People still should get their flu shot, and there's plenty available, Dr. Julie Gerberding, head of the Centers for Disease Control and Prevention, told The Associated Press.
So far, the majority of flu cases are being caused by strains that are a good match to the vaccine - and it should provide some cross-protection against the new bug, too, Gerberding stressed.
"We're still very optimistic" about the protection, Gerberding said. "If people haven't gotten their flu shot, it really is still not too late."
Every year, the flu infects up to 20 percent of the population, causes the hospitalization of 200,000 people and kills 36,000.
Flu is a virus, but it can make its victims vulnerable to bacterial infections, in the lungs or the bloodstream, at the same time.
Children are at particular risk, and the CDC this week sent an alert to doctors to watch for young flu victims who might also have such bacterial infections as the notorious drug-resistant staph known as MRSA.
Last year, the CDC learned of 73 children who died from flu, and 44 percent of them had a bacterial co-infection - mostly staph. Compared to earlier years, that's a five-fold increase in staph piggybacking on kids' flu.
While the CDC's newest flu report lists one child death so far this year, Gerberding wanted to be sure that doctors test for staph in any child with a suspicious illness "because these bacteria need special treatment, and we want to make sure they get that right therapy."
Each year's vaccine contains protection against three influenza strains - two members of the nasty Type A family, an H1N1 and an H3N2 version, plus a milder Type B - that experts predict will cause the most illness.
So far this year, H1N1 is causing the vast majority of disease, Gerberding said.
But a new H3N2 strain emerged near the end of Australia's flu season, too late to be included in the U.S. vaccine. Called H3N2/Brisbane-like, it is now sickening Americans, although it still is making for a small proportion of cases, Gerberding cautioned.
Some 132 million doses of vaccine were produced this year, more than ever before. It's too early to know how many people got vaccinated, but Gerberding said a record number of doses were distributed to doctors and other vaccine providers - and that there is still some available.
CDC has found flu affecting most of the country but widespread outbreaks in Alaska, Colorado, Hawaii, Kansas, Massachusetts, Mississippi, New Mexico, New York, Pennsylvania, Texas and Virginia.