Health officials estimate that as many as one million Americans now have the new swine flu, or H1N1 influenza virus.

Lyn Finelli, a flu surveillance official with the Centers for Disease Control and Prevention, voiced the estimate at a vaccine advisory meeting Thursday in Atlanta.

The estimate is based on mathematical modeling. Nearly 28,000 U.S. cases have been reported to the CDC, accounting for roughly half the world's cases. The U.S. count includes 3,065 hospitalizations and 127 deaths.

An estimated 15 million to 60 million Americans catch seasonal flu each year.