and 49,000 people died each year from the seasonal flu between 1976 and 2007, a fatality rate between 0.001 and 0.02 percent.

Humans become infected with H5N1 through contact, and health experts worry that bird flu will mutate and become transmittable by human-to-human contact.

That worry got a boost after researchers created bird flu strains that pass easily between ferrets, which react to the flu much like humans do. The U.S. government sought to block the publication of the super-virulent strains over fears that terrorists could use that research to create biological weapons.

Scientists argued that publication of the research is essential to prepare for a potential pandemic and develop vaccines. Researchers agreed last week to hold off on publishing and any further research until all issues are sorted out.

If direct transmission becomes possible, bird flu has the ability to wreak havoc even if the fatality rate is less than 60 percent.

You could reduce the seriousness of this virus twentyfold and it would still exceed that of the 1918 Spanish flu, Michael T. Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota, told the Los Angeles Times.

The 1918 Spanish flu pandemic killed 50 million people over the course of a year and a half and had a 3 percent fatality rate.

Osterholm disagreed with the results of the study. He criticized it for including people who were affected by the 1997 bird flu outbreak in Hong Kong, which was actually H1N1, not H5N1.

The virus was a bit different, he said in a press release.

If you remove those people from the numbers, only 0.5 percent of people would test positive for the illness, he said.