The 1918 pandemic was estimated at about 2 to 2.5, he said.
"In a sense, it's kind of reassuring in that it is highly transmissible but not exceptionally transmissible," Blumberg said. "On the other hand, we need to keep in mind that, unless you're someone who has already been infected with the swine flu, everybody in the world is susceptible to it. That's the scary part."
Given this vulnerability, Blumberg said, it makes sense that hospitals and communities are taking some extra precautions, such as using N-95 respirator masks.
Authorities have tried various strategies to mitigate the current outbreak, including closing schools, although federal officials in the United States are leaving that decision to local jurisdictions.
Recommended precautions for preventing the spread of swine flu include avoiding contact with other people if you are sick, coughing into your sleeve rather than your hand, and copious hand washing.
But the study authors said larger-scale measures may still be needed.
The study is the first completed by the new Preparedness Modeling Unit at the U.S. Centers for Disease Control and Prevention.
The U.S. Centers for Disease Control and Prevention has more on the H1N1 swine flu.
SOURCES: Nathaniel Hupert, M.D., MPH, co-director of Cornell University and Weill Cornell Medical College's joint Institute for Disease and Disaster Preparedness, New York City; Dean Blumberg, M.D., associate professor, pediatric infectious diseases, University of California, Davis Children's Hospital; Peter Gross, M.D., chief medical officer, Hackensack University Medical Center, New Jersey; Influenza and Other Respiratory Viruses; Associated Press
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