The 1990-91 winter flu season has been one of the mildest in decades, the Centers for Disease Control says.

No outbreaks have been reported in weeks, and the number of deaths - though not immediately available Monday - appears low, the federal agency said."It's been an incredibly slow flu year," Dr. Joe Kent, an epidemiologist with the CDC's flu branch, said in a recent interview. "It's one of the lightest we've had in 20 years."

CDC researchers don't keep score of every flu case in the United States because most cases are never reported.

But the agency does monitor trends in flu activity on a state-by-state basis. This winter 48 states reported confirmed or suspected flu cases, but only one state has reported an outbreak since January.

The dominant flu strain was Type B, one of the mildest, Kent said.

Another factor may have been this year's flu vaccine, which was a good match for the viruses floating around, researchers said. In some past years, new strains that people weren't vaccinated against popped up in mid-winter.

But even though 1990-91 was an off year, as many as 1 million Americans probably came down with the flu, Kent said. Even more may have been sent to bed with aches, pains and chills caused by other ailments.

"The fact that it's a slow flu season doesn't mean a lot less people had colds," he said.